United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-81-011
March 1981
Air
Philadelphia Oxidant
Data Enhancement Study
Analysis and Interpretation
of Measured Data
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EPA-450/4-81-011
Philadelphia Oxidant Data
Enhancement Study
Analysis and Interpretation
of Measured Data
by
Douglas AT lard, Michael Chan, & Chris Marlia
AeroVironment, Incorporated
145 Vista Avenue
Pasadena, California 91107
and
Dr. Edgar Stephens
Statewide Air Pollution Research Center
University of California at Riverside
Riverside, California 92521
Contract No. 68-02-3332
EPA Project Officer: Norman Possiel
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
March 1981
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This report was furnished to the U.S. Environmental
Protection Agency by AeroVironment Inc., Pasadena,
California, in fulfillment of Contract No. 68-02-3332.
The contents of this report are reproduced herein as
received from AeroVironment Inc. The opinions,
findings, and conclusions expressed are those of the
authors and not necessarily those of the
U.S. Environmental Protection Agency. Mention of
company or product names is not to be considered as an
endorsement by the U.S. Environmental Protection
Agency.
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SUMMARY
The objectives of this study were twofold:
1. To obtain air quality and meteorological data of sufficient extent and quality
to apply the Systems Application, Incorporated (SAI) photochemical model to
the Philadelphia area.
2. To recommend days suitable for model validation through analysis of field
data.
Sixteen surface air quality sites, eighteen surface meteorological sites, and three
upper-air meteorological sites contributed data to the study during the summer of 1979.
In addition, helicopter-based measurements of air quality and meteorology and measure-
ments of hydrocarbon species were performed.
Based upon analysis of all data, the following days were recommended for model
validation:
July 12 August 4 August 10
July 13 August 5 August 22
July 16 August 6
July 19 August 7
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ACKNOWLEDGEMENTS
Many people at AeroVironment Inc., besides the authors, contributed significantly to
this study. Other primary participants and their areas of responsibility are:
Mr. Robert Baxter, Field Manager
Mr. Don Gonzales, Data Processing
Ms. Diane Barker, Report Editing
Mrs. Darlene Asamura, Technical Typing
Ms. Gloria Best, Technical Illustrating
Mr. Timothy Press, Data Analysis
Mr. Howard Hammeren, Field Calibration
Mr. David Pankrantz, Senior Field Technician
Mr. Steven Fisher, Field Technician
Mr. David Emery, Field Technician
Mr. Stan Krzywonos, Field Technician
A number of other organizations were also involved in this study. The U.S. EPA's
Environmental Monitoring Systems Laboratory, Las Vegas, Nevada (EMSL-LV), supplied an
instrumented helicopter. Mr. Charles Fitzsimmons was responsible for EMSL-LV field
operations. The helicopter measurements were made by Northrop Services' Environmental
Science Center under the supervision of Mr. Calvin Hancock. Mr. Barry Martin, EPA
Environmental Monitoring and Support Laboratory, Research Triangle Park, North
Carolina, and his staff gave invaluable assistance with instrumentation problems. Finally,
the contribution of Mr. Norm Possiel, EPA Project Officer, to the technical direction of
the project is certainly one of the most appreciated.
u
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TABLE OF CONTENTS
SUMMARY i
ACKNOWLEDGEMENTS li
LIST OF FIGURES iii
LIST OF TABLES ix
1. INTRODUCTION 1
2. FIELD MEASUREMENT PROGRAM 2
2.1 Objectives of the Field Program 2
2.2 Program Design 2
2.3 Surface Measurements at Fixed Sites 3
2.3.1 Special Study Sites 3
2.3,2 Existing Air Quality/Meteorology Monitoring Stations 8
2.3.3 Supplemental Meteorological Sites 14
2.3.14 Special PAN/Nitric Acid/NOx Monitoring 14
2.4 Aircraft Measurements of Air Quality and Meteorology 14
2.5 Balloon Measurements of Upper Air Meteorology 19
2.3,1 Radiosonde Releases 19
2.5.2 Pibal Releases 19
2.6 Hydrocarbon Species Measurements 22
2.7 Quality Assurance 22
2.7,1 Surface Monitoring Program 24
2.7,2 Audits 26
2.8 Data Reduction and Compilation Procedures 27
3. OZONE AND PRECURSOR CONCENTRATIONS IN THE STUDY AREA 29
3.1 Data Summaries 29
3.1.1 Representativeness of the 1979 Summer Months 29
3.1.2 Average and Maximum Levels of Pollutants 32
3.1,3 Ozone Wind Roses 36
3.2 Hydrocarbon Species Analysis 42
3.2.1 Data Summary 42
3.2.2 Acetylene/n-Butane Ratios 46
3.2.3 Hydrocarbon Data Validity 47
3.2.4 Limitation of Analytical Scheme 48
4. CASE STUDY DAYS 53
4.1 July 12, 1979 (Thursday) 61
4.1.1 Synoptic Meteorology 61
4.1.2 Mesoscale Meteorology 61
4.1.3 Precursor Patterns 65
4.1.4 Ozone Patterns 65
4.1.5 NO2 Patterns 69
4.1.6 Concentrations Aloft 69
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TABLE OF CONTENTS
4.2 July 13, 1979 (Friday) 72
4.2.1 Synoptic Meteorology 72
4.2.2 Mesoscale Meteorology 72
4.2.3 Precursor Patterns 75
4.2.4 Ozone Patterns 75
4.2.5 NO2 Patterns 80
4.2.6 Concentrations Aloft 80
4.3 July 16, 1979 (Monday) 83
4.3.1 Synoptic Meteorology 83
4.3.2 Mesoscale Meteorology 83
4.3.3 Precursor Patterns 86
4.3.4 Ozone Patterns 86
4.3.5 NO Patterns 89
4.3.6 Concentrations Aloft 89
4.4 July 19, 1979 (Thursday) 92
4.4.1 Synoptic Meteorology 92
4.4.2 Mesoscale Meteorology 95
4.4.3 Precursor Patterns 95
4.4.4 Ozone Patterns 98
4.4.5 NO- Patterns 101
4.4.6 Concentrations Aloft 101
4.4.7 Hydrocarbon Species Data 101
4.5 August 4, 5, 6, 7, 1979 (Saturday, Sunday, Monday, Tuesday) 104
4.5.1 Synoptic Meteorology 104
4.5.2 Mesoscale Meteorology 110
4.5.3 Precursor Patterns 115
4.5.4 Ozone Patterns 121
4.5.5 NO- Patterns 133
4.5.6 Concentrations Aloft 133
4.5.7 Hydrocarbon Species Data 141
4.6 August 10, 1979 (Friday) 144
4.6.1 Synoptic Meteorology 144
4.6.2 Mesoscale Meteorology 144
4.6.3 Precursor Patterns 147
4.6.4 Ozone Patterns 147
4.6.5 NO- Patterns 151
4.6.6 Concentrations Aloft 151
4.6.7 Hydrocarbon Species 154
4.7 August 22, 1979 (Wednesday) 157
4.7.1 Synoptic Meteorology 157
4.7.2 Mesoscale Meteorology 160
4.7.3 Precursor Patterns 160
4.7.4 Ozone Patterns 160
4.7.5 NO- Patterns 163
4.7.6 Concentrations Aloft 163
IV
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TABLE OF CONTENTS
5. CONCLUSIONS 167
5.1 Morning Ozone Levels Aloft 167
5.2 Ozone Levels in the Philadelphia Urban Plume 169
5.3 Mesoscale Transport 171
5A Synoptic Transport 173
5.5 Days Recommended for Model Verification 173
6. BIBLIOGRAPHY 175
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LIST OF FIGURES
Number Description
1 Locations of monitoring sites set up specifically for the study 5
2 Exterior view of the monitoring station at Site 5 9
3 Existing air quality/meteorological monitoring stations 10
used in the study
4 Locations of supplemental meteorological monitoring sites 15
used in the study
5 EPA-LAS Vegas instrumented UH-1H helicopter 17
6 Locations of helicopter soundings and sampling sites 20
7 Locations of ground-level sampling sites 23
8 Ozone wind rose for Summit Bridge, DE 37
9 Ozone wind rose for Downingtown, PA 38
10 Ozone wind rose for Lumberton, NJ 39
11 Ozone wind rose for Robbinsville, N3 40
12 Ozone wind rose for Van Hiseville, N3 41
13 Total ion chromatograph from ambient air sample 51
14 Ozone profile over Summit Bridge, DE at 0535 EST on 58
August 10, 1979
15 Synoptic situation, 0700 EST, July 12, 1979 62
16 Synoptic trajectory of air parcels arriving at Philadelphia 63
at 1300 EST, July 12, 1979
17 Streamline analysis depicting surf ace flow across the study 64
area at 0700 EST on July 12, 1979
18 Isopleths of ozone at 1300, 1400, and 1500 EST, duly 12, 1979 67
19 Surface trajectory for various air parcels located within the 68
study area on duly 12, 1979
VI
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LIST OF FIGURES
20 Diurnal profiles of ozone at upwind sites on July 12, 1979 71
21 Synoptic situation, 0700 EST, July 13, 1979 73
22 Synoptic trajectory of air parcels arriving at Philadelphia 74
at 1300 EST, July 13, 1979
23 Isopleths of ozone at 0900, 1100, 1200, and 1300 EST, 77
July 13, 1979
24 Surface trajectory for various air parcels located within the 79
study area on July 13, 1979
25 Diurnal profiles of ozone at upwind sites and Chester, PA on 81
July 13, 1979
26 Synoptic situation, 0700 EST, July 16, 1979 84
27 Synoptic trajectory of air parcels arriving at Philadelphia 85
at 1300 EST, July 16, 1979
28 Isopleths of ozone at 1200, 1300, and 1400 EST, July 16, 1979 88
29 Surface trajectory for various air parcels located within the 90
study area on July 16, 1979
30 Diurnal profiles of ozone at upwind stations on July 13, 1979 91
31 Synoptic situation, 0700 EST, July 19, 1979 93
32 Synoptic trajectory of air parcels arriving at Philadelphia 94
at 1300 EST, July 19, 1979
33 Diurnal profiles of PAN at upwind sites and Van Hiseville, NJ 97
on July 19, 1979 and July average
34 Isopieths of ozone at 1400, 1500, and 1600 EST, July 19, 1979 99
35 Surface trajectory for various air parcels located within the 100
study area on July 19, 1979
36 Diurnal profiles of ozone and NO at upwind stations on 102
July 19, 1979
37a Synoptic situation, 0700 EST, August 4, 1979 106
37b Synoptic situation, 0700 EST, August 5, 1979 107
37c Synoptic situation, 0700 EST, August 6, 1979
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LIST OF FIGURES
37d Synoptic situation, 0700 EST, August 7, 1979 109
38a Synoptic trajectory of air parcels arriving at Philadelphia 111
at 1300 EST, August 4, 1979
38b Synoptic trajectory of air parcels arriving at Philadelphia 112
at 1300 EST, August 5, 1979
38c Synoptic trajectory of air parcels arriving at Philadelphia 113
at 1300 EST, August 6, 1979
38d Synoptic trajectory of air parcels arriving at Philadelphia 114
at 1300 EST, August 7, 1979
39 Isopleths of ozone at 1400, 1500, 1600, and 1700 EST, 122
August 4, 1979
40 Isopleths of ozone at 1400, 1500, 1600, and 1700 EST, 123
August 5, 1979
41 Isopleths of ozone at 1400, 1500, 1600, and 1700 EST, 124
August 6, 1979
42 Isopleths of ozone at 1400, 1500, 1600, and 1700 EST, 125
August 7, 1979
43 Streamline analysis depicting surface flow across the study 126
area at 1500 EST on August 4, 1979
44 Surface trajectory for various air parcels located within the 128
study area on August 4, 1979
45 Surface trajectory for various air parcels located within the 129
study area on August 5, 1979
46 Surface trajectory for various air parcels located within the 131
study area on August 6, 1979
47 Surface trajectory for various air parcels located within the 132
study area on August 7, 1979
48 Ozone concentrations reported during helicopter transects 136
during mid-afternoon flight on August 4, 1979
49 Vertical profiles of O-j, NOx, and Temperature obtained 137
by the instrumented helicopter over West Chester, PA at
0758 EST on August 5, 1979
vm
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LIST OF FIGURES
50 Ozone concentrations reported during helicopter transect 138
from downtown Philadelphia to iMedford, NJ on August 5, 1979
at an altitude of approximately 550 m MSL
51 Vertical profiles of O,, NO , and Temperature obtained 140
by the instrumented helicopter over Pottstown, PA at 0628 EST
on August 7, 1979
52 Synoptic situation, 0700 EST, August 10, 1979 145
53 Synoptic trajectory of air parcels arriving at Philadelphia 146
at 1300 EST, August 10, 1979
54 Isopleths of ozone at 1300, 1400, 1500, and 1600 EST, 149
August 10, 1979
55 Surface trajectory for various air parcels located within the 150
study area on August 10, 1979
56 Vertical profiles of O,, iNO , and Temperature obtained 152
by the instrumented helicopter over Summit Bridge, DE at
0535 EST on August 10, 1979
57 Ozone concentrations reported during helicopter transect from 153
Brandywine, PA to Philadelphia on August 10, 1979 at an
altitude of approximately 850 m MSL
58 Diurnal profiles of ozone at Summit Bridge, DE and Downingtown, 155
PA on August 10, 1979
59 Synoptic situation, 0700 EST, August 22, 1979 158
60 Synoptic trajectory of air parcels arriving at Philadelphia 159
at 1300 EST, August 22, 1979
61 Isopleths of ozone at 1400 and 1500 EST, August 22, 1979 162
62 Surface trajectory for various air parcels located within the 164
study area on August 22, 1979
63 Diurnal profiles of ozone at Downingtown, PA and Summit Bridge, 166
DE on August 22, 1979
IX
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LIST OF TABLES
Number Description
1 Responsible organizations and periods of operation of fieid 4
monitoring program components
2 Meteorological and air quality parameters monitored at the 6
five sites set up specifically for the study
3 Monitoring instruments with their lower detetection limits, 7
data precision, and lower limits of data validity
14 Meteorology and air quality parameters monitored at 11
existing stations
5 Site locations and operating agencies of the existing air 12
quality/meteorology stations
6 Locations of existing air quality/meteorology monitoring 13
sites with respect to Philadelphia urban core
7 Locations of supplemental meteorological monitoring sites 16
with respect to Philadelphia urban core
8 Parameters measured by helicopter and instruments used 18
9 Summary of aircraft sampling missions actually flown 21
10 Comparison of meteorological parameters recorded during each 30
summer month of 1979 with corresponding long-term means
11 Summary of high ozone days from 3uly 2 through September 31
18, 1979 for the study year and the previous four years
at Bristol, Pennsylvania
12 Summary of ozone data collected during the summer of 1978 33
and 1979 at the same location
13 Peak and average ozone precursor concentrations for the study 34
period at all air quality monitoring sites
14 Ozone frequency distribution for the study period at several 35
sites in and around Philadelphia
15 Species breakdown of Franklin Institute samples 44
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LIST OF TABLES
32 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the
ratio of NMHC to NO for rural and urban sites on August 10
/C
33 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the 161
ratio of NMHC to NO for rural and urban sites on August 22
\
34 Summary of morning ozone concentrations observed generally 168
upwind on case study days
35 Locations of peak ozone concentrations with respect to 170
Philadelphia
36 Source areas for peak ozone levels and areas impacted by 172
emissions from Philadelphia's central business district as
determined by mesoscale surface trajectories
xu
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LIST OF TABLES
16 Species breakdown of industrial site samples 45
17 Distribution of hydrocarbon species in simultaneous sample 49
pairs, taken at Lancaster and Downingtown, Pennsylvania,
respectively
18 Urban mixing heights for the case study days as determined 55
from radiosonde released from downtown Philadelphia
19 Time when rural mixing heights first exceeded 1000 m as 57
determined by AV Acoustic Sounder at Summit Bridge, Delaware
20 Peak O, and NO, concentrations, wind data, and helicopter 60
data availability Tior case study days for the entire study area
21 6:00 to 9:00 a.m. LOT averages of NO and NMHC and the 66
ratio of NMHC to NO for rural and urban sites on 3uly 12
22 6:00 to 9:00 a.m. LOT averages of NO and NMHC and the 76
ratio of NMHC to NO for rural and urban sites on July 13
23 6:00 to 9:00 a.m. LOT averages of NO and NMHC and the 87
ratio of NMHC to NO for rural and urban sites on July 16
.X
24 6:00 to 9:00 a.m. LOT averages of NO and NMHC and the 96
ratio of NMHC to NO for rural and urban sites on July 19
25 Maximum ozone and NO- concentrations observed in the study 105
area during the period August 4 through August 7, 1979
26 Vertical extent of thermal roots as determined from acoustic 116
sounder data at Summit Bridge, DE
27 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the 117
ratio of NMHC to NO for rural and urban sites on August 4
A
28 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the 118
ratio of NMHC to NO for rural and urban sites on August 5
X
29 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the 119
ratio of NMHC to NO for rural and urban sites on August 6
30 6:00 to 9:00 a.m. LDT averages of NO and NMHC and the 120
ratio of NMHC to NO for rural and urban sites on August 7
A
31 Average mixed layer ozone concentrations aloft on August 4, 134
4, 5, 6 and 7, 1979
XI
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1. INTRODUCTION
The Clean Air Act Amendments of 1977 require states to submit State Implementa-
tion Plans (SIPs) that demonstrate the attainment of the National Ambient Air Quality
Standard (NAAQS) for ozone (and certain other pollutants) by 1982. If such attainment is
shown to be impossible using reasonably available control measures, an extension to 1987
can be granted. To assist the states in developing their SIPs, the U.S. Environmental
Protection Agency (EPA) is conducting a program to provide technical information and
guidance on available procedures for estimating control requirements needed to attain the
NAAQS for ozone.
Photochemical models, particularly the Systems Applications, Incorporated (SAI),
Airshed Model (Reynolds et al., 1978) can be used to quantify control requirements. The
EPA plans to verify this model for several urban areas which typify different
photochemical and meteorological regimes. When this model is verified, the EPA will be
in a position to establish the range of the model's applicability and to issue guidance on its
application.
One of the urban areas under study is Philadelphia, Pennsylvania. Considerable
information on the transport of ozone and precursors into the Philadelphia area was
obtained in a study conducted in 1978 (Chan et al., 1979), even though the primary
emphasis of that study was to evaluate and demonstrate different approaches to measure
such transport. To enhance the data base for verifying the Airshed Model, another study
was conducted in Philadelphia in the summer of 1979. Besides gathering data for model
verification, another objective of that study was to increase our knowledge of the
photochemical and meteorological processes which lead to peak ozone and NO., concen-
trations in Philadelphia.
This report documents the data collection efforts of the 1979 study, characterizes
the air quality and meteorology during the monitoring period, investigates periods of high
ozone and NO-, with modeling potential, and provides recommendations for model
verification.
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2. FIELD MEASUREMENT PROGRAM
Data were collected from July 2, 1979 through September 18, 1979. These data
included continuous surface air quality measurements at fifteen locations, surface
meteorological measurements at seventeen locations, aircraft measurement of air quality
and meteorological parameters in the vertical, upper air meteorology at three locations,
and hydrocarbon species measurements.
2.1 OBJECTIVES OF THE FIELD PROGRAM
The primary objective of the field program was to obtain air quality and meteoro-
logical data of sufficient extent and quality to apply the Systems Application, Incor-
porated (SAI), photochemical model to the Philadelphia area. A secondary objective was
to collect data which would increase the EPA's knowledge of the photochemical and
meteorological processes which lead to peak ozone and NO- concentrations in a portion of
the Northeast Corridor. Philadelphia was selected because it is a large city within the
Northeast Corridor capable of generating high ozone levels while remaining subject to
significant inter-urban ozone/precursor transport.
2.2 PROGRAM DESIGN
To achieve the objectives of the field program, measurements were taken in the
vicinity of Philadelphia, Pennsylvania, to assess:
the levels of ozone and precursors transported into the study area;
the levels of precursors produced from emissions within the study area;
the highest levels of NO- and ozone downwind of the Philadelphia urban area.
The field monitoring program had four components:
1. Surface measurements of air quality and meteorology at fixed sites;
2. Aircraft measurements of air quality and meteorology;
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3. Balloon measurements of upper air meteorology;
'4. Hydrocarbon species measurements.
Table 1 shows the periods during which each of these field components contributed
data to the study and the organizations responsible for each component's operation.
2.3 SURFACE iMEASUREMENTS AT FIXED SITES
The fixed surface station component consisted of:
1. Five stations set up specifically for the study (special study sites);
2. Eleven existing air quality meteorological monitoring stations;
3. Supplemental meteorological sites;
4. Special PAN/nitric acid/NO monitoring.
J\
2.3.1 Special Study Sites
Figure 1 shows the locations of the five stations set up specifically for the study.
Table 2 lists the parameters monitored at each of these AeroVironment-operated sites.
Table 3 lists the instruments used, their precision, lower detection limit, and lower limit
of data validity. All monitoring equipment at these sites, with the exception of the
acoustic sounder used to measure mixing height at Site 1, was provided by the EPA's
Environmental Monitoring and Support Laboratory in Research Triangle Park, North
Carolina.
Sites 1 and 2 were upwind of Philadelphia under prevailing flow which was from the
south-southwest to west. Site 1 was near Summit Bridge, Delaware, approximately 60 km
southwest of the Philadelphia urban core. Site 2 was near Downingtown, Pennsylvania,
approximately 50 km west of Philadelphia. Site 2 was at the same position as one of the
sites in the 1978 Philadelphia Oxidant Study, thus providing some year-to-year data
comparison.
Sites 1 and 2 were to monitor ozone and precursors transported into the city, both
along the surface and aloft, when the prevailing flow was southwesterly. Surface stations
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Table 1. RESPONSIBLE ORGANIZATIONS AND PERIODS OF OPERATION OF FIELD MONITORING
PROGRAM COMPONENTS.
Program
Component
Dates
Responsible Organization
Surface Measurements of Air Quality and Meteorological Data at Fixed Sites
Special study sites
Existing sites
Supplemental
meteorological sites
Special PAN/nitric acid
NO monitoring
A
July 2-September 18
Duly 2-September 18
July 2-September 18
July 15-August 22
AeroVironment Inc. /U.S. Environmental Protection
Agency
Philadelphia Department of Health (Air Management
Services)
Pennsylvania Department of Environmental Resources
New Jersey Department of Environmental Protection
National Weather Service
Federal Aviation Administration
U.S. Air Force, U.S. Navy
Washington State University
Battelle Columbus Laboratories
Aircraft Measurements of Air Quality and Meteorological Data
Bell UH-1H helicopter
July 18-August 16
Northrop Services/U.S. Environmental Protection
Agency, Environmental Monitoring Systems
Laboratory, Las Vegas
Balloon Measurements of Upper Air Meteorological Data
Pibal
Radiosonde
3uly 16-August 16
July 18-August 26
U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Las Vegas
Beukers Laboratories, Inc.
Hydrocarbon Species Measurements
July 15-August 15
Washington State University
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,J _>—-"r— ' -«^I-.f _ _.lr I-I .f
PENNSYLVANIA
_ "IT " 7V^.,T">-V V^ N 5..LO-B*
FIGURE 1. Locations of monitoring sites set up specifically for the study.
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Table 2. METEOROLOGICAL AND AIR QUALITY PARAMETERS MONITORED AT THE FIVE
SITES SET UP SPECIFICALLY FOR THE STUDY.
Component
Ozone
Nitrogen Dioxide
Oxides of Nitrogen
Nitric Oxide
Non-Methane Hydrocarbon
Total Hydrocarbon
Methane
Carbon Monoxide
Wind Speed
Wind Direction
Temperature
Solar Radiation
Mixing Height
Site
1
Summit
Bridge, DE
X
X
X
X
X
X
X
X
X
X
X
X
2
Downing-
town, PA
X
X
X
X
X
X
X
X
X
3
Lumber-
ton, NJ
X
X
X
X
X
X
X
X
X
X
X
X
4
Robbins-
viile, NJ
X
X
X
X
X
X
X
5
Van Hise-
ville, N3
X
X
X
X
X
X
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Table 3. MONITORING INSTRUMENTS WITH THEIR LOWER DETECTION LIMITS, DATA
PRECISION, AND LOWER LIMITS OF DATA VALIDITY.
Parameter
Instrument
Instrument Lower
Detection
Limit
Data
Precision
Lower Limit
of Data
Validity
Air Quality
°3
NO
N02
N0x
THC
CH^
NMHC
CO
Bendix 8002
Bendix 8101
Bendix 8101
Bendix 8101
Beckman 6800
Beckman 6800
Beckman 6800
Bendix 8501
0.001 ppm
0.005 ppm
0.005 ppm
0.005 ppm
0.100 ppm
0.100 ppm
0.200 ppm
0.500 ppm
0.005 ppm
0.010 ppm
0.010 ppm
0.010 ppm
0.100 ppm
0.100 ppm
0.200 ppm
0.500 ppm
0.005 ppm
0.010 ppm
0.010 ppm
0.010 pprn
0.100 ppm
0.100 ppm
0 . 200 pprn
0.500 pprn
Meteorology
Wind Speed
Wind Direction
Temperature
Solar Radiation
Mixing Height
Climatronics
Climatronics
Climatronics
Eppley (Model 2)
AeroVironment 300C
0.2 m/s
N/A
N/A
0.05
cal/cm /min
30 m
0.2 m/s
5°
0.5° C
0.05
2
cal/cm /min
10 m
0.2 m/s
N/A
N/A
0.05
2
cal/cm /min
30 rn
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can provide an indication of transport aloft, since ozone and precursors trapped aloft
overnight are brought to the ground through turbulent vertical mixing after the breakup of
the nocturnal radiation inversion. Placing the acoustic sounder at Site 1 provided the
time of inversion breakup.
Sites 3, 4, and 5 were downwind of Philadelphia under prevailing flow. Site 3 was
near Lumberton, New Jersey, approximately 35 km east-northeast of the Philadelphia
urban core. Site ^ was near Robbinsville, New Jersey, approximately 60 km northeast of
Philadelphia. Site 5 was near Van Hiseville, New Jersey, approximately 75 km east-
northeast of Philadelphia. These sites were established to monitor peak ozone and NG>2
concentrations resulting from ozone and precursors transported into Philadelphia and
precursors emitted in the urban core under southwesterly flow. Figure 2 shows an
exterior view of the monitoring station at Site 5, which was identical to the monitoring
stations at Sites 1, 2, 3, and 4.
2.3.2 Existing Air Quality/Meteorology Monitoring Stations
Figure 3 shows the locations of the eleven existing air quality/meteorology monitor-
ing stations which contributed data to the study, and Table k lists the parameters
monitored at each. The state and local agencies operating these sites are named in
Table 5. The operating agencies themselves supplied most of the air quality and
meteorological instruments. The EPA's Environmental Monitoring and Support Laboratory
in Research Triangle Park, North Carolina, supplied some additional instrumentation.
Information on the accuracy, precision, and ranges of the instruments can be obtained
from the agencies themselves.
The EPA selected the stations to be included in the study based primarily upon
location and instrumentation available. Sites 6, 11, and 15 were included as upwind
stations for south to southwest flow and monitored transport of ozone and precursors into
the study area under these flows. Sites 9, 12, 13, and 14 were urban sites for monitoring
both urban generated precursors and urban ozone peaks or, in the case of Site 9, urban
wind flow. Site 10 provided a near-urban monitor. Sites 7, 8, and 16 served as downwind
ozone and/or NO2 stations under southwesterly flow. Table 6 gives the distances and
bearings from the urban core for these stations.
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FIGURE 2. Exterior view of the monitoring station at Site
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PENNSYLVANIA
FIGURE 3. Existing air quaiity/meteoroiogicai monitoring stations used in the study.
10
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Table 1. METEOROLOGY AND AIR QUALITY PARAMETERS MONITORED AT EXISTING STATIONS.
Component
Ozone
Nitrogen Dioxide
Oxides of Nitrogen
Nitric Oxide
Non-Methane
Hydrocarbon
Carbon Monoxide
Wind Speed
Wind Direction
Temperature
Site
6
X
X
X
X
X
X
7
X
X
X
X
X
X
8
X
X
X
9
X
X
10
X
X
X
X
11
X
X
12
X
X
X
X
X
13
X
X
X
X
X
X
14
X
X
X
X
X
15
X
X
X
X
16
X
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Table 5. SITE LOCATIONS AND OPERATING AGENCIES OF THE EXISTING
AIR QUALITY/METEOROLOGY STATIONS.
Site
Number
Location
Operating
Agency
Chester, Pennsylvania
Bristol, Pennsylvania
North Philadelphia Airport
Philadelphia, Pennsylvania
Allegheny
Philadelphia, Pennsylvania
10 Camden, New Jersey
11 Ancora, New Jersey
12 South Broad and Spruce Streets
Philadelphia, Pennsylvania
13 Franklin Institute
Philadelphia, Pennsylvania
Air Management Services Laboratory
Philadelphia, Pennsylvania
Claymont, Delaware
16 New Brunswick, New Jersey
Pennsylvania Department of
Environmental Resources
Pennsylvania Department of
Environmental Resources
Air Management Services
(Philadelphia Department
of Health)
Air Management Services
(Philadelphia Department
of Health)
New Jersey Department of
Environmental Protection
New Jersey Department of
Environmental Protection
Air Management Services
(Philadelphia Department
of Health)
Air Management Services
(Philadelphia Department
of Health)
Air Management Services
(Philadelphia Department
of Health)
Delaware Department of
Natural Resources and
Environmental Control
New Jersey Department of
Environmental Protection
12
-------
Table 6. LOCATIONS OF EXISTING AIR QUALITY/METEOROLOGY
MONITORING SITES WITH RESPECT TO PHILADELPHIA
URBAN CORE.
Site
Number
6
7
8
9
10
11
12
13
14
15
16
Location
Chester, Pennsylvania
Bristol, Pennsylvania
North Philadelphia Airport
Philadelphia, Pennsylvania
Allegheny, Pennsylvania
Camden, New Jersey
Ancora, New Jersey
South Broad and Spruce Streets,
Philadelphia, Pennsylvania
Franklin Institute,
Philadelphia, Pennsylvania
Air Management Services Lab,
Philadelphia, Pennsylvania
Claymont, Delaware
New Brunswick, New Jersey
Position with Respect to
Philadelphia Urban Core
Distance
(km)
20.3
30.5
16.0
6.2
f.8
38.9
CBD*
2.5
9.0
28.1
85.0
Bearing
Direction
WSW
NE
NNE
NE
E
SE
CBD*
NNW
N
WSW
NE
*CBD = central business district
13
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2.3.3 Supplemental Meteorological Sites
Data were also obtained from eight existing meteorological monitoring stations
operated by the National Weather Service, the Federal Aviation Administration, the U.S.
Air Force, and the U.S. Navy. Figure 4 shows the locations of these stations. All sites
recorded one-minute averages of wind speed, wind direction, and temperature once an
hour. These data were included to better define the study area wind field. Table 7 gives
the distance and bearing from the urban core for these stations.
2.3.4 Special PAN/Nitric Acid/NOx Monitoring
Special PAN, nitric acid, and oxides of nitrogen monitoring was conducted by
Washington State University and Batteile Columbus Laboratories during July 15 through
August 22, 1979, at Downingtown, PA (Site 2), and Van Hiseville, NJ (Site 5). Washington
State University monitored NO, NO and PAN at Downingtown, and Batteile monitored
X
nitric acid at Downingtown, and NO, NO , PAN, and nitric acid at Van Hiseville.
Information regarding measurement methods can be obtained directly from these
organizations.
2.4 AIRCRAFT MEASUREMENTS OF AIR QUALITY AND METEOROLOGY
The primary objective of the aircraft measurements was to obtain vertical profiles
and cross-sections of ozone and precursors to quantify pollutant transport aloft. That is,
from these profiles and cross-sections, we could find the levels of ozone and precursors
transported into the city in layers aloft over various periods during days of high
photochemical activity. Such measurements would also provide boundary and initial
conditions for verifying of the SAI model.
Aircraft measurements were taken by the EPA's Environmental Monitoring Systems
Laboratory in Las Vegas, and Northrop Services, Inc., between July 18 and August 16,
1979, using a Bell UH-1H helicopter (Figure 5). Parameters measured included O.,, NO,
NO^, visible light scattering, temperature, and dew point versus location and time. In
addition, hydrocarbon grab samples were taken for species analysis. The hydrocarbon
sampling will be discussed in more detail later in this chapter. Table 8 lists the
-------
U > i • w-mi '-w^r.'ITit*^, ,_'Lim- \ ;*
PENNSYLVANIA
FIGURE 4. Locations of supplemental meteorological monitoring sites used in the study.
15
-------
Table 7. LOCATIONS OF SUPPLEMENTAL METEOROLOGICAL MONITORING
SITES WITH RESPECT TO PHILADELPHIA URBAN CORE.
Site
Number
8
17
13
19
20
21
22
23
Location
North Philadelphia Airport, PA
Philadelphia International Airport, PA
McGuire Air Force Base, NJ
Willow Grove Naval Air Station, PA
Lakehurst Naval Air Station, NJ
Trenton-Mercer County Airport, NJ
Millville Airport, NJ
Greater Wilmington Airport, DE
Position with Respect to
Philadelphia Urban Core
Distance
(km)
16.0
9.1
49.2
28.6
75.8
48.2
64.3
47.6
Bearing
Direction
NNE
SW
E
N
E
NE
S
SW
16
-------
FIGURE 5. EPA-Las Vegas instrumented UH-1H helicopter.
17
-------
Table 8. PARAMETERS MEASURED BY HELICOPTER AND INSTRUMENTS
USED.
Parameter
Instrument
Hydrocarbons
Ozone
NO/NO 2/NO
Light Scattering
Temperature/Dew Point
Static Pressure (altitude)
Position
Grab samples using evacuated stainless steel
canisters
REM 612 B chemiluminescent analyzer
Monitor Labs 8440 chemiiuminescent analyzer
Meteorology Research Inc. Model 1550
nephelometer
EG&G 137-C1
National Semiconductor LX3702A
Two Collins DME W
18
-------
instruments used. The accuracy, precision, and ranges of these instruments have been
previously documented (Hancock, 1980).
The aircraft (helicopter) measurement program consisted of 10 days of intensive
vertical soundings and transects upwind, over, and downwind of the study city. The choice
of these 10 days was based on forecasts predicting meteorological conditions favorable for
significant photochemical activity.
On each measurement day, three flights were generally made: one in the early
morning (takeoff at 0500 EST), one at mid-morning (takeoff at 0900 EST), and one in the
early afternoon (takeoff at 1300 EST).
Each flight consisted of vertical soundings over three surface monitoring stations
from as close to the ground surface as possible up to 2 km above ground level (AGL), and a
horizontal traverse between the stations at the elevation where maximum ozone levels
were observed. Figure 6 shows the locations of these stations. Spirals were performed at
two upwind and one downwind sites during the early morning; one upwind, one downtown,
and one downwind site during the late morning; and one downtown and two downwind sites
during the afternoon. The specific sites over which sampling was performed varied
depending upon the wind direction. The exact flight paths taken on each sampling day
have been documented elsewhere (Hancock, 1980).
The mission of each day was to obtain information about ozone and precursor
concentrations aloft being transported into the study area, concentrations present aloft
near the central business district, and peak ozone concentrations downwind. Table 9
summarizes the aircraft sampling missions actually flown.
2.5 BALLOON MEASUREMENTS OF UPPER AIR METEOROLOGY
2.5.1 Radiosonde Releases
Beukers Laboratories, Inc. was responsible for releasing five radiosondes per day
from July 18 through August 26, 1979, from 315 East Chelten Avenue, Philadelphia (about
10 miles west-southwest of North Philadelphia Airport). These five releases provided
19
-------
FIGURE 6. Locations of helicopter sounding and sampling sites.
20
-------
Table 9. SUMMARY OF AIRCRAFT SAMPLING MISSIONS ACTUALLY
FLOWN.
Date
duly 23
duly 25
August 4
August 5
August 6
August 7
August 10
August 14
August 15
August 16
Flight Time
(EST)
1044-1243
1*32-1658
0532-0737
0854-1052
1314-1530
0919-1124
1308-1536
0738-0938
1305-1530
0517-0741
0907-1057
1316-1525
0517-0723
0844-1050
1301-1507
0519-0724
0832-1045
1258-1527
0522-0723
0851-1043
1300-1530
0519-0732
0848-1126
1317-1515
0510-0715
0835-0927
Pattern*
Southwesterly
Southwesterly
Westerly
Westerly
Westerly
Westerly
Westerly
Westerly
Westerly
Northwesterly
Northwesterly
Northwesterly
Northwesterly
Northwesterly
Northwesterly
Southwesterly
Northwesterly
Northwesterly
Southwesterly
Southwesterly
Southwesterly
Northwesterly
Northwesterly
Northwesterly
Northwesterly
Northwesterly
*The exact sounding locations for each flight pattern varied.
21
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vertical profiles of wind speed, wind direction, temperature, and dew point for the hours
0500, 0700, 0900, 1200, and 1500 EST. The 0700 and 1200 EST releases provided data at
"mandatory" levels (surface, 1000 mb, 850 mb, 700 mb, and 500 mb), while the 0500, 0900,
and 1500 EST releases provided data at other significant levels (based upon temperature
lapse rate).
2.5.2 Pibal Releases
The EPA Environmental Monitoring Systems Laboratory in Las Vegas, Nevada
(EMSL-Las Vegas), was responsible for releasing and tracking approximately 12 pilot
balloons per weekday from July 16 through August 16, 1979, from Robbinsville Airport,
iNew Jersey (Site 4), and from Greater Wilmington Airport, Delaware (Site 23). These
releases provided vertical profiles of wind speed and direction for 0500 EST through
1600 EST.
2.6 HYDROCARBON SPECIES MEASUREMENTS
This component of the program, which was the responsibility of Washington State
University, provided information on the hydrocarbon species as they were transported into
and emitted within the urban area.
There were three parts to the sampling program: (1) integrated samples were
collected at ground level; (2) grab samples were collected at ground level; and (3) grab
samples were collected aloft. Samples were collected between July 15 and August 15,
1979.
Figure 7 shows the ground level sampling locations. One-hour integrated samples
were taken at the Franklin Institute (Site 13) and at a site near an industrial area in south
Philadelphia along the Delaware River. Eighty-five of these samples were collected from
0600 to 0700 EST and 0800 to 0900 EST. On selected days, a surface grab sample was
collected at each of two roving sites, the location of which varied from day to day.
Fourteen of this type of samples were collected. Four grab samples were collected by the
EPA-EMSL helicopter during each flight day for a total of forty. Nine samples were
collected for intercomparison purposes. A grand total of 148 samples were analyzed.
22
-------
FI = Franklin Institute
15 = Industrial Site
Rl-6 = Roving Sites
FIGURE 7. Locations of ground-levei sampling sites.
23
-------
All samples were analyzed within 24 hours of collection. The gas chromatography
procedures used to analyze these samples are documented elsewhere (Westberg and
Sweany, 1980).
2.7 QUALITY ASSURANCE
This section summarizes the procedures used to assure data quality for AeroViron-
ment's portion of the field program, and specifically describes the calibration methods and
frequency, station check methods and frequency, and audit and interlaboratory tests.
2.7.1 Surface Monitoring Program
The equipment listed in Table 3, except for the acoustic radar, was tested and
furnished to AeroVironment by the EPA. Both EPA and AV extensively bench-tested all
equipment to assure proper operation. To meet the manufacturers' specifications, the
equipment and recording devices were installed in environmentally controlled shelters at
each of the five stations. Additional air conditioners were installed at all sites to insure
that stations were operating within the specified temperature range.
o Calibration of Air Quality Instruments
AV personnel performed multipoint calibrations of all air quality instruments at
each station at least monthly throughout the measurement program. In addition, an
instrument was calibrated whenever any of the following conditions occurred: (a) the
control limit for the span check as specified in the Station Check List Log was exceeded;
(b) after repair of a malfunctioning analyzer; (c) after replacement of major components
of an analyzer; and (d) when the audit results exceeded the limits established (see
discussion of audits, Section 2.7.2). Zero plus a minimum of four calibration points
equally spaced over the analyzer range were used to generate a calibration curve. A
"master" calibrator was used for all of the multipoint calibrations to ensure data
comparability. The purpose of the multipoint calibrations was twofold: (a) to check the
instrument linearity; and (b) to assign the values of the on-site calibration sources used
for daily station checks so that they would be traceable.
-------
Dynamic calibration of the NO-NC^-NO and (X analyzers was performed using a
Monitor Labs calibrator. For NO and NO channels, a National Bureau of Standards
Standard Reference Material (NBS SRM) gas cylinder containing approximately 50 ppm
NO in N2 was diluted to ambient levels for the calibration. For the NO? channel, AV used
gas phase titration (GPT) of NO and O3 prescribed by the EPA (40 CFR, Part 50,
Appendix F).
For the O^ analyzers, the calibrator's O, output was determined on site by the
ultraviolet (UV) photometry method (M Federal Register 8221-8233, February 8, 1978). A
modified Dasibi Model 1003-AH ozone monitor served as a transfer standard. Gas
cylinders containing approximately 100 ppm NO in N9 were used for the NO/NO spans.
L. A.
To calibrate the THC/ChL instruments, two compressed gas cylinders containing
zero ppm and approximately 8 ppm of CI-L in an ultrapure air were used. Two compressed
gas cylinders containing zero ppm and approximately 50 ppm of CO in an ultrapure air
with about 350 ppm CO., were used to calibrate the CO analyzer. In both cases,
multipoint calibrations were performed using an AeroVironment Model BB-100 dilution
system. All gas cylinders were NBS-traceable.
The NO flow rate and dilution system of the calibrator and the flow rate for the
AeroVironment Model BB-100 dilution system were calibrated with a bubble flowmeter at
the beginning, mid-way through, and at the end of the measurement program.
o Calibration of Meteorological Equipment
Calibration checks of the meteorological equipment were done on site. The wind
cups were turned to make sure that the bearings were in normal condition. The wind
vanes were aligned to the true north, true south, and true north again to calibrate the
recorder output. The local magnetic north declination of +10° was accounted for. The
temperature output from each station was checked using an NBS-traceable mercury
thermometer.
25
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o Station Checks
AV personnel checked stations daily using the Station Check List Log prepared for
the project. Their primary concerns were to ensure that the analyzers and the supporting
equipment were in proper working order.
Zero and span were checked for ail gaseous analyzers during the station check. For
the NO/NO and O, instruments, this was done by using the on-site Monitor Labs
Model 8500 calibrator. For the hydrocarbon analyzer, a zero cylinder containing
hydrocarbon-free air and a span cylinder containing approximately 2 ppm of CH^ in
uitrapure air were used. A similar procedure for CO was used, with the span cylinder
containing approximately 50 ppm CO in uitrapure air.
The zero and span values for each instrument were used to determine control limits.
The control limits were a useful tool to detect early instrument problems.
Hydrocarbon analyzers were precision-checked three times a week using
EPA-furnished gas cylinders containing known concentrations of hydrocarbon. The results
of these checks were recorded and forwarded to the EPA.
The station check personnel reported any instrument problems to the Field Manager
on the same day so that corrective action could be initiated as soon as possible. In
addition, the Field Manager provided a weekly instrument status report to AV's Program
Manager in Pasadena, California, to update him on the field program status and to enable
him to provide direction when needed.
2.7.2 Audits
Quality assurance verification of the O^, NO-NO2-NOx, THC-CH^, and CO systems
used for calibrating was done at Research Triangle Park, North Carolina, at the start of
the measurement program. The agreements for all systems were within 5%.
During the monitoring phase, the project was further audited by Research Triangle
Institute (RTI) under contract to the EPA. Each of the five surface monitoring stations
were audited twice. RTI also audited other study participants.
26
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The acceptable criteria for ail audits were set at + \5% agreement for the slope of
regression analysis of the audit data. Any audit results indicating that these limits were
exceeded resulted in prompt recalibration or repair/recalibration of the instrument(s) in
question.
2.3 DATA REDUCTION AND COMPILATION PROCEDURES
The continuous air quality and meteorological data AV collected on chart recorders
were reduced at AV's main office in Pasadena, CA. The data were digitized, tabulated,
and spot-checked for obvious instrument malfunctions and unusual data points. Site logs,
field personnel, and project scientists were consulted concerning the validity of unusual
data points. Calibration factors were applied to the data, as appropriate, using the
monthly multi-point calibration data supplemented by the daily zero and span check
values.
The air quality and meteorological data collected by federal, state, and local
agencies were provided to AV by EPA in tabulated form. These data were merged with
data collected by AV to form a data set with consistent units and time reference (Eastern
Standard Time -- EST). AV prepared data volumes containing hourly averages of all these
data for all the sites.
AV also obtained hard copy printouts of supplemental meteorological data collected
by the National Weather Service, Federal Aviation Administration, U.S. Navy, and U.S.
Air Force. AV entered these data into the computer, error checked them, and produced a
magnetic tape.
Special PAN/nitric acid/NO data collected by Washington University and Battelle
Columbus Labs were provided to AV by EPA in hard copy and magnetic tape format.
These data were entered in a form consistent with the rest of the data base, error
checked, and a magnetic tape produced.
In addition, EPA provided AV with data recorded by the EPA EMSL-Las Vegas
aircraft. These data were sent in hard copy and magnetic tape format along with hard
copies of pollutant profiles measured during soundings. These data were used during the
analysis.
27
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Hard copy printouts of pibal data from Trenton, New Jersey, and Wilmington,
Delaware, collected by EPA EMSL-Las Vegas were provided by EPA for use in the
analysis. Upper air radiosonde data collected by Beukers Labs were provided to AV by
EPA on magnetic tape for use in the analysis.
Finally, hydrocarbon species data collected by Washington State University were
provided to AV by EPA in hard copy format for use in the analysis.
28
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3. OZONE AND PRECURSOR CONCENTRATIONS IN THE STUDY AREA
3.1 DATA SUMMARIES
This section summarizes the data collected during the 1979 field program. It also
briefly compares data collected during the study with data collected during recent years
and, when possible, with long-term means to determine how representative the study
period was with respect to characteristic ozone concentrations.
3.1.1 Representativeness of the 1979 Summer Months
Table 10 compares some meteorological parameters recorded in each of the summer
months of 1979 with the corresponding long-term means at the Philadelphia International
Airport. The average maximum monthly temperatures were lower than the long-term
mean during July, August, and September of 1979, whereas the average minimum monthly
temperature was higher than the long-term mean during each of those months. Moreover,
the mean monthly temperature (which is the average of the minimum and maximum
temperatures) indicates that July was slightly cooler and August and September slightly
warmer than the long-term mean. Another useful statistic for relating long-term
meteorological data to ozone climatology is the number of days in each month with
temperatures greater than or equal to 90° F- From Table 10, we can see that even though
the mean temperature for July 1979 was lower than the long-term mean, July 1979 had a
normal number of days during which the temperature reached or exceeded 90 F.
August 1979 had two days more and September 1979 had two days less than the
corresponding long-term means. Also, July had less precipitation and August and
September had more precipitation than normal, and each of the three months had less
sunshine than normal.
Table 11 summarizes the number of high ozone days and the number of episode
periods (three or more consecutive high ozone days) from July 2 through September 18 for
the study year and the previous four years at Bristol, Pennsylvania. At this site, peak
ozone concentrations were generally lower in the study year than in the four previous
29
-------
Table 10. COMPARISON OF METEOROLOGICAL PARAMETERS RECORDED DURING EACH SUMMER MONTH
OF 1979 WITH CORRESPONDING LONG-TERM MEANS.
Meteorological
Parameter
Average Maximum
Monthly Temperature
Average Minimum
Monthly Temperature
Mean Monthly
Temperature ( C)
Number of Days with
Maximum Temperature
(>_ 90° F)
Total Precipitation (cm)
Average Station
Pressure (mb)
Average Wind Speed
(rn/sec)
Percent of Possible
Sunshine
Number of
Years in
Long-Term
Average
30
30
30
17
30
4
36
34
July
1979
29.3
19.7
24.6
7
10.0
1,015.9
3.3
46
Long-Term
30.4
19.3
24.9
7
10.4
1,014.4
3.6
63
August
1979
28.8
19.5
24.2
7
15.1
1,015.9
3.6
52
Long-Term
29.3
18.2
23.8
5
10.4
1,016.9
3.5
63
September
1979
24.8
15.7
20.3
0
12.4
1,017.3
3.9
52
Long-Term
25.8
14.3
20.1
2
7.7
1,017.1
3.7
60
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Table 11. SUMMARY OF HIGH OZONE DAYS (greater than 0.100 ppm and 0.120 ppm) FROM
JULY 2 THROUGH SEPTEMBER IS, 1979, FOR THE STUDY YEAR AND THE PREVIOUS
FOUR YEARS AT BRISTOL, PENNSYLVANIA (the national ambient air quality
standard for ozone is 0.120 ppm).
Year
1979
1978
1977
1976
1975
Number of Days
with Peak O
(ppm)
>0.100
14
21
23
1*
24
>0.120
4
13
11
6
10
Number
of
Episode*
Cases
0(0)
3(5)
3(4)
0(0)
1(4)
Total
Number of
Observations
(maximum
possible 79)
71
63
68
45
67
Percent of Days
with O3
(ppm)
>0.100
19.7
33.3
33.8
31.1
35.8
>0.120
5.6
20.6
16.2
13.3
14.9
*An episode is defined as three or more consecutive days with O^ measurements greater than
0.100 ppm. Numbers in parentheses indicate the number of days in the longest episode.
-------
years. For the study period, less than 20% of the daily maximum concentrations were
greater than 0.100 ppm, whereas during each of the previous four years more than 30% of
the days exceeded this value. A similar reduction in the number of days exceeding
0.120 ppm was noted.
While one might infer from the above discussion that maximum ozone levels were
lower in 1979, conditions at Bristol, Pennsylvania may not be indicative of the entire
study area. A field program similar to the one for this study was performed in the
summer of 1978 to evaluate measurement approaches for studying ozone and precursor
transport into an urban area (Chan et al., 1979). Four of the sites contributing data to
that study were also used in this study. Table 12 summarizes data collected at these sites
during the two summers. From this table, we can see that ozone levels were generally not
substantially different between the two years.
3.1.2 Average and Maximum Levels of Pollutants
Table 13 gives peak and average daily maximum ozone concentrations as well as
peak and average morning (0500 through 0800 EST) precursor concentrations observed at
all monitoring locations during the study period. Site locations were shown in Figures 3
and 14. Ozone levels were similarly high even at some stations located predominantly
upwind. Precursor concentrations were generally quite low except at downtown locations.
Table 14 is a frequency distribution of ozone levels observed at various sites in and
around Philadelphia. The greatest frequency of concentrations in excess of 0.12 ppm
occurred at outlying stations. Downingtown, PA (Site 2), to the west of Philadelphia, and
Lumberton, NO (Site 3), to the east, each had relatively high frequencies of observations
(>.85%) greater than 0.12 ppm compared to downtown Philadelphia (<.15%). This pattern
is also true for frequency of ozone values greater than 0.08 ppm. Sites 1 through 5 had
concentrations greater than 0.08 ppm for more than 3.5% of the observations, whereas in
downtown Philadelphia (Site 12) the frequency is less than 1.0%. The high frequency of
low ozone concentrations at Site 12 was expected due to the higher levels of
ozone-scavenging NO in urban areas. Surprisingly, the frequency of high ozone levels at
outlying sites is somewhat independent of the direction from Philadelphia. Sites to the
west or southwest have roughly the same frequency of concentration levels in excess of
32
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Table 12. SUMMARY OF OZONE DATA COLLECTED DURING THE SUMMER OF 1978 AND 1979 AT THE SAME
LOCATION.
Location
Downingtown,
Pennsylvania
Ancora ,
New Jersey
South Broad and
Spruce Streets
(Philadelphia)
Franklin Institute
(Philadelphia)
Site
Number
2
11
12
; 13
Peak
1978
0.1*2
0.142
0.180
0.250
1979
0.146
0.147
0.140
0.150
Number of Days
with Peak O, (ppm)
>0.100
1978
11
15
7
6
1979
11
15
4
4
>0.120
1978
3
4
2
5
1979
6
6
1
1
Daytime Monthly Averages
Jul
1978
—
0.049
0.028
0.036
Jul
1979
0.057
0.051
0.030
0.031
Aug
1978
0.055
0.052
0.024
0.030
Aug
1979
0.044
0.047
0.020
0.029
Sep
1978
0.041
0.034
0.018
0.024
Sep
1979
0.042
0.039
0.013
0.020
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TABLE 13. PEAK AND AVERAGE OZONE PRECURSOR CONCENTRATIONS (in ppm) FOR THE STUDY
PERIOD AT ALL AIR QUALITY MONITORING SITES.
Site
No.
1
2
3
b
5
6
7
8
10
11
12
13
11
15
16
Location
Summit Bridge, DE
Downingtown, PA
Lurnbei ton, N3
Robbinsville, N3
Van Iliseville, N3
Chester, PA
Bristol, PA
North Philadelphia
Airport, PA
Camden, N3
Ancora, NJ
South broad & Spruce Sts.
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
Air Management Services
Lab, Philadelphia, PA
Claymont, DE
New Brunswick, N3
Ozone
Maximum
Hourly
Average
0.137
0.157
O.I'|6
0.111
0.161
0.183
0.135
0.160
0.161
0.117
0.1*0
0.150
0.160
0.170
0.105
Mean Daily
Maximum
3ul
0.080
0.087
0.079
--
0.078
0.077
0.073
0.077
0.078
0.079
0.057
0.061
0.071
0.070
—
Aug
0.072
0.068
0.078
0.072
0.072
0.071
0.080
0.079
0.076
0.078
0.011
0.058
0.059
0.062
0.056
Sep
0.058
0.061
0.052
0.052
0.051
0.061
0.060
0.053
0.055
0.060
0.026
O.O'll
0.056
0.033
0.038
Oxides oj Nitrogen
Maximum
Hourly
Average
0.063
0.083
0.13I
0.207
0.082
-
-
-
-
—
-
—
—
-
—
Morning Average
(0500-0800 EST)
Jul
0.010
0.019
0.025
-
0.012
-
-
0.012
0.068
—
0.069
0.068
0.055
-
—
Aug
0.006
0.013
0.022
0.028
0.007
-
--
0.031
0.052
-
0.059
0.060
0.057
-
--
Sep
0.012
0.022
0.021
0.018
0.010
-
-
0.037
0.080
—
0.035
0.067
0.059
~
—
Non-Methane Hydrocarbons
Maximum
Hourly
Average
1-0
1.1
1.5
--
-
6.6
1.7
—
—
—
2.9
1.7
3.1
-
—
Morning Average
(0500-0800 EST)
3ul
0.1
O.I
0.1
-
-
1.1
0.5
—
—
—
0.6
0.8
0.6
-
—
Aug
0.2
O.I
0.1
-
-
1.0
—
-
—
—
0.3
0.3
0.1
-
-
Sep
1 0.3
0. 1
0.1
-
-
1.3
—
—
—
—
0.3
0.3
0.5
-
—
-------
Table 14. OZONE FREQUENCY DISTRIBUTION FOR THE STUDY PERIOD AT SEVERAL SITES IN AND
AROUND PHILADELPHIA.
Site Name
Summit, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, NJ
Van Hiseville, N3
South Broad Street, PA
Total Hours Observed with Specified Ozone Concentration (ppm)
Site
1
2
3
4
5
12
.000-.039
990
994
1,194
807
1,111
1,430
.040-.079
541
689
480
202
487
224
.080-.099
97
81
70
38
69
11
.100-.120
15
27
30
9
19
9
>.120
8
17
16
4
8
2
Total
1,651
1,808
1,790
1,060
1,694
1,676
-------
0.08 ppm as do sites to the east and northeast. This suggests the importance of ozone
transport within the Northeast Corridor.
3.1.3 Ozone Wind Roses
Ozone wind roses for Sites 1 through 5, shown in Figures 8 through 12, give some
information concerning the general source areas of these high concentrations. These
depict simultaneously the frequency distribution of ozone concentrations and wind
direction. The wind directions associated with high ozone concentrations are easily
identified from these figures. Some data are not included in Figures 8 through 10 since
coincident wind direction and ozone data were not available. It is not expected that these
data would significantly alter the wind direction frequency distribution.
Site 1 is southwest of the Philadelphia urban area. However, at this site ozone
concentrations greater than 0.12 ppm generally occurred with winds from the west or
west of southwest and concentrations greater than 0.10 ppm generally occurred with
winds from the northwest, west or southwest. This indicates that high ozone levels at this
site are associated with surface transport from source regions (such as Baltimore or
Washington D.C.) other than Philadelphia.
Site 2 is west of the Philadelphia area. During the field study, ozone concentrations
greater than 0.12 ppm at this site generally occurred with winds from the east, southeast
or south which suggests that the Philadelphia urban plume affects this site. This differs
from the case during the summer of 1978 when winds from the southeast were only
associated with ozone concentrations lower than 0.08 ppm (Chan et al., 1979). However,
winds from the southeast were much less frequent during the summer of 1978 than during
the summer of 1979 and, as can be seen from Figure 9, the ozone concentrations with the
greatest frequency associated with southeast winds in 1979 were less than 0.08 ppm.
Site 3 is east of the Philadelphia urban area. From Figure 10 we can see that ozone
concentrations higher than 0.12 ppm at this site occur with winds ranging from the west
to south to east. Only winds from the north or northwest are not associated with high
ozone levels at this site.
36
-------
(~n .030 - .099 ppm
.100 - .120 ppm
>.i2o
t
N
0% 5% 10%
Relative Frequency of Occurrence
FIGURE 8. Ozone wind rose for Summit Bridge, DE (Site 1).
37
-------
^.000 - .039 ppm
B .040 - .079 ppm
n~l .0X0 - .099 ppm
I—1 .100 - .120 ppm
>.120 ppm
I i
t
N
0% 5%
Relative Frequency of Occurrence
10%
FIGURE 9. Ozone wind rose for Downingtown, PA (Site 2).
3S
-------
HI.OOO - .039 ppm
1=^.040 - .079 ppm
FT! .080 - .099 ppm
I—| .100 - .120 ppm
mm >.i2o
Relative Frequency of Occurrence
! l I I I I
t
N
o%
10%
FIGURE 10. Ozone wind rose for Lumberton, NJ (Site 3).
39
-------
- .039 ppm
f=) .040 - .079 ppm
FT! .OSO - .099 ppm
I—I .100 - .120 ppm
irnro >.i2o
0%
Relative Frequency of Occurrence
5%
t
N
10%
FIGURE 11: Ozone wind rose for Robbinsville, NJ (Site
-------
0%
BB-000 - .039 ppm
gE3.0.120 ppm
Relative Frequency of Occurrence
5%
t
N
10%
FIGURE 12. Ozone wind rose for Van Hiseville, NJ (Site 5).
-------
Sites 4 and 5, northeast of Philadelphia, record high ozone levels with winds from
the southwest indicating the effects of the Philadelphia urban plume. Moreover, as with
Site 3, Site 5 also measures high ozone levels with winds from the southeast. This finding
is unexpected since flow from this direction is usually associated with high pressure off
the coast to the northeast. Sites 4 and 5 also show some ozone levels higher than
0.10 ppm with winds from the northwest, indicating some long-range transport.
3.2 HYDROCARBON SPECIES ANALYSIS
The 148 samples analyzed between mid-July and mid-August by Washington State
University (WSU) fall into several different categories.
1. Over half (85) of the samples were taken in the morning either at the Franklin
Institute site (Site 13) near center city or at the "industrial site" in south
Philadelphia (see Figure 7 for sampling locations). Of these, half were taken
at each site between 0500 and 0600 EST and the other half between 0700 and
0800 EST. This forms the most uniform data set in the study and includes data
from six of the ten case study days to be discussed in Chapter 4.
2. Five afternoon samples were taken at the industrial site between 1300 and
1400 EST.
3. A set of 35 samples was taken by EPA/Las Vegas at various locations. Fifteen
of these were taken on five of the case study days.
4. A group of fourteen roving samples was taken at various points in the
Philadelphia area.
5. Another set of nine samples was taken for intercomparison purposes at various
locations.
3.2.1 Data Summary
Most of the samples were taken between duly 17 and August 15, 1979, during a
consistent sampling program at the Franklin Institute (Site 13) and at a site in south
-------
Philadelphia near the industrial area along the Delaware River. Franklin Institute is
within a few blocks of the City Hall which is in the center of Philadelphia. Integrated
samples were taken from 0500 to 0600 EST and from 0700 to 0800 EST at each site for
about 20 days during the heart of the study. The distribution by types (%) along with the
total identified (known) species and the sum, including unidentified peaks for this block of
data, are given in Tables 15 and 16. The averages for each of the two sites and two
collection times are also given. The most striking feature of these averages is that there
is so little difference between the four sets of data. Paraffins make up about two-thirds
of the total, aromatics about one fourth, oiefins (omitting ethylene) about 6% and
acetylene 2%. This distribution is valid at both sites at both hours even though individual
samples depart from this average significantly.
It is also noteworthy that the average total NMHC at the Franklin Institute site
(Site 13) for the 0700 to 0800 EST samples was slightly higher than for any of the other
three sets of data. This provides no support for the idea that industrial emissions are the
major source of hydrocarbon pollution in the Philadelphia area. If industrial emissions
were the major source of hydrocarbons, the industrial site would be expected to show the
higher hydrocarbon concentrations. The higher value at 0700 to 0900 EST at Franklin
Institute may reasonably be ascribed to the higher traffic levels at this location at the
later hours.
Some departures from the average type distribution can be explained by reviewing
the species distribution. Before citing examples of this, it is well to note that these
anomalies normally affect only individual samples, not samples taken at different sites on
the same day or at different times at the same day. The early Franklin Institute sample
of 3uly 20, 1979, showed high paraffins and low aromatics, while the sample taken later at
Franklin Institute and the early sample at the industrial site showed just the reverse.
Review of the species data reveals very high concentrations of butane and pentanes,
suggesting that this sample contained hydrocarbons from a nearby gasoline vapor source.
This sample also contained large concentrations of light oiefins, especially propene, which
are more difficult to explain. On July 24, 1979, all four samples contained the highest
levels of NMHC in the entire set. The industrial site samples were nearly average in type
composition while the Franklin Institute samples were both high in paraffins and low in
aromatics. Again, referral to the species distribution reveals high levels of light
-------
Table 15. SPECIES BREAKDOWN OF FRANKLIN INSTITUTE SAMPLES.
Date
July 17
July 18
July 19**
July 20
July 23*
July 2
-------
Table 16. SPECIES BREAKDOWN OF INDUSTRIAL SITE SAMPLES.
Date
July 17
July 18
July 19*-
July 20
July 23*
July 21
July 25*
July 26
July 27
July 30
July 31
August 1
August 2
August 3
August f««
August 5'»
August 6'-
August 7«»
August S
August 9
August 10*-
August If*
Augusi 15*
Average/
Standard
Deviation
0500 to 0600 E.ST
(percent)
Acetylene
3
2
2
2
3
0
1
0
—
2
2
2
2
2
2
2
3
2
2
0
1
3
Oleljn
5
6
5
1
9
9
7
8
—
2
:
S
2
5
6
3
7
i*
5
5
3
IS
5
1.9/1 6/3.1
Aromatic
13
25
32
31
27
20
25
36
_
35
35
IS
31
25
19
27
21
27
10
31
19
12
20
26/9
Paraffin
79
68
60
61
61
71
66
55
_
60
60
72
65
69
73
68
71
66
81
61
18
69
73
66/8
(ppeC)
Known
1031
131
376
160
392
1119
350
S60
—
2SS
288
285
189
157
2S2
255
167
273
817
336
663
310
189
Sum
1511
520
118
575
575
1700
193
1130
—
361
361
315
226
539
307
290
550
272
878
118
711
367
5E-S
603/387
n-Butane Ratio
0.277
0.156
0.367
0.28!
C.268
0.012
0.060
C.100
—
0.326
0.326
0.079
. 116
.226
. Ill
.207
.356
.113
.038
.228
.075
.358
0.236
0700 to OSOO £5T
July 17
July 18
July 19**
July 20
July 23*
July 21
July 25*
July 26
July 27
July 30
August 1
August 2
August 3
August 1**
Augusi 5*
August 6*»
Augusi 7*»
August 8
August 9
August 10*-
August 11*
Augusi 15*
Average/
Standard
Deviation
3
1
3
—
1
1
0
I
3
3
1
3
2
2
5
1
2
3
1
2.5/1
„
9
5
—
7
S
(4
10
I*
5
0
5
5
15
2
S
5
9
7
u
6.6/2.9
21
21
37
—
20
21
15
31
50
32
11
28
26
16
30
23
27
15
21
25
21
21.9/S.5
69
63
56
—
73
69
81
58
13
59
75
65
66
67
63
65
66
67
66
66
78
72
65.S/8
561
106
511
—
786
831
S21
108
<*76
330
818
217
568
136
230
588
330
181
387
257
375
302
809
558
630
—
1018
101"
9S8
572
666
385
975
278
700
532
255
691
399
507
152
306
119
316
592/251
0.210
0.523
0.179
—
0.073
0.131
0.030
0.138
0.132
0.389
0.067
0.010
0.195
0.131
0.112
0.383
0.127
0.155
C.278
0.102
0.377
* Helicopter data avauaole
»Case study oay
-------
paraffins. So gasoline vapor is suggested, although the propane is also quite high in both
Frankiin Institute samples. The industrial site samples on July 24, 1979, were unusually
high in olefins, even higher carbon number oiefins. The two 2-hexenes totaled 39 ppbC in
the early sample. This source signature is not recognizable. One-hexene was high also on
August 10, 1979, at the industrial site in the later sample, but benzene was unusually high
in the early sample that day (185 ppbC).
The type distribution, indeed the individual species distributions, are strongly
suggestive of gasoline composition. It would be very useful to know the species
composition of the gasoline sold in the Philadelphia area. Even more valuable would be
information on the brand-to-brand variations in fuel composition. Lacking this specific
information, comparison can be made only with the rather meager open literature on
gasoline composition. One of the most complete analyses was reported by the Shell Oil
Company, Wood River Laboratory (Sanders, 1968; Maynard, 1969). Two fuels were
analyzed with no claim to representativeness. They each contained about 60% paraffin,
30% aromatics, and the balance olefin. This is consistent with the type distribution in the
Philadelphia study. The detailed breakdown by species also shows similarities with the
fuel analysis.
It is evident from this data set that, while the species distributions are similar in
different areas and at different times, some samples show excesses of small groups of
hydrocarbons. With more information on signatures it might be possible to identify the
sources of these hydrocarbons.
3.2.2 Acetylene/n-Butane Ratios
Acetylene is of interest in studies of this kind, not because it is toxic or
photoreactive, but because it is almost exclusively derived from automobile exhaust. It is
not present in gasoline (or any other motor fuel) but is formed in the engine. Since it is
one of the least reactive of atmospheric hydrocarbons, it serves as a good tracer for
engine exhaust.
Normal butane (n-butane) is also of fairly low reactivity but it enters the
atmosphere from several sources: automobile exhaust, gasoline vapor, vaporized gasoline,
-------
as well as industrial sources. The ratio of these two hydrocarbons then should give a
measure of the contribution of automobile exhaust to any given sample. If each ambient
sample represents exhaust emissions from a large number of vehicles, and if the n-butane
is all due to exhaust, this ratio should be approximately constant and equal to that found
in average automobile exhaust. Mayrsohn et al. (1977) used a ratio of about 2 acetylene
to 1 n-butane for their source reconciliation studies. Since air samples showed lower
values, substantial contributions of n-butane from other sources were indicated. In fact,
Mayrsohn et al. attributed roughly one-half the total hydrocarbon to automobile exhaust
based on their source reconciliation procedure.
The acetylene/n-butane ratios from the present study are tabulated in Tables 15 and
16. Most values are much lower than the 2:1 ratio used by Mayrsohn et al. for automobile
exhaust. They are even lower than the approximate 1:1 ratio reported by Stephens (1973)
for air samples in Riverside, California. The ratios given in Tables 15 and 16 are also
quite variable, which suggests a nonuniform air mass with varying contributions of other
sources compared to automobile exhaust. No distinctive pattern in these variations could
be discerned. If local sources of gasoline vapor are responsible for much of the n-butane,
a recognizable pattern is not to be expected.
3.2.3 Hydrocarbon Data Validity
The analytical group at Washington State University presented some data on
precision, providing in their report (Westberg and Sweany, 1980) comparisons with two
other laboratories on one calibration sample which contained one hydrocarbon (C.H,0;
isomer not stated). Agreement was fair. They also reported an exchange sample study
done with an EPA field laboratory. Complete species breakdown is not given but the
totals and the breakdown by types were in fair agreement.
Another possible comparison is between the sum of individual hydrocarbons indi-
cated by the gas chromatograms and the total measured by an NMHC (non-methane
hydrocarbon) analyzer. Data from such an analyzer (Beckman Instruments Model 6800)
are available, but the NMHC data are given to only one significant figure so this method
hardly provides a useful test. This instrument measures methane and total hydrocarbons
separately -- indeed, on separate samples — and then subtracts to determine NMHC.
-------
Since methane is not small compared to the total hydrocarbon, it is necessary to subtract
a large number from a slightly larger number. This magnifies the error.
Hydrocarbon levels in ambient air can be quite variable, so it is necessary to take
simultaneous samples if agreement is to be expected. Two such replications were
included in the data base; one pair taken in Lancaster, Pennsylvania on August 1*, 1979
(time not stated), and a second pair taken in Downingtown, Pennsylvania, at 0700 to
0800 E5T on August 17, 1979. The. data are shown in Table 17. It should be noted that
these two cities are many miles from Philadelphia, yet hydrocarbon concentrations were
comparable to those in urban air. Automobile exhaust is probably the main source in
these cities. Table 17 follows the format used for the main data table for the Franklin
Institute and industrial site samples. The type distribution gives the percent acetylenes,
olefins, aromatics, and paraffins while the last two columns give total of identified
compounds in ppbC and the sum which includes unidentified compounds. Ethylene is
omitted from these olefin totals for two reasons: to keep the data presentation uniform,
and because the quite high values are suspect although some sort of local source cannot be
ruled out. The two Lancaster samples each showed about 600 ppbC of hydrocarbon with
quite similar type distributions. Even though the two Lancaster samples appear very
similar, some large differences between individual hydrocarbons are apparent. For
example, in Sample 2 the benzene and toluene were about 40% smaller than in Sample 1
but some of the CQ aromatics were larger. The type distributions are reasonably
consistent even though the total hydrocarbon differed by a factor of two between the two
Downingtown samples. The second Downingtown sample contained only half as much
hydrocarbon as the first: concentrations were lower across the board so the type
distribution remained unchanged. There is no ready explanation for the disagreement
between these two samples taken at the same time and place. Successive samples taken
the same morning were similar in composition except for much lower ethylene
concentrations (4 to 6 ppbC instead of 50 to 75 ppbC).
3.2.4 Limitations of Analytical Scheme
The present analytical scheme had some limitations which should be recognized.
-------
Table 17. DISTRIBUTION (%) OF HYDROCARBON SPECIES IN SIMULTANEOUS SAMPLE
PAIRS, TAKEN AT LANCASTER AND DOWNINGTOWN, PENNSYLVANIA,
RESPECTIVELY.
-P
\D
Sample
Number
Type Distribution (%)
Acetylene
Olefin
Aromatic
Paraffin
Total (ppbC)
Identified
Compounds
Including
Unidentified
Compounds
Lancaster, Pennsylvania (time not stated) August 14, 1979
1
2
5
5
11
8
23
25
61
62
487
447
592
552
Downingtown, Pennsylvania (0700-0800 EST) August 17, 1979
1
2
3
2
3
2
32
29
61
66
169
84
205
94
-------
1. Data are limited to hydrocarbons, although oxygenates must be present, some
from atmospheric reactions and some from sources.
2. The ethylene values are all suspect. The operators recognized that many
samples taken near monitoring stations were contaminated by the effluent
from chemiluminescent ozone analyzers. Other samples, not subject to this
fault, showed such high ethylene values that they are hardly believable. The
data summaries omitted.ethylene from the olefin total for the samples subject
to contamination samples but not for others. This introduced a bias into the
data reports. If distributions are to be compared it is better to omit ethylene
for all samples since it cannot be included for all samples. The data have been
recalculated on this basis.
3. Qualitatively, all the hydrocarbons can be attributed to auto exhaust.
Figure 13 shows a total ion chromatograph used to identify hydrocarbon
species seen in field samples. While the chromatograph is not for a sample
from the Philadelphia study, it is characteristic of most of the samples
analyzed and includes the hydrocarbon species in the C<--C1? molecular weight
range observed in the Philadelphia study. The only species listed in Figure 13
with a prominent industrial use is styrene. While information on production
and use of styrene in the Philadelphia area is lacking, it would be most helpful.
Butadiene 1, 3, another prominent industrial hydrocarbon, was not measured.
4. Isoprene, 2 methyl butadiene 1, 3, is shown on the sample chromatogram
(Figure 13) as a well-separated, although very small, peak. However, it was
not included in any of the data reports. This hydrocarbon is important because
it is the parent of the entire terpene series. Isoprene itself, along with alpha
pinene, beta pinene and a host of other terpenes are emitted by vegetation.
As olefinic hydrocarbons they are extremely reactive but this must be
balanced against quite low emission rates. Because the actual size of these
emissions is not accurately known, the role they play in oxidant enhancement
is still controversial. A large family of terpenes, including alpha and beta
pinene, have the formula C1QH16- They would probably appear in the
chromatogram interspersed among the Cg aromatics. They were apparently
not identified on the chromatogram.
-------
TOTAL ION CHfiOMATOGRAM
INCREASING Tine 4ND TEMPERATURE
1. 2 Methyl 1 butene 23.
-2. 2 - Methylbutane 2"*.
3. Halocarbon 25.
14. 1 - Pentene 26.
5. 3 - Methyl 1 butene 27.
6. n Pentene 2S.
7. Isoprene 29.
S. Carbon disuifide 30.
9. t - 2 - Pentene 31.
10. c - 2 Pentene 32.
11. 2 - Methyl - 2 butene 33.
12. 2,2 - Dimethylbutane 34.
13. Cyclopentene 35.
14. (Cyclopentane 36.
V - Methyl 1 Pentene 37.
15. 2,3 - Dimethylbutane 38.
16. /2 Methylpentane 39.
\t 1 - Methyl - 2 pentene 40.
17. c 4 Methyl 2 - pentene 41.
18. 3 - Methylpentane 42.
19. /2 - Methyl 1 - pentene 43.
*• 1 Hexene 44.
20. n - Hexane 45.
21. t - 2 - Hexene 46.
22. ,2 -Methyl 2 - Pentene 47.
v t - 3 - Methyl - 2 - Pentene 48.
c - 2 Hexene 49.
Methylcyclopentane
c - 3 - Methyl - 2 pentene 50.
2,2,3 Trimethylbutane 51.
1,1,1 Trichloroethane 52.
2,4 Dimethylpentane 53.
Benzene 54.
1 - Methylcyciopentene 55.
Cyclohexane 56.
2 - Methylhexane
2,3 - Dimethylpentane 57.
3 - Methylhexane 58.
Dimethylcyclopentane 59.
Dimethylcydopentane 60.
Dimethylcyclopentane 61.
2.2,3, - Tnmetnylpentane 62.
n - Heptane 63.
Methylcyclohexane 64,
Tnmethylcyclopentane 65.
EthylcycJopentane 66.
2,5 - Dimethythexane 67.
2,4 - Dimethylhexane 68.
2,3.4 - Tnmethylpentane 69.
Toluene 7C.
2,3 - Dimethylnexane 71.
2 - Methylheptane 72.
/ 3 - Ethyihexane
^ 3 - Methylheptane
C - 9 Alkane
Dimethylcyclonexane
n - Octane
Ethylcy cione xane
C 9 Alkane
Ethylbenzene
/ p - Xylene
* m - Xylene
Styrene
o - Xylene
n - Nonane
i - Propvibenzene
n - Propvibenzene
3 Etnvitoluene
2 Ethyitolune
1 Ethyltoluene
1,3,5 Trimethylbenzene
1.2,4 Trimethyibenzene
1,2,3 Trimethylbenzene
Methylstyrene
1,3 Dietnylbenzene
1,4 - Diethylbenzene
C 10 Substandard oenzene
C 10 Substandard benzene
FIGURE 13. Total ion chromatograph from ambient air sample (source: Westberg
and Sweany, 1980).
-------
5. The nature of hydrocarbon isomerism introduces a potential bias into
species summation. Thus, there is only one 6-carbon aromatic hydro-
carbon (benzene), and 10 ppbC of this will produce an easily measurable
chromatographic peak. There are seven 6-carbon saturates (counting
cyciohexane and methyl cyclopentane) each of which produces a separate
peak in the chromatogram. There are twenty-two 6-carbon oiefins each
giving a separate peak in the chromatogram. If 10 ppbC of 6-carbon
oiefins were distributed equally among twenty-two peaks, each would
contribute a little less than one-half ppbC. Many would be unmeasurabie
among the larger peaks. This problem becomes more acute at lower
hydrocarbon loading and severe for larger molecules. This "isomer
explosion" not only makes the average concentration at each carbon
number very small, but it also complicates the problem the analyst has in
identifying peaks. It means that the absence of higher oiefins from the
analytical list is partly an artifact.
6. The sample chromatogram in Figure 13 tapers off at molecular weights
above C,Q, suggesting that not too many hydrocarbons are being
overlooked in this range. It is significant that the chromatograms end at
the end of the gasoline range.
-------
4. CASE STUDY DAYS
One of the primary objectives of this study was to recommend days for which data
could be used for model application and validation. The case study days were chosen to
present a variety of situations in which ozone concentrations in excess of 0.12 ppm were
observed. Other factors considered in selecting the case study days included NO2
concentrations, data availability (including EPA-EMSL helicopter data), and wind speed
and wind direction at the surface and aloft during early morning (0400 to 0800 EST), late
morning (0800 to 1200 EST) and afternoon (1200 to 1800 EST) hours. AV selected ten case
study days, with the concurrence of the EPA Project Officer. These days are: 3uly 12,
13, 16, and 19, and August 4, 5, 6, 7, 10, and 22. August 4 through August 7 represents an
episode of high ozone levels.
This section discusses and compares the case study days, particularly with respect to
meteorology, trajectories, transport of ozone and precursors into and within the study
area, pollutant sources, and concentrations aloft.
Synoptic scale trajectories referred to in the following discussions were provided by
the EPA. An atmospheric transport and diffusion model was used to compute the latitude
and longitude of an air parcel at several time intervals prior to its reaching Philadelphia.
The program computes trajectories by taking average winds in the layers of interest from
0000 GMT (1700 EST) and 1200 GMT (0700 EST) wind soundings and, if available,
0600 GMT (0100 EST) and 1800 GMT (1100 EST) soundings. Each observation was
weighted by the inverse of the square of the distance between the parcel and the sounding
station.
Mesoscale trajectories were derived using surface wind information from all sites in
the study area for which data were available. The interpolation scheme uses weighted
averages of the wind components. The weighting factors are inversely proportional to the
square of the distance between the air parcel and the wind site. More weight was given to
wind observations made directly upwind or downwind of the air parcel than when made
removed to one side. This feature is included to reflect the tendency of winds to change
more rapidly in cross-streamline directions than in the along-streamline direction.
-------
For each case study day, mesoscale trajectories were constructed for the following
selected air parcels: (1) an air parcel near downtown Philadelphia at 0600 EST, (2) a
control trajectory approximately 10 miles northwest of downtown Philadelphia at
0600 EST (these were constructed to determine the sensitivity of the starting point on the
trajectory path), (3) an air parcel at an upwind site at 0600 EST, and (4) an air parcel
ending at the site and time of the maximum ozone concentration measured during the day.
Other trajectories were constructed when appropriate.
Rural and urban mixing heights were derived for the case study days for which data
were available. Urban mixing heights were computed from radiosondes released at
Beukers Laboratories in downtown Philadelphia. Detailed temperature profiles were
constructed at 0500, 0900, and 1500 EST for the seven case study days that soundings
were made. The three hours mentioned above are the only times that sufficient data were
available to construct meaningful profiles. From these profiles the height of the base of
the first stable layer (i.e., where the variation of temperature with height is less than the
dry adiabatic lapse rate: 1° C per 100 m) was taken to be the height of the urban mixed
layer. The height of the mixed layer at hours other than 0500, 0900, and 1500 was taken
to be the height at which the temperature profile represented by the dry adiabatic lapse
rate (or moist adiabatic lapse rate, when the air was near saturation) intersected the
detailed profile measured by the temperature sounding. The surface temperature for the
hour of interest and the most recent temperature sounding available (0500, 0900, or 1500)
were used for this determination. In order to minimize the errors involved in extrapo-
lating the 0900 sounding to 1300 and 1400 in this way, the mixing height determined for
1500 EST was used as an upper bound for mixing heights of earlier hours.
The heights of the mixed layer for 0500 through 1800 EST are presented in Table 18
for the case study days. On all days but one, the mixing height was zero meters above
ground level at 0500 EST, signifying a stable layer started at the surface. By 1500 EST
the mixed layer height was usually above 1000 m MSL indicating significant mixing in the
lower atmosphere. The mixing heights usually reached a maximum between 1300 and
1600 EST. At that time, surface temperatures usually began to decrease, causing a
ground-based inversion to form, thus inhibiting mixing from the ground level. The time at
which surface temperatures began to decrease after 1500 is indicated by a zero mixing
height in Table 18. A ground-based inversion began to form by 1800 EST on all of the days
shown.
-------
Table 18. URBAN MIXING HEIGHTS (m MSL) FOR THE CASE STUDY DAYS AS DETERMINED FROM RADIOSONDE
RELEASED FROM DOWNTOWN PHILADELPHIA.
Date
July 19
August 4
August 5
August 6
August 7
August 10
August 22
Hour (EST)
0500
0
0
0
0
0
125
0
0600
187
0
0
0
0
221
0
0700
407
0
0
0
181
291
171
0800
407
0
147
96
250
291
197
0900
741
157
388
345
325
339
411
1000
741
157
424
591*
620
503*
900
1100
851
505
606
591
972
503
900
1200
991
606
606
666
1332
503
1080
1300
1572
698
1072
666
1332
1245
1567
1400
1572
698
1072
666
1332
1516
1567
1500
2314
930
1072
666
1332
1516
1707
1600
2314
1270
1287
1044
1439
0
0
1700
0
1270
1287
0
1439
0
0
1800
0
0
0
0
0
0
0
* Radiosonde "surface" temperature used instead of Franklin Institute.
-------
Rural mixing height information was obtained from AV's acoustic sounder at Summit
Bridge, DE (Site 1). From these data, the time at which surface ozone concentrations
were representative of concentrations aloft was determined in the following way: The
surface-based inversion layer usually begins eroding shortly after sunrise. Heat trans-
ported upward from the surface acts to lift the inversion above the surface at the same
time that it is eroded from below. When the bottom of this elevated inversion layer
reaches the height of the top of the original morning ground-based inversion, some of the
ozone trapped aloft is transported downward. However, the bulk of the ozone reservoir
aloft is not mixed downward until the inversion layer, now elevated, is completely
destroyed. After the destruction of the inversion layer, mixing usually proceeds upward
to the vertical limit of the acoustic sounder (1000 m) in a matter of minutes. The time at
which this thorough mixing within the mixed layer occurs is the time at which surface
ozone concentrations are most representative of concentrations aloft. For the case study
days, the times at which the mixing height first exceeded 1000 m M5L are given in
Table 19. From this table, we can see that, for the case study days, thorough mixing had
occurred by 1100 EST and that the average time of the rural mixing heights exceeding
1000 m is 1000 EST.
A comparison of ozone concentrations at several stations before and after the time
of uninhibited vertical mixing revealed that concentrations were generally low in the
study area before the breakup and became higher afterwards due to mixing of ozone from
aloft. This is supported by the observation that on days when the helicopter was flown,
the surface ozone concentrations just after the inversion breakup were similar to the
concentrations measured aloft by the helicopter. For example, Figure 14 shows an ozone
profile taken over Summit Bridge, DE (Site 1) on August 10 at Q535 EST. The surface
concentration at this site was 0.026 ppm at 0500 EST. The profile indicates concentra-
tions higher than 0.06 ppm in a layer from about 600 to 900 meters MSL. Surface
concentrations at this site increased later as the higher concentrations aloft were mixed
down. At 1000 EST — the first hour when the mixing height was above 1000 meters --
this site recorded a surface concentration of 0.079 ppm.
Information on the locations of the major point sources of volatile organic emissions
within the study area was provided by Philadelphia's Air Management Services. The
majority of these sources are along or close to the Delaware River, with the largest
-------
Table 19. TIME WHEN RURAL MIXING HEIGHTS FIRST EXCEEDED
1000 m AS DETERMINED BY AV ACOUSTIC SOUNDER AT
SUMMIT BRIDGE, DELAWARE (Site 1).
Date
July 19
August 14
August 5
August 6
August 7
August 10
August 22
Time (EST)
1000
0900
0900
0930
0945
1100
0915
-------
2500r
2000
1500
1)
*•*
1)
1000
500
0.02 0.06 0.10 0.14 0.1S
Concentration (ppm)
FIGURE 14. Ozone profile over Summit Bridge, DE (Site 1) at 0535 E5T
on August 10, 1979.
58
-------
concentration of sources in Philadelphia and Chester. These are also areas with heavy
commuter traffic. These sources were considered in the analysis of patterns of high
ozone concentrations.
The hydrocarbon species data set from the Franklin Institute/industrial site provides
data for six of the ten case study days. Although these days were chosen because of
elevated oxidant values, the hydrocarbon species data for these days do not stand out as
distinctive with regard to total concentrations or species distributions.
A resultant wind speed and wind direction vector was derived for each station in the
study area for each of the time periods (early morning, late morning, and afternoon) on
each case study day. From these resultant vectors for each station, then, resultant wind
speed and wind direction vectors were approximated for the entire study area. Table 20
gives, along with peak ozone (OJ and nitrogen dioxide (NO-) concentrations, the surface
resultant wind directions and wind speeds, and average wind speeds and prevailing
directions aloft in the 500- to 1500-m layer, for each of these periods on the case study
days. It also notes whether or not helicopter data were available for each day.
-------
Table 20. PEAK O AND NO CONCENTRATIONS, WIND DATA, AND HELICOPTER DATA AVAILABILITY
FOR CASE STUDYTJAYS FOR THE ENTIRE STUDY AREA.
Date
July 12
July 13
July 16
July 19
August 4
August 5
August 6
August 7
August 10
August 22
Peak
°3
(ppm)
.147
.183
.151
.157
.144
.135
.136
.129
.170
.140
Peak
NO2
(ppm)
.110
.170
.069
.070
.090
.090
.070
.080
.080
.100
Wind Direction
Resultant Surface
Time (EST)
04-08
SW
Var
E
N
NW
NW
NW
N
SW
SW
08-12
W
SE
E
NE
N
N
NW
NE
SW
Var
12-18
NW
Var
SE
SE
N
NW
NW
W
W
SW
Prevail-
ing
Aloft
—
—
NE-E
NE-E
N
N-W
NW
W
W
—
Wind Speed (m/s)
Resultant Surface
Time (EST)
04-08
1.5
1.0
1.0
1.5
1.0
1.5
1.5
1.5
2.5
1.5
08-12
1.5
1.3
1.8
2.5
2.0
2.0
2.0
1.5
3.5
2.0
12-18
3.0
2.0
2.5
1.5
1.0
2.0
2.0
1.5
3.0
2.0
Aver-
age
Aloft
--
—
2.0
4.0
4.0
4.0
3.0
2.0
8.0
—
Avail-
ability
of
Heli-
copter
Data
No
No
No
No
Yes
Yes
Yes
Yes
Yes
No
OS
O
-------
*.l JULY 12, 1979 (THURSDAY)
Important aspects of the July 12 case include the weak influence of the Bermuda
high-pressure cell, indications of significant ozone levels aloft, and high surface ozone
concentrations upwind of Philadelphia. The highest ozone concentration observed this
day occurred downwind of the industrial areas near Wilmington, DE, although high ozone
levels also occurred upwind of the urban complex, indicating long-range transport.
On July 12, 1979, the peak ozone concentration in the study area was 0.147 ppm.
Two of the twelve operating stations reported ozone levels higher than 0.12 ppm and eight
stations reported ozone levels higher than 0.10 ppm. In addition, two stations reported
NO- levels higher than 0.10 ppm.
4.1.1 Synoptic Meteorology
The surface synoptic situation at 0700 EST is shown in Figure 15. Pressure gradients
were weak over the study area and circulation was weakly dominated by the Bermuda
high-pressure cell near the Bahamas. A very moist low pressure cell, the remnants of
Hurricane Bob, was approximately 700 km to the southwest and moving toward the
northeast. Upper level wind flow was westerly and weak.
The synoptic trajectories of air parcels in the 500- to 1000-m and 1500- to 2000-m
MSL layers arriving at Philadelphia at 1300 EST are shown in Figure 16. The paths are
generally from the west and are entirely over land. The urban area of Pittsburgh is near
the path of the 1500- to 2000-m layer parcel.
4.1.2 Mesoscale Meteorology
The mesoscaie flow was weak and from the southwest during the early morning.
Figure 17 shows a streamline analysis depicting the flow across the study area at
0700 EST. At 1100 EST the flow was from the west in the southern part of the study area
but primarily from the northwest at sites north of Philadelphia. During the afternoon, at
1500 EST, most sites were reporting winds from the northwest, with wind speeds at six
sites greater than 5 m/s. Wind speeds were lighter after 1700 EST and primarily from the
west or northwest. No winds aloft data were available.
61
-------
70C
OX
K)
"CURE I;, synoptic situation, 0700 EST, 3uly 12, 1979.
-------
90°
1900 EST°--o
FIGURE 16 Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, July 12, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
FIGURE 17. Streamline analysis depicting surface flow across the study
area at 0700 EST on July 12, 1979. The numbers near the
sites indicate wind speeds (meters per second).
-------
4.1.3 Precursor Patterns
The highest levels of morning precursors occurred downtown, a pattern followed on
all of the case study days; however, concentrations at Lumberton, NJ (Site 3), and
Bristol, PA (Site?), to the east and northeast, respectively, of the Philadelphia urban
area, were abnormally high. The 6:00 to 9:00 a.m. LOT averages of NMHC and NOX>
along with the ratio of iNMHC to NOx are given in Table 21 for rural and urban sites.
From this table, the downtown levels on July 12 were about average when compared to
other case study days. The morning levels at rural sites indicate an interesting pattern.
Low concentrations of both pollutants were measured at Summit Bridge, DE (Site 1), and
Downingtown, PA (Site 2), which are to the southwest and west, respectively, of the
Philadelphia urban area. However, unusually high levels were measured at Lumberton, N3
(Site 3), which is to the east. The 6:00 to 9:00 a.m. LOT average NMHC concentration of
1.0 ppm measured at Lumberton was the highest recorded at this site during the field
program; furthermore, concentrations of NO at this site increased to 0.080 ppm
(0.068 ppm NC^) by 0900 E5T. This pattern of morning precursors is most likely a result
of the airflow which was light and either westerly or southwesterly during the nighttime
and early morning hours (Figure 17). This implies transport of these pollutants from
Philadelphia.
4-1.4 Ozone Patterns
Considering the afternoon flow directions, the areas of highest ozone levels shown in
Figure 18, are as expected. The lowest ozone concentrations occurred near downtown
Philadelphia, probably due to NO scavenging. The highest concentrations were measured
at locations southeast of Philadelphia, with Ancora, NJ (Site 11), recording the maximum
value of 0.147 ppm. Concentrations in excess of 0.10 ppm were recorded by 1100 EST at
Downingtown, PA (Site 11), and remained above this level at Lumberton and Ancora
through 1700 EST.
To determine possible source and impact areas, mesoscale trajectories were
constructed for several air parcels of interest and are shown in Figure 19. A backward
trajectory was developed for an air parcel ending at Ancora, NJ (Site 11), at 1300 EST,
with the highest recorded ozone level of the day, 0.147 ppm. This air parcel followed a
-------
Table 21. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON JULY 12.
Site
No.
1
2
3
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Van Hiseville, N3
6:00 to 9:00 a.m. LDT Averages
N0x
0.00
0.02
0.0*
0.01
NMHC
0.0
0.0
1.0
—
NMHC/NO
Ratio X
—
1.5:1
25.8:1
—
Urban Sites
6
7
8
10
12
13
1*
Chester, PA
Bristol, PA
North Philadelphia Airport, Pfi
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
—
—
0.05
0.12
0.07
0.07
0.10
1.1
1.*
—
—
0.6
—
1.0
—
—
—
—
8.1:1
—
10.0:1
66
-------
1300 EST
1400 EST
1500 E5T
FIGURE IS. Isopleths of ozone at 1300, 1400, and 1500 EST, July 12, 1979.
67
-------
FIGURE 19. Surface trajectory for various air parcels located within the study area on
July 12, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 EST; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
68
-------
trajectory somewhat south of the Philadelphia source area but was close to the highly
industrialized area between Philadelphia and Wilmington, Delaware, at 0600 E5T.
Mesoscale trajectories are also shown for air parcels with high ozone levels at sites
upwind of Philadelphia. Air parcels arriving at Sites 1 and 2 at 1400 EST and 1500 EST,
respectively, contained ozone concentrations in excess of 0.10 ppm. These air parcels
apparently traversed no major source areas during the five to six hours before reaching
the end of the trajectory, indicating the possibility of longer-range transport, particularly
in light of the long over-land synoptic trajectory previously shown in Figure 15. The
evidence of transport aloft is discussed below.
An air parcel beginning at downtown Philadelphia at 0600 EST was located between
Lumberton, NJ (Site 3), and Van Hiseville, NJ (Site 5), at 1500 EST. These stations had
high O, concentrations of 0.124 and 0.105 ppm, respectively, at this time.
4.1.5 NO-, Patterns
Peak NO_ concentrations occurred near the urban area, very late in the evening.
Conversion of O, into NO^ by scavenging of NO (relatively plentiful in the urban area) is
the probable cause. For example, the Franklin Institute (Site 13) NO2 peak of 0.090 ppm,
which occurred at 2100 EST, followed an ozone concentration trend of 0.070 to 0.020 to
0.000 ppm from 1900 EST to 2100 EST.
4.1.6 Concentrations Aloft
Although no helicopter data were available for July 12, pollutant concentrations at
upwind surface stations at the estimated time of morning inversion breakup were
reviewed to get some idea of ozone and precursor transport aloft. No acoustic sounder
data were available to determine the exact time of inversion breakup, so 1000 EST was
assumed, based upon the fact that all but one of the case study days for which acoustic
sounder data were available experienced the first hour of uninhibited vertical mixing at
1000 EST.
69
-------
The diurnal profiles of ozone for the upwind sites at Summit Bridge, DE (Site 1) and
Downingtown, PA (Site 2), for July 12 are shown in Figure 20. A rapid morning ozone
build-up, characteristic of mixing from aloft, is evident. At 1000 EST, Summit Bridge and
Downingtown recorded ozone concentrations of 0.068 ppm and 0.075 ppm, respectively,
suggesting significant ozone transport aloft. NO and NMHC concentrations were near
zero at this time suggesting no significant precursor transport. Transport of such levels
of ozone helps explain the high afternoon ozone concentrations recorded at Sites 1 and 2
(0.109 and 0.114 ppm, respectively) despite their positions predominantly upwind of
Philadelphia.
70
-------
Downingtown, PA
(Site 2)
Summit Bridge, DE
(Site i)
0.00
0200
0600
1000 1*00
Time (E5T)
1800
2200
FIGURE 20. Diurnal profiles of ozone at upwind sites on July 12, 1979.
71
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4.2 JULY 13, 1979 (FRIDAY)
Important aspects of the July 13 case include the highest ozone and NO2 concentra-
tions recorded during the field program, variable flow, and indications of a reservoir of
elevated ozone concentrations aloft. Peak concentrations were due to the influence of
the urban plume, coupled with near stagnation and ozone mixed down from aloft.
The peak O, and NO2 concentrations recorded during the field program (0.183 and
0.170 ppm, respectively) occurred on July 13. Ten of the thirteen operating stations
reported O, levels higher than 0.12 ppm and four stations recorded NO2 concentrations
higher than 0.10 ppm. July 13 followed another case study day (July 12) during which high
NO_ and O-, levels were observed.
4.2.1 Synoptic Meteorology
The surface synoptic pattern is depicted in Figure 21. The Bermuda high-pressure
cell, about 500 km east of Florida, exerted a weak influence over the study area. The
remnants of Hurricane Bob were 700 km west-southwest of the study area, moving
eastward. These two features were reflected in the upper-level flow which was very
weak and primarily northwesterly over the study area.
The trajectories of air parcels traveling in the 500- to 1000-m and 1500- to 2000-m
layer toward Philadelphia (arrival time 1300 EST) are shown in Figure 22. The paths are
very similar to the synoptic trajectories for July 12, which is reasonable, considering the
stability of the weather systems. The path brings the 500- to 1000-m parcel near the high
emission density area of Washington, D.C.-Baltimore less than 36 hours upstream and
provides a continual over-land trajectory with slight anticyclonic curvature.
4.2.2 Mesoscale Meteorology
Early morning wind flow was variable and very weak. Late morning southeasterly
wind flows were primarily weak; however, a great deal of variability was evident. In the
afternoon, there was a significant spatial variation in the wind speed, with some stations
reporting calm winds and some stations reporting winds in excess of 5 m/s; however, most
stations reported wind directions with a southerly component.
72
-------
70'
90
80° 75°
FIGURE 21. Synoptic situation, 0700 EST, July 13, 1979.
-------
FIGURE 22.
Synoptic trajectory of air parcels arriving at Philadelphia at 1300 E$T, July 13, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
The weak and variable wind flow at the surface, coupled with relatively little
movement of air parcels on the synoptic scale (Figure 21) between 0100 and 1300 EST,
indicates that July 13 was a case of near stagnation.
4-2.3 Precursor Patterns
Urban precursor levels were elevated while rural areas had characteristically low
concentrations. Maximum morning NO and NMHC concentrations at urban stations were
in excess of 0.10 ppm and 1.0 ppm, respectively, with 3.5 ppm of NMHC recorded at
Chester (Site 6) at 0600 EST. The 6:00 to 9:00 a.m. LOT averages of NMHC and NOx,
along with the ratio of NMHC to NO are given in Table 22 for rural and urban sites.
X
Elevated levels of both pollutants were recorded at the urban sites, whereas levels at
outlying rural stations were generally very low. Chester, PA (Site 6), measured the
highest average NMHC level (2.6 ppm) and also reported relatively high levels (0.040 to
0.056 ppm) of NO2 from 6:00 to 9:00 a.m. LOT.
The elevated precursor levels measured at these urban and near-urban sites were
above normal and generally above levels observed on other case study days. This, coupled
with the near-stagnant weather situation on this day, helps to explain the unusually high
ozone concentrations which occurred along the fringe of the urban area.
4.2.4 Ozone Patterns
Isopieths of ozone concentrations at 0900, 1100, 1200, and 1300 EST are shown in
Figure 23. By 0900 EST, a concentration of 0.101 ppm was already recorded at
Ancora, NJ (Site 11), southeast of Philadelphia, while concentrations were less than
0.04 ppm downtown. After this, highest ozone concentrations were centered near the
urban area. At 1100 EST, ozone concentrations in excess of 0.12 ppm were evident at
Chester, PA (Site 6), Camden, NJ (Site 10), and Ancora, NJ (Site 11), the first two of
which are near urban sites. Thus, high levels were widespread very early, although
downtown sites were still low. Downingtown, PA (Site 2) and Lumberton, NJ (Site 3), west
and east of Philadelphia, respectively, were recording ozone levels in excess of 0.10 ppm.
The following hour (1200 EST), the highest level recorded during the program, 0.183 ppm,
occurred at Chester. At 1300 EST,Camden, NJ (Site 10), had the highest ozone
75
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Table 22. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON JULY 13.
Site
No.
1
2
3
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Van Hiseville, NJ
6:00 to 9:00 a.m. LOT Averages
N0x
0.00
0.0*
0.03
0.02
NMHC
0.1
0.2
0.3
—
NMHC/NO
Ratio
0.0:0
5.8:1
11.0:1
—
Urban Sites
6
10
12
13
1*
Chester, PA
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
—
0.17
0.17
0.15
0.12
2.6
—
0.9
—
1.2
—
—
5.5:1
—
10.2:1
76
-------
0900 EST
1200 EST
1300 EST
FIGURE 23. Isopleths of ozone at 0900, 1100, 1200, and 1300 EST, July 13, 1979.
77
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concentration (0.161 ppm), but the entire metropolitan area of Philadelphia also had
relatively high ozone levels (greater than 0.110 ppm). Moreover, high ozone levels were
measured at Sites 2, 3, 8, and 11 as well. Ozone levels persisted in excess of 0.12 ppm
until late afternoon at some locations.
Surface mesoscale trajectories were developed to help determine the origin of some
of the observed high ozone concentrations. These trajectories are shown in Figure 24.
The flow was weak and variable with a tendency towards southerly and southeasterly
winds, particularly in the late morning and afternoon.
An air parcel beginning at Philadelphia at 0600 EST was about 20 km east of
Downington, PA (Site 2), at 1300 EST. Unfortunately, this is an area for which no data
were available; however, this parcel is between Downingtown, PA (Site 2), and the
AMS Lab, Philadelphia (Site 14). These two sites reported ozone levels of 0.123 and
0.140 ppm, respectively, at this time, and we might expect even higher levels along the
path of the trajectory.
Chester, PA (Site 6), as discussed above, had the highest ozone concentration
measured on this day and recorded a value of 0.183 ppm at 1200 EST. A parcel ending at
this site and time followed a trajectory from the southeast and started (0600 EST) in an
area of expected low precursor concentrations 20 km south-south west of Philadelphia's
central business district.
Air parcels with high ozone levels at 1400 EST at the AMS Lab, Philadelphia
(Site 14), and 1500 EST at Lumberton, N3 (Site 3), began in the eastern portion of the
study area. In fact, the air parcel ending at the AMS Lab at 1400 EST began very near to
Lumberton at 0600 EST. The NMHC and NO concentrations at Lumberton at that time
were both zero, indicating another high ozone parcel originating in areas of low precursor
levels.
A re-examination of the ozone isopleths shown in Figure 23 indicates that the
surface mesoscale trajectories do not tell the whole story. The center of high ozone
concentrations does not move westward across the study as the mesoscale trajectories
imply, but rather shows the spreading out tendency characteristic of a stagnation day.
The contribution of ozone transport aloft to this process is discussed below.
78
-------
FIGURE 2^. Surface trajectory for various air parcels located within the study area on
July 13, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions oi the parcels at one hour
intervals.
79
-------
A comparison of the mesoscale trajectories with the synoptic trajectories shown in
Figure 22 implies some wind shear aloft, since the air parcels approach from different
quadrants. However, the variability of the surface winds and the fact that the synoptic
trajectories may be based solely upon 0700 EST and 1700 EST winds aloft make this
implication speculative.
it.2.5 NO2 Patterns
NO? concentrations were generally higher on this day at all sites than on other case
study days. Peak concentrations in excess of 0.10 ppm (including the highest value of the
entire program, 0.17 ppm) were recorded at urban and near-urban sites in the late
morning. South Broad Street (Site 12) recorded concentrations in excess of 0.10 ppm all
day. These concentrations were apparently the result of NO reactions with the very high
ozone levels observed even in the urban areas.
4.2.6 Concentrations Aloft
From the above discussion, it is evident that areas both upwind and downwind of
Philadelphia experienced high ozone levels. The site which experienced the highest
observed levels — Chester, PA (Site 6) — was not directly downwind as determined by
surface flow. Thus, in light of the high levels observed at the upwind stations at
Ancora, NJ (0.141 ppm), and Lumberton, NJ (0.125 ppm), possible explanations are that
there was some contribution of long-range transport and/or, since high levels were
observed the previous day, there was some carryover or buildup. Unfortunately, no
helicopter data are available for that day to assess ozone concentrations aloft prior to
inversion breakup. However, a review of concentrations at upwind sites (taken to be to
the east, in this case) during the first hour after thorough mixing can provide an indication
of ozone levels aloft. Based upon acoustic sounder data obtained for other case study
days (no such data are available for July 13), 1000 EST is a good approximation of this
first hour of mixing, and the concentrations shown in Figure 25 are consistent with this.
Ozone concentrations of 0.097 ppm at Lumberton, NJ (Site 3), 0.064 ppm at
Van Hiseville, NJ (Site 5), and 0.123 ppm at Ancora, NJ (Site 11), were observed at
1000 EST. At the time of mixing, these ozone levels were some of the highest observed
during the program, implying a substantial ozone reservoir aloft on July 13. The effect of
80
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0.20
0.18
0.16
7 0-14
5.
0.
I 0.12
*j
Ifl
5 0.10
u
5
U
-------
mixing of ozone aloft down to the surface is further illustrated in Figure 25, showing
diurnal profiles of ozone at Chester and several upwind sites. Very rapid increases in
ozone levels are evident after mixing begins.
82
-------
^•3 JULY 16, 1979 (MONDAY)
Important features of the July 16 case include southeasterly flow, confinement of
high ozone concentrations to areas downwind of Philadelphia, and an unusual over-the-
water synoptic air parcel trajectory. High ozone levels were due primarily to emissions
from the greater Philadelphia urban area.
The peak ozone level on July 16 was 0.151 ppm. Three of the twelve operating
stations recorded levels higher than 0.12 ppm. All other sites recorded 0.10 ppm or less.
NC>2 levels were also fairly low. The peak NO2 concentration was 0.069 ppm with three
stations reporting concentrations in excess of 0.05 ppm.
4.3.1 Synoptic Meteorology
The synoptic situation is shown in Figure 26. A weak, slow-moving cold front was to
the northwest, while the wind flow was dominated by a sluggish low pressure center to the
southeast, bringing primarily east to southeast flow over the study area. Upper level flow
was extremely weak with little pressure gradient evident. Also, thundershowers were
present in the study area in the afternoon.
The synoptic trajectory (Figure 27) shows an air parcel in the 500- to 1000-m layer
arriving from the southeast, resulting in an over-water trajectory, not normally conducive
to high ozone concentrations in the study area. The air parcel in the 1500- to 2000-m
layer approached more from the southwest, although it also spent the last hours of its
journey over the ocean.
4.3.2 Mesoscale Meteorology
Surface airflow over the study area was characterized by an easterly component
throughout the day. During the morning hours, sites near the urban areas, as well as to
the west and southwest of Philadelphia, reported winds primarily from the east. However,
sites to the northeast showed a wider variation: some sites reported winds from the
southeast, while others reported winds from the northeast. Wind speeds remained less
than k m/s at all sites prior to 1200 EST. During the afternoon, winds were stronger and
83
-------
OO
-p-
1024 A CHICAGO* mm
FIGURE 26. Synoptic situation, 0700 EST, 3uly 16, 1979.
-------
Go
45'
90
TO"
FIGURE 27. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, July 16, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
primarily from the southeast over the entire study area. By 1900 E5T, some sites were
reporting winds from the north or northeast. Winds aloft, as indicated by pibal data at
Wilmington, Delaware, and Trenton, New Jersey, were primarily easterly or southeasterly
through 2000-m throughout the day.
4.3.3 Precursor Patterns
Morning precursor concentrations were generally lower at all sites than those
observed on any other case study day, although no downtown NMHC data were available.
The 6:00 to 9:00 a.m. LOT averages of NMHC and NOx, along with the ratio of NMHC to
NO , are given in Table 23 for rural and urban sites. The AMS Lab (Site 14) in
Philadelphia, within 9 km of the central business district, reported 6:00 to 9:00 a.m. LOT
average concentrations of 0.2 ppm for NMHC and 0.03 ppm for NO .
A
4.3.4 Ozone Patterns
Ozone concentrations were low at all sites during the morning hours except for
Downington, PA (Site 2), west of Philadelphia. This site reported ozone concentrations
exceeding 0.08 ppm by 1100 EST. Through the afternoon, concentrations remained low at
all sites upwind of the urban area, as shown in Figure 28, which also shows isopleths of O,
concentrations at 1200, 1300 and 1400 EST. (Data were obtained for this figure from sites
which did not participate in the study but which were downwind under this unusual flow
regime.) This figure shows a broad area of elevated O, extending from the edge of the
urban and industrial areas downwind of Philadelphia. Chester, PA (Site 6), and Clay-
mont, DE (Site 15), although not directly downwind of Philadelphia, reported daily
maximum ozone concentrations of 0.131 and 0.130 ppm, respectively, at 1400 EST. Since
wind speeds were generally less than 5 m/s throughout the day, and since ozone levels
aloft appear to be low on this day (as evidenced by the low daily maximum concentrations
at the upwind sites of Lumberton, NJ (Site 3), Ancora, N3 (Site 11), and Van Hiseville, NJ
(Site 5) of 0.058, 0.061, and 0.061 ppm, respectively), the high levels at Chester and
Claymont are likely due to industrial/automotive emissions within 20 km of the sites. The
region of elevated ozone concentrations shown on Figure 28 persisted through 1700 EST.
86
-------
Table 23. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FO&
RURAL AND URBAN SITES ON JULY 16.
Site
No.
1
2
3
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumber ton, NJ
Van Hiseville, N3
6:00 to 9:00 a.m. LOT Averages
NOX
0.00
0.03
—
0.01
NMHC
0.0
0.1
0.1
—
NMHC/NO
Ratio X
—
4.3:1
—
—
Urban Sites
10
13
14
Camden, NJ
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
0.04
0.04
0.03
—
—
0.2
—
—
6.7:1
87
-------
1200 EST
1300 EST
1*00 EST
FIGURE 28. Isopieths of ozone at 1200, 1300, and 1400 EST, July 16, 1979.
88
-------
The surface trajectories for this day shown in Figure 29 indicate that
Downingtown, PA (Site 2), was downwind of Philadelphia. An air parcel beginning at
0600 EST in downtown Philadelphia was slightly northwest of Downingtown, PA (Site 2), at
1500 EST. (Site 2 recorded the highest study area ozone concentration at this time.) The
parcel followed an eastward path during the morning until winds from the southeast
became dominant in the afternoon, then the parcel traveled in a northwest-only direction.
An air parcel ending at Chester, PA (Site 6), at 1400 EST with a concentration of
0.131 ppm was 40 km southeast of Philadelphia at 0600 EST, although it passed over highly
industrialized areas prior to its arrival at Chester.
4.3.5 NO., Patterns
July 16 experienced the lowest NCX concentrations of any of the case study days.
The peak concentration of 0.069 ppm occurred at Chester, PA (Site 6), at 2300 EST,
reflecting the late evening decomposition of ozone. The other two sites recording levels
greater than 0.050 ppm (Claymont, DE and Franklin Institute, PA) also reported the
2300 EST peaks.
4.3.6 Concentrations Aloft
Although no pollutant measurements were recorded above the surface level on this
day, upwind surface concentrations recorded at 1000 EST indicate that ozone levels aloft
were lower than on the first two case study days discussed. (No acoustic sounder data
were available for July 16. 1000 EST was selected as the first complete hour of mixing
through 1000 m, based upon acoustic sounder data on other case study days.) Observed
concentrations were 0.049 ppm for ozone, 0.000 ppm for NO, and 0.000 ppm for NMHC at
Lumberton, NJ (Site 3), and 0.061 ppm of ozone and 0.002 ppm of NO at Van Hiseviile, NJ
(Site 5). Diurnal profiles of ozone at Lumberton, NJ (Site 3), and Van Hiseviile, NJ
(Site 5), in Figure 30 demonstrate the relatively low ozone levels observed all day upwind
of Philadelphia. This indication of lower levels aloft is consistent with the observation
that high ozone concentrations were much less widespread and occurred downwind of
Philadelphia on July 16.
89
-------
FIGURE 29. Surface trajectory for various air parcels located within the study area on
July 16, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
90
-------
0.18f
0.16-
s
30.12
0.10
O.OS
0.04
0.02
0.00
Van Hiseviile, NJ
/ (Site 5)
0100
0500
0900 1300
Time (EST)
1700
2200
FIGURE 30. Diurnal profiles of ozone at upwind stations on July 16, 1979.
91
-------
4.4 JULY 19, 1979 (THURSDAY)
The important aspects of the July 19 case were southeasterly flow, the apparently
long residence time over the New York City area of a low-level air parcel arriving at
Philadelphia at 1300 EST, indications of high concentrations of ozone transported aloft,
and some NO transport at the surface. Peak ozone concentrations resulted from both the
greater Philadelphia urban plume and transport aloft.
The peak ozone concentration recorded on July 19 was 0.160 ppm. Six of the
thirteen operating stations reported ozone concentrations equal to or greater than
0.12 ppm and an additional four stations reported ozone concentrations equal to or greater
than 0.10 ppm. The peak NO2 concentration was 0.070 ppm, with six stations reporting
NC>2 concentrations equal to or greater than 0.05 ppm.
4.4.1 Synoptic Meteorology
On July 19, a broad, high-pressure cell dominated the northeastern United States,
including Philadelphia, as shown in Figure 31. This high pressure cell was to the west
bringing flow with an easterly component to the study area. A stationary front, which had
been present for several days, was about 150 km to the southeast. The upper level flow
was predominantly west-southwesterly.
The 100- to 500-m and 1500- to 2000-m layer synoptic air parcel trajectories
depicting the 96-hour paths of parcels arriving at Philadelphia at 1300 EST are shown in
Figure 32. The 100- to 500-m trajectory shows a very erratic path, as might be expected
considering the long-term presence of the stationary front mentioned above. The
trajectory indicates a prolonged residence time in the vicinity of the New York City
metropolitan area.
The 1500- to 2000-m trajectory is quite different. It is a long over-land trajectory
traversing the Great Lakes area. Since the maximum mixing height on July 19 in
downtown Philadelphia was greater than 2000 m MSL, transport at both levels may be
important.
92
-------
451
40'
90
FIGURE 131. Synoptic situation, 0700 EST, July 19, 1979.
-------
FIGURE 32. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, 3uly 19, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
4.4.2 Mesoscale Meteorology
Surface wind flow veered from northerly to northeasterly to southeasterly from
early morning to late afternoon. Several sites (North Philadelphia Airport, Philadelphia
International Airport, Greater Wilmington Airport, Delaware, Trenton-Mercer County
Airport, New Jersey, and Downingtown, Pennsylvania) reported wind speeds greater than
2.0 m/s from 0500 EST through 2100 EST, indicating some significant wind flow was
prevalent all day. Winds aloft veered from northeasterly to easterly. The overall wind
flow patterns were very similar to those on July 16 discussed previously.
Mixing heights on this day were the highest of all of the seven case study days for
which data were available (see Table 18). Rural acoustic sounder data show uninhibited
mixing (mixing through 1000 m) at 1000 EST with strong vertical mixing generally
confined to lower layers throughout the day. Urban mixing heights, as determined from
radiosonde observations, were 741 m at 0900 EST and 2314 m at 1500 EST.
4.4.3 Precursor Patterns
The 6:00 to 9:00 a.m. LOT NMHC and NO averages along with the NMHC to NO
A X
ratios are given in Table 24 for rural and urban sites. Urban morning precursor
concentrations were quite low and NO concentrations at outlying stations were even lower
(<0.025 ppm), with the exception of Van Hiseville, NJ (Site 5), 75 km east-northeast of
Philadelphia, which recorded a 6:00 to 9:00 a.m. LOT NO average of 0.08 ppm, the
A
highest morning concentration observed at this site during the program. The high
concentration of NO observed at Van Hiseville (Site 5) and the synoptic trajectory
discussed previously raise the possibility of surface precursor transport. This is supported
by peroxyacetyi nitrate (PAN) data at Van Hiseville on this day, presented in Figure 33.
Concentrations of this pollutant, a product of the photochemical process, reached
3.70 ppb at 1000 EST, whereas the July average for this hour is 1.4 ppb. Early morning
flow at the surface was from the north or northeast in the northern section of the study
area, which suggests some transport from the New York City metropolitan area.
95
-------
Table 24. 6:00 to 9:00 a.m. LDT (0500-0800 E5T) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON 3ULY 19.
Site
No.
1
2
3
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Van Hiseville, N3
6:00 to 9:00 a.m. LDT Averages
N0x
0.02
0.02
0.05
0.08
NMHC
0.3
0.0
0.4
—
NMHC/NO
Ratio X
16.5:1
—
8.6:1
-—
Urban Sites
6
7
8
10
12
13
14
Chester, PA
Bristol, PA
North Philadelphia Airport, PA
Camden, N3
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
—
—
0.03
0.07
0.05
0.05
0.03
0.7
1.4
—
—
0.2
—
0.4
—
—
—
—
3.4:1
—
12.3:1
96
-------
^.20
0.20-
0800
1000
1200
Time (EST)
1400
1600
FIGURE 33- Diurnal profiles of PAN at Van Hiseviile, N3 (Site 5) on July
19, 1979 and July average.
97
-------
i*.i*.i* Ozone Patterns
Ozone isopleths for the study area at 1400, 1500, and 1600 EST are shown in
Figure 34. As on July 16, a day in which the surface study area flow was from the
southeast, a broad area of elevated ozone was located west and southwest of Philadelphia.
Summit Bridge, DE (Site 1), Downingtown, PA (Site 2), Claymont, DE (Site 15), and
Chester, PA (Site 6), all reported ozone concentration of 0.120 or higher by 1400 EST.
The highest ozone concentration of the day (0.160 ppm) was found at Claymont, DE
(Site 15), southwest of Philadelphia, at 1600 EST. During the day, urban and near-urban
sites also reported high concentrations. Sites to the east and southeast reported lower
peak concentrations.
Surface trajectories for this day are shown on Figure 35. During the early morning
hours, winds were from the north or northeast; by 1100 EST, the flow was from the east,
and during the afternoon the flow was from the southeast. A parcel starting at 0600 EST
in downtown Philadelphia was about eight miles west of Downingtown, PA (Site 2), at
1500 EST when a 0.157 ppm ozone concentration was recorded. As discussed above, the
maximum ozone concentration recorded in the study area during this day was 0.160 ppm
at Claymont, DE (Site 15), at 1600 EST. Figure 35 shows a parcel ending at this site and
time with a trajectory beginning far to the east making an anticyclonically-curved path to
arrive at the site from the southeast. The 0600 EST starting point was over an area
closest to Lumberton, N3 (Site 3). Peak morning NO and NMHC levels at Lumberton, N3
(Site 3), were 0.024 ppm and 0.5 ppm, respectively, higher than normal for this site and
generally higher than other rural sites.
Mesoscale surface trajectories were also developed for two cases in which high
ozone levels were reported downtown and to the east. The 0600 EST position of an air
parcel arriving at the AMS Lab, Philadelphia (Site 14), at 1300 EST, with an ozone
concentration of 0.130 ppm, was near the near-urban station of Bristol, PA (Site 7). An
air parcel arriving at Lumberton, N3 (Site 3), at 1100 EST with a 0.104 ppm ozone
concentration was 45 km to the northeast at 0600 EST near the rural Robbinsville, NJ
(Site 4), station. Such elevated ozone levels at a site upwind of Philadelphia suggest
long-range ozone transport, particularly in light of the synoptic trajectory shown in
Figure 32.
98
-------
1*00 EST
500 EST
1600 EST
FIGURE 34. Isopieths of ozone at 1*00, 1500, and 1600 EST, July 19, 1979.
99
-------
.104 ^^
Site 3
1100 E5T
FIGURE 35. Suriace trajectory for various air parcels located within the study area.on
July 19, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 EST; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
100
-------
4.*.5 NO2 Patterns
The peak NO2 concentration (0.070 ppm) occurred at Claymont, DE (Site 13),
southwest of Philadelphia. This and other sites recording NG>2 values in excess of
0.05 ppm were primarily downtown and to the southwest (downwind), and nearly all peaked
in the late morning. NC>2 peaks downwind of the urban area in the late morning are the
characteristic result of the NO/O-j reaction and preceed the afternoon ozone buildup.
Bristol, PA (Site 7), to the northeast, also recorded NO? concentration in excess of
0.05 ppm. Van Hiseville (Site 5), east-northeast of Philadelphia, recorded 0.046 ppm at
0800 EST, the highest NCu concentrations recorded there during the field program, a
reflection of the high NO concentrations observed during the hours preceding 0800 EST.
4.4.6 Concentrations Aloft
The combination of ozone transport aloft and surface precursor transport is a
plausible explanation for the high NO- levels observed at Van Hiseville, NJ (Site 5), and
the high ozone levels observed at Lumberton, N3 (Site 3), both upwind of Philadelphia.
Data from direct measurement of pollutants aloft were not available. Mixing height
data collected at Summit Bridge, DE (Site 1), indicated that the first full hour of mixing
to 1000 m was at 1000 EST. Ozone and NO pollutant measurements at the upwind sites of
Lumberton, NJ, and Van Hiseville, NJ (Sites 3 and 5), at this time were 0.082 and
0.083 ppm, and 0.005 and 0.003 ppm, respectively. The diurnal profiles of ozone and NO
at these two upwind locations presented in Figure 36 show these indications of transport.
The rapid increase in ozone and concurrent rapid decrease in NO are characteristic of
ozone aloft being mixed down. This suggests that high levels of ozone were transported
aloft and that there was very little transport of precursors aloft. However, as discussed
above, the abnormally high 6:00 to 9:00 a.m. NO concentrations observed in the eastern
.X
portion of the study area implies surface precursor transport,
4.4.7 Hydrocarbon Species Data
Both samples collected at Franklin Institute and the industrial site had NMHC below
the overall average on this day, which is consistent with the fact that mixing heights were
101
-------
o.os
a.
a.
o
0.06
g 0.04
4)
U
U 0-02
O
z
0.00
NO
Van Hiseviile, N3
/ (Site 5)
Lumberton, PA
(Site 3)
0300
0700
1100
1300
1900
2300
0.12
± 0.10,
o
2 0.08
4*
C
-------
fairly high in the morning hours. The species breakdown showed differing unusual
features:
1. The Franklin Institute samples, in addition to the background of automobile
exhaust hydrocarbons, showed C7-Co paraffins in unusual amounts. Methyl
cyclohexane, which showed large amounts in several samples, was 70 ppbC in
the 0500 to 0600 E5T sample and somewhat elevated at 0700 to 0800 EST.
2. The industrial site samples did not have unusual amounts of this hydrocarbon
but showed unusually high concentrations of iso-propylbenzene (cumene). This
is an industrially important hydrocarbon, so this might reflect a chance spill of
this hydrocarbon.
103
-------
4.5 AUGUST 4, 5, 6, 7, 1979 (SATURDAY, SUNDAY, MONDAY, TUESDAY)
These days represent the only extended ozone episode observed during the monitor-
ing period. August 4 was interesting because it was a weekend day with high observed
ozone. The highest concentrations appeared to be transported into the study area from
the north, and a low-level surface trajectory brought the parcel up along the Atlantic
seaboard. August 5, another weekend day (Sunday), had the following interesting
characteristics: (1) peak ozone concentrations directly downwind of Philadelphia; (2)
indications of significant early morning ozone concentrations aloft; and (3) a long,
over-land synoptic trajectory. August 6 was remarkably similar to August 5 with similar
ozone patterns, indications of transport, and air parcel trajectories. August 7 demonstra-
ted significant wind shear, very little early morning ozone aloft, and surface flow reversal
during the day.
This four-day series represented an extended episode period in which ozone
concentrations in excess of 0.120 ppm on each day were recorded within the study area.
Table 25 gives the maximum ozone and NO- concentrations and the number of sites
exceeding certain levels on the four days. This table shows that, although peak ozone
concentrations were fairly high on each of the four days, the number of stations
experiencing high ozone concentrations did not increase from day to day during the
episode; furthermore, high ozone concentrations were less widespread than on most of the
other case study days. Peak NG>2 concentrations were less than 0.10 ppm, as was the case
for all but two of ten case study days examined.
4.5.1 Synoptic Meteorology
Figures 37a through 37d show the surface synoptic progression for the four days. A
high-pressure cell was centered just to the southwest of the study area on August 4 and
became stronger so that most of the eastern half of the United States was dominated by a
high-pressure ceil during the days following. A surface front situated off the coast of the
northeastern states on August 4 underwent frontolysis on August 5. A weak cold front
just north of the Great Lakes on August 5 moved through the study area on August 6.
104
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Table 25. MAXIMUM OZONE AND NO? CONCENTRATIONS OBSERVED
IN THE STUDY AREA DURING THE PERIOD AUGUST *
THROUGH AUGUST 7, 1979.
Date
August 4
August 5
August 6
August 7
Ozone
Concen-
tration
(ppm)
.m
.135
.136
.129
Number of Sites >
0.12 ppm
3
2
3
3
0.10 ppm
6
5
5
5
NO2
Concen-
tration
(ppm)
.090
.090
.07*
.080
Number
of Sites
_>0.05 ppm
5
6
5
5
105
-------
o
ON
FIGURE 37a. Synoptic situation, 0700 EST, August 4, 1979.
-------
FIGURE 37b. Synoptic situation, 0700 EST, August 5, 1979.
-------
-70°
o
00
45 °J
40
90
45'
40"
FIGURE 37c. Synoptic situation, 0700 EST, August 6, 1979.
-------
FIGURE 37d. Synoptic situation, 0700 EST, August 7, 1979.
-------
It is interesting to note that a similar synoptic pattern and sequence of weather
events was also associated with the only extended episode situation observed during a
similar 1978 study in Philadelphia (Chan et al., 1979).
The approach of air parcels to the study area became more northerly as the episode
progressed. Figures 38a through 38d show the synoptic trajectories of air parcels arriving
at Philadelphia at 1300 E5T on August 4 through 7, respectively. On August 4, the 100- to
500-m and 1500- to 2000-m layer trajectories were quite different. The path followed by
the 100- to 500-m parcel was erratic and included a long, over-land trajectory along the
Atlantic seaboard. The path followed by the 1500- to 2000-m layer parcel was overland
and from the west. On the last three days of the episode, the 100- to 500-m layer parcels
followed anticycionically-curved paths approaching from the west, northwest, and then
north of Philadelphia. The lower-level air parcel arriving on August 4 appeared to have
traversed the high emission density areas of Baltimore and Washington, D.C., while
parcels arriving on August 5 and 6 did not directly traverse any major source area but
traversed areas near the major urban centers of Cincinnati, Cleveland, and the lower
Great Lakes. The lower-level trajectory ending on August 7 approached through the New
York City area.
4.5.2 Mesoscale Meteorology
The general surface study area flow was north to northwest on August 4 and was
predominantly from the northwest on August 5 and 6. On August 7 the flow was from the
northeast in the morning but from the southwest during the afternoon.
Upper air wind flow over the study area was generally northerly on August 4 through
the morning of August 5, backing to westerly in the afternoon of August 5. Northwesterly
flow aloft prevailed on August 6 and westerly on August 7.
Urban mixing heights on August 4 through 6 were the lowest of any of the seven
case study days for which data were available (see Table 18). Mixing heights on August 4
were particularly low. The 0900 EST mixing height was 157 m and urban mixing heights
remained under 1000 m most of the day. The maximum urban mixing heights on August 4,
5, 6, and 7 were 1270 m, 1287 m, 1044 m and 1439 m, respectively. Rural mixing height
110
-------
75'
FIGURE 38a. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 4, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
N>
FIGURE 38b. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 5, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
90
80C
75
FIGURE 38c. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 6, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
FIGURE 38d. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 7, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
data, as determined from the Summit Bridge, DE (Site i), acoustic sounder records
indicate that rural mixing heights exceeded 1000 m on ail days during the episode and
reached this level between 0900 and 1000 EST. However, analysis of the acoustic sounder
traces reveals that the intensity of mixing ranged from weak to very weak on August 4, 5,
and 6. The intensity of mixing within the mixed layer is related to "thermal roots"
appearing on acoustic sounder traces. Thermal roots appear on acoustic sounder traces as
vertical spikes that taper with height. They are typical of free convection conditions
(after the breakup of the ground-based inversion) with light winds and strong radiational
heating (Baxter et ah, 1978). The degree of mixing is a function of both the darkness and
vertical extent of the thermal roots. The vertical extent of the thermal roots for
August 4, 5, 6, and 7 after the surface-based inversion was lifted is given in Table 26.
The table shows that, while mixing occurred through the 1000 m level, it was not vigorous
and thermal roots displayed little vertical extent, seldom exceeding 300 m. Vertical
mixing on August 7 was somewhat more vigorous in comparison to the other case study
days.
4.5.3 Precursor Patterns
The 6:00 to 9:00 a.m. LOT averages of NMHC and NO , along with the ratio of
X
NHMC to NO for rural and urban sites, are given in Tables 27 through 30 for August 4,
5, 6, and 7, respectively. Precursor concentrations were generally lower on these days
than on other case study days. With the exception of Camden, NJ (Site 10), urban and
near-urban sites recorded 6:00 to 9:00 a.m. LOT average NO concentrations lower than
0.10 ppm on each of these days. Camden reached an NO concentration of 0.10 ppm on
August 6, but measured lower concentrations on the other days. Franklin Institute
(Site 13) recorded hourly-averaged NO levels in excess of 0.10 ppm later in the morning
X
on August 6 and 7. Much of the NMHC data at the urban and near-urban sites is missing
for these days. The Air Management Service Laboratory (Site 14) was the only urban site
that recorded NMHC on each of these days and the 6:00 to 9:00 a.m. LOT average
concentrations at this site were less than 0.50 on each day. Whereas most sites recorded
low precursor concentrations, it should be noted that Chester, PA, recorded a 6:00 to
9:00 a.m. LOT average NMHC concentration of 2.5 ppm on August 4. Precursor concen-
trations at rural sites were, as usual, low, although on August 4 Lumberton, N3 (Site 3),
experienced 6:00 to 9:00 a.m. LOT NO and NMHC concentrations of 0.03 and 0.3 ppm,
115
-------
Table 26. VERTICAL EXTENT OF THERMAL ROOTS (meters) AS DETERMINED
FROM ACOUSTIC SOUNDER DATA AT SUMMIT BRIDGE, DE (Site 1).
Date
August i+
August 5
August 6
August 7
Time (EST)
0900
0
180
220
280
1000
180
250
300
400
1100
180
270
300
WO
1200
200
270
320
360
1300
250
240
340
280
1400
240
210
290
300
1500
180
200
240
340
1600
100
140
160
300
116
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Table 27. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AiND THE RATIO OF NMHC TO NO FO&
RURAL AND URBAN SITES ON AUGUST t. X
Site
No.
1
2
3
k
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, NJ
Van Hiseville, NJ
6:00 to 9:00 a.m. LOT Averages
N0x
0.01
0.02
0.03
0.02
0.01
NMHC
0.1
0.1
0.3
—
—
NMHC/NO
Ratio
7 . 0: 1
4.3:1
10.0:1
—
—
Urban Sites
6
8
10
12
13
1*
Chester, PA
Northeast Airport, PA
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
—
0.01
0.05
0.07
0.06
0.0*
2.5
—
—
—
—
0.5
—
—
—
—
—
11.8:1
117
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Table 28. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FO&
RURAL AND URBAN SITES ON AUGUST 5.
Site
No.
1
2
3
4
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, NJ
Van Hiseviile, NO
6:00 to 9:00 a.m. LDT Averages
N0x
0.00
0.01
0.03
0.00
0.00
NMHC
0.0
0.1
0.2
—
—
NMHC/NO
Ratio X
—
10.0:1
5.7:1
—
—
Urban Sites
10
12
13
14
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
0.0*
0.03
0.03
0.03
_
—
—
0.3
__
—
—
10.0:1
118
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Table 29. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON AUGUST 6.
Site
No.
1
2
3
14
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, NJ
Van Hiseville, NJ
6:00 to 9:00 a.m. LOT Averages
NOX
0.01
0.01
0.03
0.03
0.01
NMHC
0.0
0.1
0.3
—
—
NMHC/NO
Ratio X
3.0:1
7.0:1
5 . 5: 1
—
—
Urban Sites
10
12
13
1*
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
0.10
0.05
0.06
0.04
—
—
—
0.4
—
—
—
10.0:1
119
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Table 30. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON AUGUST 7.
Site
No.
1
2
3
4
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumber ton, NJ
Robbinsvilie, NJ
Van Hiseviile, NJ
6:00 to 9:00 a.m. LDT Averages
N0x
0.02
0.03
0.04
0.02
0.01
NMHC
—
0.0
0.2
—
—
NMHC/NO
Ratio x
—
1.0:1
4.2:1
—
—
Urban Sites
6
10
12
13
14
Chester, PA
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
_
0.07
0.04
0.06
0.05
0.2
—
0.4
—
0.3
__
—
10.0:1
—
6.6:1
120
-------
respectively. These were almost as high as the concentrations measured at the
near-urban Air Management Service Laboratory (Site 14) on this day.
4.5.4 Ozone Patterns
The areas of peak afternoon ozone on each of the four study days are shown in
Figures 39 through 42. On August 4, high ozone levels (greater than 0.10 ppm) were
recorded at stations to the southeast and northeast of Philadelphia. On August 5, high
levels were measured at Summit Bridge, DE (Site 1), and Ancora, NJ (Site 11), southwest
and southeast of Philadelphia, respectively. On August 6 the high levels were measured at
Lumberton, NJ (Site 3), east of Philadelphia, and Ancora, NJ. On August 7, the highest
concentrations occurred to the east and southwest.
A comparison of the areas of peak concentrations, as shown in Figures 39 through
42, and the resultant wind directions listed earlier in Table 20, show a general pattern of
peak ozone concentrations occurring downwind of Philadelphia, with some interesting
exceptions.
August 4 is a case of peak ozone concentrations not occurring downwind of
Philadelphia. Robbinsville, NJ (Site 4), recorded the highest ozone level in the study area
(0.144 ppm) on August 4 despite its location northeast of Philadelphia. At this site, weak
northerly or northwesterly flow occurred in the morning hours, whereas stronger north-
easterly flow was prevalent by 1500 EST. Other sites in the northeast section of the study
area also reported winds from the northeast in the afternoon, whereas winds at
Downingtown, PA (Site 2), Chester, PA (Site 6), New Brunswick, NJ (Site 16), and Philadel-
phia International Airport (Site 17) reported winds from the northwest. An example of the
afternoon surface wind flow on this day is presented on Figure 43, which shows a
streamline analysis at 1500 EST. This flow pattern set up an area of convergence just
east of Philadelphia. This is supported by National Weather Service observations of
towering cumulus clouds to the southeast of Philadelphia during the afternoon, and by
pibal data which indicate that the winds were northerly or northwesterly over
Wilmington, DE and northerly to northeasterly over Trenton, NJ throughout the afternoon.
The convergent wind flow possibly resulted in a merging of the New York and Philadelphia
plumes just southeast of Philadelphia, which helps explain the ozone pattern indicated in
121
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1*00 EST
1300 E5T
1600 E5T
1700E5T
FIGURE 39. Isopieths of ozone at 1*00, 1500, 1600, and 1700 EST, August 4, 1979.
122
-------
1400 EST
1500 EST
1600 EST
1700 EST
FIGURE ^0. Isopieths of ozone at 1400, 1.500, 1600, and 1700 EST, August 5, 1979.
123
-------
[400 EST
1500 EST
1600 EST
1700 EST
FIGURE 41. Isopleths of ozone at 1400, 1500, 1600, and 1700 EST, August. 6, 1979.
124
-------
1400 EST
1500 EST
1600 EST
1700 EST
FIGURE 42. Isopleths of ozone at 1400, 1300, 1600, and 1700 EST, August 7, 1979.
125
-------
FIGURE 43. Streamline analysis depicting the surface flow across the
study area at 1500 EST on August 1, 1979. The numbers
by the site indicate wind speeds (meters per second).
126
-------
Figure 39. In particular, in light of the observed low morning concentrations in
Philadelphia on this day, it appears that high ozone formed from emission sources in
northern New Jersey was transported across central New Jersey and impacted
Robbinsville, NJ (Site 4), Bristol, PA (Site 7), North Philadelphia Airport (Site 8), and
Lumberton, NJ (Site 3), in the late afternoon. Evidence of ozone transported aloft is
presented later.
Mesoscale surface trajectories constructed for selected air parcels on August 4
confirm the above theory. Air parcels traveled generally north to south and Philadelphia
emissions were advected far to the south. Figure 44 shows trajectories ending at
Robbinsville, NJ (Site 4), and North Philadelphia Airport (Site 8) at times of peak ozone
concentrations (1600 and 1900 EST, respectively). Also shown is a trajectory beginning in
downtown Philadelphia at 0600 EST. The air parcels arriving at Robbinsville, NJ (Site 4),
and North Philadelphia Airport (Site 8) carried ozone concentrations of 0.144 ppm and
0.130 ppm, respectively. They originated near the precursor-rich areas of northern New
Jersey. The air parcel originating in downtown Philadelphia is advected southward into an
area for which no ozone data are available, although Ancora, NJ (Site 11), southeast of
Philadelphia, reported a peak concentration of 0.102 ppm at 1700 EST. Flow reversal at
the end point of this trajectory at about 1700 EST indicates that the Philadelphia plume
did not continue to the south but remained in the study area for possible contribution to
pollutant concentrations on August 5.
The highest ozone concentration recorded on August 5 (0.135 ppm) occurred to the
southeast of Philadelphia at Ancora, NJ (Site 11), at 1300 EST. The surface mesoscale
trajectories shown in Figure 45 show that this site was almost directly downwind of
Philadelphia. However, as was noted earlier, there was no indication of high precursor
concentration in Philadelphia on this day. The 6:00 to 9:00 a.m. LOT average NO
A
concentrations were less than 0.05 at all the urban and near-urban sites that reported this
pollutant on this day (Table 28). Therefore, the high ozone level measured at Ancora may
have resulted from long-range transport or carry-over from the previous day. This idea is
supported by the fact that high ozone concentrations were measured throughout the study
area during the day. Specifically, some high values recorded on this day were 0.119 ppm
at Summit Bridge, DE (Site 1), at 1600 EST; 0.105 ppm at Van Hiseville, NJ (Site 5), at
1100 EST; 0.120 ppm at North Philadelphia Airport (Site 8), at 1600 EST; and 0.100 at
127
-------
FIGURE 44. Surface trajectory for various air parcels located within the study area
on August 4, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 EST; dashed lines are parcels ending at the indicated
site and time. Dots show positions of the parcels at one-hour intervals.
128
-------
Site 11
.135
1300 EST
FIGURE 45. Suriace trajectory for various air parcels located within tne study area on
August 5, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
129
-------
Franklin Institute (Site 13) at 1200, 1*00, and 1800 EST. These sites are located in urban
and non-urban areas which do not appear to be downwind of major source areas. The
surface trajectory for Summit Bridge, DE (Figure 45), indicates source areas for these air
parcels to be primarily rural. Pibal data at Trenton, New Jersey, and Wilmington,
Delaware, indicate that the winds aloft were also primarly westerly or northwesterly
through 2000 m most of the day; however, northerly or northeasterly winds were reported
below 800 m at Trenton prior to 1100 EST. Therefore, ozone transported aloft probably
originated northwest of the study area. The magnitude of ozone levels transported aloft
is discussed below.
On August 6, the ozone patterns and airflow patterns were very similar to those
observed on August 5. The peak ozone concentration of 0.136 ppm was again recorded at
Ancora, NJ (Site 11), again at 1300 EST. The mesoscale trajectories shown in Figure 46
indicate that (as on August 5) Ancora, NJ (Site 11), was directly downwind of Philadelphia.
Ozone concentrations in excess of 0.10 ppm were again recorded at locations not
downwind of Philadelphia (e.g., Sites 1, 3, and 5). The interesting point about the
remarkable similarity between concentration patterns on August 5 and 6 is that August 5
was a Sunday and August 6 a Monday, and the central business district was the apparent
upwind source area on both days. However, there was no indication of high morning
precursors on August 5, whereas on August 6, Camden, New Jersey, measured a 6:00 to
9:00 a.m. LDT average NO concentration of 0.10 ppm.
Ozone patterns on the last day of the four-day episode revealed high ozone
concentrations from the east to southwest of Philadelphia. The southwestern-most
station on August 7, Summit Bridge, DE (Site 1), peaked much earlier than Lumberton, NJ
(Site 3), to the east -- 1300 EST, as compared to 1700 EST. The mesoscale trajectories
shown in Figure 47 help explain this phenomenon. A dramatic flow reversal is indicated at
about 1100 EST. At this time, air parcels carried to the southwest were advected back
toward the northeast. An air parcel originating downtown at 0600 EST was advected to
near Wilmington, and then back up to Claymont, DE (Site 15), by 1500 EST, where a
0.120 ppm ozone was recorded.
The area of origin of the parcel carrying the maximum study area ozone concentra-
tion (0.129 ppm) on August 7, as indicated in Figure 47, is very near to the area of peak
130
-------
FIGURE 46. Surface trajectory for various air parcels located within the study area on
August 6, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at :he
indicated site and time. Dots show the positions of the parcels at one nour
intervals.
131
-------
PHILADELPHI
1500 E5T
FIGURE 47. Surface trajectory for various air parcels located within the study area on
August 7, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
132
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ozone — Lumber-ton, NJ (Site 3). Morning NO and NMHC precursor concentrations at
Lumberton, NJ (Site 3), were 0.04 and 0.2 ppm, respectively (6:00 to 9:00 a.m. EOT
average), ievels not usually associated with high ozone concentrations.
1.5.5 NO_2 Patterns
Peak NC>2 concentrations for the four days (August 4 through 7) ranged from 0.070
to 0.090 ppm. These peak concentrations occurred in Philadelphia, with the exception of
August 6, when the peak NO2 concentration occurred east of Philadelphia at
Lumberton, NJ (Site 3). The NG>2 peak of 0.074 ppm at Site 3 occurred at the unusual
time of 0200 EST. Sites to the west (Philadelphia) and to the northeast (Robbinsviile, NJ,
Site 4) of Site 3 also reported elevated levels at this time. Ail the peak concentrations
occurring in Philadelphia on August 4, 5, and 7 were reported in the late evening or early
morning hours, reflecting the decomposition of ozone into NCU and oxygen. Daytime NG>2
levels were generally much lower, with rural stations reporting less than 0.01 ppm.
4.5.6 Concentrations Aloft
Direct measurement of concentrations aloft by the helicopter was made on all four
study days. Average ozone concentrations aloft were determined from helicopter
soundings at upwind sites and are summarized in Table 31. No early morning soundings
were made on August 4 or 5.
Transport aloft on August 4 appears to be about average when compared to other
case study days. Average ozone concentrations of 0.05 to 0.06 ppm were observed in late
morning soundings made over West Chester, PA, to the west of Philadelphia, over
Philadelphia, and over Medford, NJ, to the east of Philadelphia. Moreover, concentrations
aloft recorded during transects between West Chester, PA, downtown Philadelphia, and
Medford, NJ, on this flight were between 0.03 and 0.06 ppm. Surface stations reported
similar levels at 1000 EST, the first hour of uninhibited vertical mixing. Concentrations
aloft obtained during the mid-afternoon helicopter flight present some interesting data.
Evidence was presented earlier in discussing ozone patterns, which indicated that the high
ozone levels recorded at the surface to the northeast, east, and southeast of Philadelphia
in part resulted from ozone transported from northern New Jersey and New York City.
133
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Table 31. AVERAGE MIXED LAYER OZONE CONCENTRATIONS ALOFT ON
AUGUST *, 5, 6, AND 7, 1979 (morning concentrations reflect
levels from the top of that afternoon's mixing layer to the
top of the layer of ozone depletion).
Date
August *
August 5
August 6
August 7
Time
(EST)
0936
1012
1052
1328
1*10
1*52
0758
0833
0907
0555
0631
0702
0919
09*8
1028
1*18
0557
0628
0656
0855
0925
1020
1328
1*07
1*37
Approximate
Location
West Chester, PA
Downtown
Medford, NO
Downtown
Robbinsville, NJ
15 km SE of
Medford, NO
West Chester, PA
Downtown
Medford, NJ
Pipersville, PA
Pottstown, PA
Downtown
Willow Grove, PA
Downtown
Seabrook, NO
Hammonton, NJ
Pipersville, PA
Pottstown, PA
Downtown
Willow Grove, PA
Downtown
Seabrook, NJ
Downtown
Hammonton, NJ
Seabrook, NJ
Position with
Respect to
Philadelphia
Under
Prevailing
Flow
Crosswind
—
Crosswind
Crosswind
Crosswind
Crosswind
—
Downwind
Upwind
Upwind
—
Upwind
—
Downwind
Downwind
Crosswind
Crosswind
—
Upwind
—
Crosswind
—
Crosswind
Crosswind
Ozone
(ppm)
0.060
0.050
0.060
0.060
0.070
0.110
0.050
0.055
0.060
0.030
0.030
0.025
0.035
0.0*0
0.060
0.090
0.015
0.020
0.015
0.020
0.025
0.020
0.050
0.050
0.060
13*
-------
Figure 48 shows ozone concentrations recorded by the helicopter during
mid-afternoon transects from (a) downtown Philadelphia to Robbinsville, NJ; (b) from
Robbinsville, NJ, to the site 15 km southeast of Medford, NJ (Site G in Figure 6); and (c)
from Site G to Wilmington, DE, where the helicopter landed. Moderate ozone levels,
between 0.05 and 0.08 ppm were recorded between Philadelphia and Robbinsville and
similar levels were recorded during a sounding made over Robbinsville. As the helicopter
transected to the southeast portion of the study area, from Robbinsville to Site G, at an
approximate altitude of 350 m MSL, higher ozone levels, between 0.08 and 0.12 ppm, were
seen; the sounding made over Site G revealed ozone levels above 0.13 ppm at bout 700 m
MSL. As the helicopter flew from Site G to Wilmington, DE, ozone levels were more
variable than during the two previous transects, fluctuating between 0.08 and 0.15 ppm.
As noted earlier, a zone of convergence characterized by towering cumulus existed
earlier, southeast of Philadelphia at this time, which helps explain the variation.
Indications of transport aloft on August 5 are ambiguous. A mid-morning vertical
sounding over West Chester, PA, is shown in Figure 49. It shows an average concentration
in the mixed layer of 0.05 ppm, which is not particularly high. An inversion based just
below 500 m is also apparent with generally light northerly winds at all levels. The
ground- level concentration at nearby Downingtown, PA (Site 2), during the first hour of
uninhibited vertical mixing (as determined from the Site 1 acoustic sounder) was
0.058 ppm, corresponding fairly well to the ozone levels aloft shown in Figure 49.
However, ground-level ozone concentrations at Summit Bridge, DE (Site 1), and
Van Hiseville, NJ (Site 5), during the first hour of uninhibited vertical mixing (as deter-
mined from the Site 1 acoustic sounder) were 0.084 and 0.104 ppm, respectively. Both
these levels were among the highest 1000 EST concentrations observed at these sites and
imply high levels of ozone transported aloft. While no helicopter data are available for
near these sites in the morning on this day, the helicopter did record occasional values in
excess of 0.150 ppm while transecting from Philadelphia to Medford, NJ, at about
1000 EST, as shown in Figure 50. Thus, morning ozone levels aloft were not homogeneous
across the study area and pockets of elevated ozone aloft were apparent. This
inhomogeneity may have been the result of the previous day's convergent wind flow as
discussed earlier.
Measurements aloft in the afternoon indicate ozone levels of about 0.08 ppm over
central New Jersey, increasing sharply to the southeast and south of Philadelphia. Very
135
-------
a.
a.
(a)
Ozone Concentration
o o o o
• • « •
0 0 O >—
O .p- OO NJ
Altitude —690 m MSL
11,1
1348 1350 1352 1354
Philadelphia, PA Time
1356
(EST)
'
\ \
1358 1400
Robbinsville, NJ
Ozone Concentration (ppm
0 0 O 0
O 0 0 I—
O 4^ 00 K)
(b)
^ -^^
Altitude —350 m MSL
i i i i i iii
1422 1424 1426 1428 1430 1432 1434 1436
Robbinsville, NJ Time (EST") Medford, NJ
(c)
CL
Q.
70.12
o
20.08
^0.04
o
U
-------
O-
NO
-4
in
1_
-------
0.24
e o.2o
g 0.16
*j
re)
c 0.12
0)
u
O 0.08
o
O
0.00
0950 0952
Philadelphia, PA
0954
0956
Time (EST)
0958
1000 1002
Medford, N3
FIGURE 50. Ozone concentrations reported during helicopter transect
from downtown Philadelphia to Medford, N3 on August 5,
1979 at an altitude of approximately 550 m MSL.
-------
high concentrations (in excess of 0.200 ppm) were measured aloft during a transect from a
location 15 km southeast of Medford, NJ, to Wilmington, DE, at about 1500 EST.
On August 6, indications of transport aloft from surface measurements are quite
different from helicopter soundings. Many sites recorded elevated ozone levels during the
first full hour of uninhibited vertical mixing, as determined by the acoustic sounder. At
1000 EST, the ozone levels were 0.080 ppm at Summit Bridge, DE (Site 1), 0.065 ppm at
Lumberton, NJ (Site 3), 0.076 ppm at Robbinsville, NJ (Site 4), and 0.074 ppm at
Van Hiseville, NJ (Site 5). These were ail well-above average 1000 EST ozone concentra-
tions and indicate significant ozone levels aloft. Considering that the flow direction on
August 5 was from the northwest (see Figure 45), it is posible that a reservoir of elevated
ozone was left aloft to the east and southeast of Philadelphia from the previous day.
However, early morning helicopter soundings indicate much lower average ozone
concentrations (about 0.03 ppm) aloft in the northwestern portion of the study area (see
Table 31). Transects made during the morning flights also indicate low ozone
concentrations aloft — less than 0.05 ppm. Similar levels were measured at sites to the
northwest of Philadelphia at 1000 EST; 0.035 ppm at Ailentown, PA; 0.038 ppm at
Lancaster, PA; 0.026 ppm at Reading, PA; 0.046 ppm at Morristown, PA; and 0.021 ppm at
Bethlehem, PA (these sites record ozone concentrations but did not participate in the
study). An afternoon transect made at approximately 430 m MSL between
Hammonton, NJ, and Seabrook, NJ, southeast of Philadelphia (see Figure 6), at about
1430 EST indicated ozone concentrations in excess of 0.10 ppm and a sounding over
Hammonton, NJ, showed an average ozone level in the mixed layer of 0.09 ppm.
Ancora, NJ (Site 11), reported a surface concentration of 0.119 at this time.
Transport of ozone aloft on August 7 was apparently minimal. As on August 6, the
early morning helicopter soundings show very low ozone levels aloft (Figure 51). This
figure shows vertical profiles of ozone, NO , and temperature over Pottstown, PA, along
A
with the vertical wind profile obtained at Robbinsville, NJ (Site 4). The wind profile is
interesting, considering the dramatic flow reversal from northeast to southwest experi-
enced at the surface later in the day. Average ozone levels observed aloft during ail
morning soundings were less than 0.025 ppm. Furthermore, ozone concentrations
measured by the helicopter while transecting between sites were less than 0.06 ppm
during the morning and mid-morning flights, and less than 0.08 ppm during afternoon
139
-------
o.
NO
Temperature
2500
2000
(7J1500
s
10
-
15(
^
10
>
>
?
>- 5(
3
i i i i i
0 0.04 0.08 0.12
Concentration (ppm)
0 0.02 0.04 0.06 0.08
Concentration (ppm)
i 0
I
\
10
15 20 25 30
Temperature ( C)
FIGURE 51. Vertical profiles of O,, NO , and Temperature obtained by the instrumented helicopter
over Pottstown, PA (bite J^ at 0628 EST on August 7, 1979. Also shown is the corresponding
wind profile. (Key: f = North at 5 m/s)
-------
flights after uninhibited mixing had occurred. Thus, little ozone was available aloft to
supplement local production. Ozone levels observed at the surface on this day confirm
the helicopter observations. The first hour of uninhibited vertical mixing was 1000 EST.
Surface ozone levels observed at this time were 0.047 ppm at Summit Bridge, DE (Site 1),
0.031 ppm at Downingtown, PA (Site 2), and 0.042 ppm at Lumberton, NJ (Site 3), all
much lower than the levels observed on the previous two days.
4.5.7 Hydrocarbon Species Data
Although August 4 was a Saturday, the early morning hydrocarbon levels at the
Franklin Institute site were higher (but only slightly) than average and also higher than the
industrial site samples. Again, some departures from average speciation were seen. Both
samples at Franklin Institute were quite high in aromatics, especially Cg-C,Q. In the
0700 to 0800 EST sample, this was balanced by high levels of C.-Cc paraffins, probably
from a local source of gasoline vapor. In the early Franklin Institute sample, the
iso-butane exceeded n-butane, which is unusual. In most samples, n-butane exceeds
iso-butane, but n-butane is smaller than iso-pentane. But gasoline brands do differ in the
distribution among those four species. The two industrial site samples were nearly
average with only a slight increase in C^ olefins, especially in the 0700 to 0800 EST
sample.
Also on August 4, a sample taken at Flat Rock Park at the outskirts of Philadelphia
at noon showed 222 ppbC of NMHC. This sample was quite near the overall sample
average. The propene/acetylene ratio was 0.33; very near the automobile exhaust value
and that for unreacted air. Most samples in this program were appreciably higher in
propene than this.
Helicopter samples were also taken in the late morning of August 4 over the river
near downtown. The two samples taken were similar in composition and quite normal,
except for the 450-m altitude sample which showed 17.5 ppbC of iso-propylbenzene
(cumene). As mentioned earlier, this is an important industrial hydrocarbon, and sporadic
high concentrations may reflect chance sampling of a point source. The propene/acety-
lene ratios were again near those of gasoline engine exhaust.
141
-------
A sample taken at 1255 EST in northwest Philadelphia on August 4 had an NMHC
concentration of only 119 ppbC. Only 15 hydrocarbons were measurable, but these were
compounds normally present in the largest concentrations.
Although peak ozone values of 0.135 ppm occurred on August 5, both Franklin
Institute and industrial site samples had quite low NMHC in all four early morning
samples. The type distributions were very close to the average. The species distribution
was also very close to average. Since it was a Sunday, perhaps the composition of the air
mass was not significantly affected by the emissions associated with low traffic density.
Two helicopter samples were taken on this Sunday over the Delaware River near
downtown at about 0845 EST. The sample at 457 m had only 10 measurable hydrocarbons,
totaling 59 ppbC. The type distribution appears abnormal because only one aromatic and
no olefins (except ethylene, which is not credible) were measurable. The very low NMHC
suggests that this sample was taken above the inversion. The mixing height was just over
147 m at this time. At 24 m altitude, the total NMHC was 447 ppbC, with a normal
distribution. The iso-propylbenzene was only 1 ppbC compared to 17.5 ppbC on the
previous day (August 4). A sample taken in Downingtown, PA at 0600 EST on August 5
yielded 149 ppbC with no abnormalities. This total is substantially lower than at the other
sites probably because of its distance from heavy traffic areas.
The airflow on August 6 when the ozone reached 0.136 ppm was from the northwest.
The mixing heights in late morning were about 600 meters. At Franklin Institute and
industrial sites, NMHC was near or below average and the type distributions were within
the normal range. All but the 0600 to 0700 EST Franklin Institute samples showed slightly
elevated C,-C. olefins.
Helicopter samples taken at 1000 EST near downtown at 488 m and at 18 m MSL
were quite similar. In this case, the upper sample was taken just below the mixing height,
which was 591 m. The species and type distributions showed no recognizable abnormali-
ties. Iso-propylbenzene was not measurable (or at least not reported).
At 0600 EST samples were taken above Pipersville, PA (a rural area 52 km north of
Philadelphia) at 457 m MSL. Only seven hydrocarbons were measured totaling 23 ppbC.
142
-------
Near the surface about 127 ppbC were found. The unusual feature of this analysis is that
methyl styrene was the only olefin reported except for 34 ppbC of ethyiene. This is surely
an artifact, since the higher elevation sample showed the same concentration. Acetylene
was also not reported, otherwise this could be light automobile exhaust.
A sample taken at an unspecified time in northwest Philadelphia had only 102 ppbC
of NMHC in a normal species distribution.
Winds on August 7 were light but the mixing heights were fairly high. The NMHC at
0500 to 0600 EST at the industrial site was, therefore, only 272 ppbC and only 369 at 0700
to 0800 EST. The early sample at Franklin Institute is missing but the 0700 to 0800 EST
sample was fairly high (949 ppbC). A somewhat elevated level of higher aromatics (C > S)
may indicate an intrusion of a solvent. Otherwise, these three samples are quite normal.
An early afternoon sample taken at Flat Rock Park in northwest Philadelphia was quite
low (NMHC = 108 ppbC). The paraffin percentage is high probably because many
aromatics were too small to measure, but the butanes and pentanes were readily
measurable. Four helicopter samples were taken on this day. The two taken over
Pipersville, PA far north of Philadelphia showed only 37 ppbC (at 0606 EST and 457 m
MSL, and 26 ppbC at 0608 EST and 46 m MSL). The compounds detected are just those
usually present in largest concentration. The other two helicopter samples were taken
near downtown during mid-morning and had concentrations comparable to the Franklin
Institute and industrial site samples (305 ppbC at 457 m MSL at 0936 EST, and 230 ppbC
at 46 m MSL at 0939 EST). The distributions were normal, but it may be noteworthy that
the higher altitude gave the higher concentrations.
143
-------
4.6 AUGUST 10, 1979 (FRIDAY)
The interesting features of the August 10 case were (1) the implication of source
areas to the southwest, (2) the advection of the central business district's emissions out of
the study area under the influence of strong winds, and (3) the prefrontal nature of the
high ozone levels.
The peak ozone concentration recorded on August 10 was 0.170 ppm. Seven of the
fifteen operating stations recorded ozone concentrations in excess of 0.12 ppm and an
additional five reported levels equal to or greater than 0.10 ppm. The peak NG>2 concen-
tration was 0.080 ppm with five stations reporting NCu concentrations > 0,05 ppm.
4.6.1 Synoptic Meteorology
The synoptic situation is shown in Figure 52. The study area was positioned in the
warm sector of a frontal system after a warm frontal passage on the previous day. The
Bermuda high-pressure cell, centered just off the Georgia coast, exerted some influence
and, together with a low pressure center moving north of the Great Lakes, brought south-
westerly flow to the study area. Afternoon and evening thundershowers occurred over the
area, and the cold front associated with this cyclone passed through Philadelphia the
following morning (August 11) cleansing out the study area. Thus, the high ozone levels of
August 10 were associated with prefrontal conditions.
Synoptic trajectories terminating at Philadelphia on August 10 are shown in
Figure 53. A long, over-land trajectory is evident. Due to high wind speeds, the air
parcel in the 100- to 500-m layer passed over the Washington, D.C.-Baltimore area less
than 12 hours prior to its arrival in Philadelphia.
4.6.2 Mesoscale Meteorology
Winds at all levels exhibited the highest speeds of any case study day. Resultant
wind speeds were generally > 2.5 m/s at the surface all day, while winds aloft were
generally about 8.0 m/s, as compared to 2 to 4 m/s on other case study days. Surface
flows were southwesterly in the morning hours with significant horizontal shear in the
-------
I A 1016
1012
• MONTRE1L
FIGURE 52. Synoptic situation, 0700 EST, August 10, 1979.
-------
45 °j
FIGURE 53. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 10, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
-------
afternoon. Winds were southwesterly in the southwestern portion of the study area with
stations elsewhere reporting northwesterly, all with high speeds. Winds aloft were more
consistent from the west across the study area.
Late morning urban mixing heights were lower compared with other case study days,
although afternoon mixing heights were relatively high. The 0900 EST mixing height (as
determined by radiosonde observations) was 339 m, as compared to 1516 m at 1500 EST.
Based upon surface temperatures between 0900 and 1500 EST and the 0900 sounding,
mixing heights did not rise above 503 m MSL until 1300 EST and reached a maximum value
of 1516m MSL at 1400 EST. Rural mixing height, as derived from acoustic sounder data,
did not break the 1000-m level until 1100 EST, the latest of any case study day. Vertical
mixing was fair when compared to other case study days, while horizontal mixing was very
vigorous due to high wind speeds.
4.6.3 Precursor Patterns
The 6:00 to 9:00 a.m. LOT averages of NO and NMHC, along with the ratio of
NMHC to NO , are given in Table 32 for rural and urban sites. Morning downtown NMHC
X
levels were substantial, as reflected in the 1.0 ppm 6:00 to 9:00 a.m. LOT average at
South Broad Street (Site 12). The corresponding NOx average was 0.050 ppm. Other
urban sites were above average when compared to other case study days, despite the fact
that ventilation was excellent due to the high wind speeds.
4.6.4 Ozone Patterns
Isopieths of ozone concentrations at 1300, 1400, 1500, and 1600 EST are shown in
Figure 54. High concentrations (greater than 0.10 ppm) were recorded at sites east to the
northeast, southeast, and southwest of Philadelphia during the afternoon. At 1500 EST,
Claymont, DE (Site 15), reported the highest ozone concentration in the study area that
day. It is interesting to note that, with strong flow from the southwest, the peak
concentrations occurred southwest of Philadelphia, suggesting that emissions from
Philadelphia were not contributing to those peaks.
Further evidence implicating a source area other than Philadelphia is seen in
Figure 55. Air parcels tracked backward from Claymont, DE (Site 15), at 1500 EST (time
147
-------
Table 32. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FOR
RURAL AND URBAN SITES ON AUGUST 10.
Site
No.
1
2
3
*
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, NJ
Van Hiseville, NJ
6:00 to 9:00 a.m. LOT Averages
N0x
0.00
0.01
0.01
0.02
0.00
NMHC
0.2
0.0
0.0
—
—
NMHC/NO
Ratio X
0.0:1
—
—
—
—
Urban Sites
6
10
12
13
1*
Chester, PA
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AM5 Lab, Philadelphia, PA
—
0.04
0.05
0.07
0.08
0.3
—
0.1
—
0.6
__
—
19.4:1
—
7.5:1
-------
1300 EST
1^00 EST
1300 EST
1600 EST
FIGURE 54. Isopieths of ozone at 1300, 1400, 1500, and 1600 EST, August 10, 1979.
1U9
-------
100C
FIGURE 55- Surface trajectory for various air parcels located within the study area on
August 10, 1979. Solid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
150
-------
of peak ozone) and forward from the central business district at 0600 EST indicate a
source region far to the southwest and that emissions from the central business district
are advected out of the study by 1400 EST. The urban centers of Baltimore and
Washington, D.C., are upwind of the study area on this day. The high wind speeds
provided the necessary mechanism for the rapid transport of the emissions from these
urban centers into the study area in less than ten hours.
4.6.5 NQ2 Patterns
The peak NC>2 concentration (0.080 ppm) was observed at the A MS Lab (Site 14),
during the late morning hours. South Broad Street, PA (Site 12), another urban site, also
peaked during late morning. Such late morning peaks are probably the result of the
reaction of high levels of early morning NO with ozone and occur before NO_ destruction
by sunlight and reactions with hydrocarbons. NO2 levels were quite low at outlying sites
with the exception of Robbinsville, NJ (Site 4), which reported elevated concentrations
(0.067 ppm) in the evening (2000 EST) reflecting the scavenging of the day's ozone.
4.6.6 Concentrations Aloft
Early morning helicopter soundings show evidence of ozone transport aloft of
0.06 ppm in the 500- to 2000-m layer. The sounding made near the area's southwestern-
most site, Summit Bridge, DE (Site 1), is shown in Figure 56. Peak ozone levels were
found at approximately 900 m MSL where the wind was from the west-southwest at
9.1 m/s. Virtually no NO was detected aloft, while an inversion based near the surface is
evident. Ozone concentrations measured by the helicopter while transecting from West
Chester, PA, to Philadelphia at about 0630 EST varied between 0.06 and 0.09 ppm. The
mid-morning helicopter flight showed higher ozone levels. Concentrations between 0.09
and 0.12 ppm were measured by the helicopter during a transect between Brandywine, PA
(about 8 km southeast of West Chester, PA), and Philadelphia at about 0916 EST, as shown
in Figure 57.
Another indication of transport aloft is that Summit Bridge, DE (Site 1) and
Downingtown, PA (Site 2) reported 0.079 and 0.087 ppm, respectively, during the first
hour of uninhibited vertical mixing (1100 EST). Diurnal profiles of ozone concentrations
151
-------
NO.
Temperature
LO
0)
5
2000
1500
1000
500
2500
2000
1500
1000
500
2500
2000
1000
500
i i
0 0.04 0.08 0.12 0 0.02 0.04 0.06 0.08
Concentration (ppm)
Concentration (ppm)
10 15 20 25 30
Temperature ( C)
FIGURE 56. Vertical profiles of O., NO , and Temperature obtained by the instrumented helicopter
over Summit Bridge, DE (stfeA) at 0535 EST on August 10, 1979. Also shown is the corresponding
wind profile. (Key: )• - North at 5 m/s)
-------
a.
^x
o
*j
n)
u
£
§
o
O
ID
o
0.20
0.16
0.08
0.04
0.00
09U
Ikandywine, PA
0916
Time (EST)
0918
0920
Philadelphia, PA
FIGURE 57. Ozone concentrations reported during helicopter transect from Brandy wine, PA to Philadelphia
on August 10, 1979 at an altitude of approximately 850 rn MSL.
-------
at these sites are given in Figure 58. Ozone peaks eariy in the day are apparent at both
sites. Both sites exhibit similar ozone levels at the time of initial mixing from aloft.
However, Summit Bridge concentrations continue to increase in response to transport
from the southwest, but Downingtown levels do not, suggesting that little of this transport
affects the western portion of the study area.
4.6.7 Hydrocarbon Species
At Franklin Institute, the hydrocarbon species type distribution showed high
paraffins, mostly propane and butanes. The C., to C^ olefins were slightly elevated as
well. It is not clear what these should be ascribed to.
In contrast, the 0500 to 0600 EST sample at the industrial site showed a large
percentage of aromatics; most of this was benzene (185 ppbC). This must be attributed to
a local source but it was transitory since the 0700 to 0800 EST sample was nearly normal
in distribution (20.3 ppbC benzene). Surprisingly, both samples showed six carbon olefins
(1-hexene and C-2-hexene) although in this case the later sample was higher in
concentration. It is difficult to explain this since we lack signatures for possible sources.
To maintain perspective it must be kept in mind that these "intruders" were in no case a
major part of the NMHC.
West Chester is a small city about 25 miles west of Philadelphia. A sample taken at
an unspecified time on August 10 showed a high total NMHC of 907 ppbC. This was
heavily weighted with light paraffins. The butanes and pentanes made up about 4396 of
this total. This is probably a case of gasoline vapor since minimal concentrations of
higher aromatics were measured and is probably due to a local source.
An afternoon sample was taken at 1300 to 1400 EST at the industrial site. The
distribution was normal with a total NMHC of 390 ppbC. It is surprising that the two
aromatic olefins — styrene and methyl styrene -- were the only olefins, except for
propene, reported in this sample.
At 0621 EST on this date, a sample was taken at 488 m MSL near West Chester,
Pennsylvania. Only 99 ppbC was reported in a normal pattern although neither ethylene
154
-------
0.18
Summit Bridge, DE
/ (Site 1)
0300
0700
1100 L500
Time (E5T)
1900
2300
FIGURE 58. Diurnal profiles of ozone at Summit Bridge, DE (Site 1) and
Downingtown, PA (Site 2) on August 10, 1979.
155
-------
nor acetylene was listed. At about 0940 EST, samples were taken over downtown at two
altitudes. These were similar in composition, the upper sample taken just below the
mixing height of 339 m, showing 875 ppbC NMHC at 488 m MSL, and the lower sample
showing 702 ppbC at 18 m MSL. Both showed high percentages of paraffin due to high
propane concentrations. Propene levels were also slightly elevated.
156
-------
4.7 AUGUST 22, 1979 (WEDNESDAY)
Some of the interesting features of this day were: (1) high ozone leveis in
Philadelphia proper, as well as downwind, (2) the evidence of significant wind shear aloft,
and (3) a low-level synoptic trajectory with a long residence time over the Northeast
Corridor.
The maximum ozone and NO2 concentrations reported on August 22 were 0.140 and
0.100 ppm, respectively. Four of the fourteen operating stations reported ozone concen-
trations equal to or greater than 0.12 ppm and one other station reported 0.100 ppm.
Seven sites reported NCX concentrations > 0.05 ppm.
4.7.1 Synoptic Meteorology
The synoptic situation on this day is illustrated in Figure 59. Although, like
August 10, the wind flow was predominantly from the southwest, the synoptic situation
was quite different. A low-pressure center had passed through the study area from the
northwest on August 21 with precipitation in the study area on August 20 and 21. On
August 22, a high-pressure ceil was rebuilding over the area. The center of this high
pressure was over southern Quebec at 0700 EST on August 22, moving offshore toward the
southeast.
The synoptic trajectory for an air parcel in the 100- to 500-m layer, shown in
Figure 60, is somewhat puzzling. While surface flow over the study area was consistently
from the southwest and, as will be shown later, surface study area trajectories confirmed
this southwesterly flow, the trajectory of an air parcel in the 100- to 500-m layer
approached from the northeast during the 12 hours preceding 1300 EST. Winds aloft data
show wind shear but only at very high levels (i.e., 1500 m MSL). Prior to the erratic
behavior and long residence time in the vicinity of major Northeast Corridor urban
centers, the synoptic trajectory shown in Figure 46 exhibits a long, over-land, anti-
cyclonic approach to Philadelphia. A trajectory for a parcel in the 1500- to 2000-m layer
approached more directly from north-northwest.
157
-------
00
40°
75'
FIGURE 59- Synoptic situation, 0700 EST, August 22, 1979,
-------
45'
FIGURE 60. Synoptic trajectory of air parcels arriving at Philadelphia at 1300 EST, August 22, 1979. Solid line indicates
parcel in the 500 to 1000-meter layer; dashed line is for a parcel in the 1500 to 2000-meter layer. Intervals
are six hours.
-------
4.7.2 Mesoscale Meteorology
The prevailing surface wind flow was generally southwesterly all day, although some
variability was noted during the late morning hours, particularly at Sites 7, 8, and 21.
These sites showed some tendency toward northerly winds, although the prevailing
directions for the day were south to southwest. Winds aloft were northwesterly in the
early morning backing to southwesterly by 1500 EST with northeast winds at 1500 m MSL.
Urban mixing heights were generally higher than on other case study days. The
maximum afternoon mixing height was 1707 m MSL at 1500 EST. Rural acoustic sounder
data indicate mixing through the 1000 m MSL layer by 0915 EST, with excellent vertical
mixing throughout the day.
4.7.3- Precursor Patterns
The 6:00 to 9:00 a.m. LOT averages of NMHC and NO. along with the ratio of
J\
NMHC to NO , are given in Table 33 for rural and urban sites. Morning precursor levels
X
were above average throughout the study area. The 6:00 to 9:00 a.m. LDT NO
concentrations at ail sites near the central business district were above 0.05 ppm; even
Robbinsville, NJ (Site 4), experienced NO concentrations three times the normal
average. NMHC levels were also somewhat elevated with South Broad Street (Site 12),
and the AMS Lab (Site 14) reporting 6:00 to 9:00 a.m. LDT levels of 1.1 and 0.7 ppm,
respectively, resulting in 6:00 to 9:00 a.m. LDT NMHC/NOx ratios of 12.2:1 and 5.4:1,
respectively. Summit Bridge, DE (Site 1), Downingtown, PA (Site 2), and Lumberton, N3
(Site 3), reported higher-than-normal NMHC concentrations — 6:00 to 9:00 a.m. LDT
averages of 0.4, 0.3, and 0.3 ppm, respectively.
4.7.4 Ozone Patterns
Peak study area ozone levels were observed at stations in Philadelphia and to the
east and northeast. The AMS Lab in Philadelphia (Site 14) recorded the highest ozone
concentration of the day with 0.140 ppm at 1400 EST. Figure 61 shows ozone patterns
over the study area at 1400 and 1500 EST. Unfortunately, an area-wide investigation of
afternoon ozone concentrations in the study area is plagued by missing afternoon data at
160
-------
Table 33. 6:00 to 9:00 a.m. LOT (0500-0800 EST) AVERAGES OF NO
and NMHC (ppm) AND THE RATIO OF NMHC TO NO FO&
RURAL AND URBAN SITES ON AUGUST 22. X
Site
No.
1
2
3
*
5
Rural Sites
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Robbinsville, Nd
Van Hiseville, Nd
6:00 to 9:00 a.m. LDT Averages
NO
X
0.02
0.02
0.0*
0.09
0.01
NMHC
0.*
0.3
0.3
—
—
NMHC/NO
Ratio X
20:0.1
13.5:1
7.5:1
—
—
Urban Sites
8
10
12
13
1*
Northeast Airport,
Philadelphia, PA
Camden, NJ
So. Broad & Spruce Streets,
Philadelphia, PA
Franklin Institute,
Philadelphia, PA
AMS Lab, Philadelphia, PA
0.07
0.15
0.09
0.06
0.13
—
—
1.1
—
0.7
—
—
12.2:1
—
5.^:1
161
-------
EST
1500 E5T
FIGURE 61. Isopieths of ozone at 1*00 and 1.500 EST, August 22, 1979.
162
-------
most northeasterly stations. Concentrations upwind (to the southwest) are low. None of
the stations to the southwest, west, or southeast of Philadelphia reported ozone levels in
excess of 0.10 ppm at any time during the day.
Mesoscale surface trajectories for two air parcels of interest are shown in
Figure 62. An air parcel arriving at the AMS Lab, Philadelphia (Site 14), at 1400 EST with
0.140 ppm of ozone passed through Philadelphia the previous hour and over precursor
source areas along the Delaware River earlier in the morning. The 0600 EST emissions
from Philadelphia's central business district were advected slowly to the northeast and
were in the vicinity of Bristol, PA (Site 7), by about 1400 EST. Unfortunately, no ozone
data for that site is available past 1200 EST when a concentration of 0.099 ppm was
recorded. Nearby, North Philadelphia Airport (Site 8) reported 0.130 ppm of ozone at
1400 EST. The mesoscale trajectories show that surface advection was similar in
direction to August 10 but wind speeds were much lower. Still, source areas other than
Philadelphia, but within the study area, are again suggested as the explanation of high
ozone levels.
4.7.5 NO2 Patterns
The highest NO^ concentrations of the day occurred in Philadelphia and Camden, NJ
(Site 10), in the early afternoon (e.g., 0.10 ppm at South Broad Street (Site 12) at
1300 EST) due to the availability of both NO and ozone for NO-, production. The peak
concentration of 0.095 ppm at Camden, NJ (Site 10), occurred at 0700 EST and corres-
ponded to a drop in NO concentration from 0.179 ppm (the highest level of the day) to
0.062 ppm and preceded a large increase in ozone levels. Other concentrations in excess
of 0.05 ppm occurred in the morning at outlying sites.
4.7.6 Concentrations Aloft
Although vertical pollutant profiles aloft are lacking, some indication of early
morning ozone and precursor transport aloft can once again be found by a review of
surface concentrations during the first complete hour of uninhibited vertical mixing
which, according to the acoustic sounder at Summit Bridge, DE (Site 1), was 1000 EST.
The diurnal profile of ozone at Summit Bridge, DE, and Downingtown, PA, is shown in
163
-------
FIGURE 6Z. Surface trajectory for various air parcels located within the study area on
August 22, i979. Soiid line indicates a trajectory beginning at downtown
Philadelphia at 0600 E5T; dashed lines are for parcels ending at the
indicated site and time. Dots show the positions of the parcels at one hour
intervals.
-------
Figure 63. The rapid increase in ozone levels characteristic of ozone mixing down from
aloft can be seen, especially at Summit Bridge. Concentrations (ppm) at these sites at
1000 EST were:
Location
Summit Bridge, DE (Site 1)
Downingtown, PA (Site 2)
Ozone
0.077
0.062
NO
0.000
0.000
NMHC
0.50
0.10
These data indicate substantial levels of ozone aloft. The 0.077 ppm ozone level
observed at Summit Bridge, DE (Site 1), at 1000 EST was the maximum for the day.
Although substantial NMHC is present (0.50 ppm, an unusually high level for 1000 EST),
indicating at least some of the raw material of further ozone production is available, NO
and NO are lacking. The apparently substantial levels of transported ozone and low
maximum concentrations upwind of Philadelphia are puzzling. Unfortunately, no actual
measurements of ozone aloft are available.
165
-------
0.1*
0.12
~ 0.10
o
•M
0.08,
u
0.06
c
o
O 0.04
0.02
0.00
Downingtown, PA
j (Site 2)
Summit Bridge, DE
(Site 1) \
\
0300
0700
1100
Time (EST)
1900
2300
FIGURE 63. Diurnal profiles of ozone at Downingtown, PA (Site 2) and
Summit Bridge, DE (Site 1) on August 22, 1979.
166
-------
5. CONCLUSIONS
The analysis of the ten case study days discussed in the previous chapter has led to
the following findings:
Ozone levels aloft in the early morning on days of high surface ozone vary
from 0.015 to 0.097 ppm.
Significant nighttime ozone transport aloft can be a major cause of high late-
afternoon surface ozone concentrations in urban and rural areas.
Peak ozone levels do not always occur in the Philadelphia urban plume.
The ozone transport phenomenon in the Northeast Corridor involves local,
mesoscale, and synoptic scale transport.
5.1 MORNING OZONE LEVELS ALOFT
During the ten case study days, early morning ozone levels observed aloft were as
low as 0.015 ppm and as high as 0.097 ppm. Table 34 summarizes the ozone concentra-
tions aloft observed generally upwind of Philadelphia for the case study days. Two
methods were used to estimate these concentrations aloft: (1) the actual average
concentration measured aloft by helicopter above the layer of surface ozone depletion and
below the top of the afternoon mixed layer; and (2) the average concentration observed at
the surface during the first full hour of complete vertical mixing through the 1000-m
layer, as determined by the acoustic sounder located at Summit, DE (Site 1). An assumed
complete vertical mixing time of 1000 EST, based upon the average time of complete
mixing on other case study days, was used for 3uly 12, 13, and 16, due to the unavailability
of acoustic sounder data. Average concentrations detected aloft ranged from 0.015 to
0.020 ppm on August 7 to 0.060 ppm on August 10. Ozone concentrations measured at the
surface at the time of complete vertical mixing ranged from 0.031 to 0.047 ppm on
August 7 to concentrations in excess of 0.080 ppm on July 13, 19, and August 10.
167
-------
Table 34. SUMMARY OF MORNING OZONE CONCENTRATIONS (in ppm) OBSERVED GENERALLY UPWIND
ON CASE STUDY DAYS.
Date
July 12
July 13
July 16
July 19
August 4
August 5
August 6
August 7
August 10
August 22
Concentrations Aloft
Site
Location
_.
—
—
—
West Chester, PA
West Chester, PA
Pottstown, PA
Pipersville, PA
Willow Grove NAS, P
Pottstown, PA
Pipersville, PA
Seabrook, NJ
Summit Field, DE
West Chester, PA
—
Time
(EST)
__
—
—
—
0930
0758
0631
0555
A 0919
0628
0577
1020
0535
0612
—
Concen-
tration
_.
—
—
—
0.060
0.050
0.030
0.030
0.035
0.020
0.015
0.020
0.060
0.060
—
Surface Concentrations
Site
Location
Summit Bridge, DE
Downingtown, PA
Lumberton, NJ
Van Hiseville, NJ
Lumberton, NJ
Van Hiseville, NJ
Lumberton, NJ
Van Hiseville, NJ
Downingtown, PA
Robbinsville, NJ
Downingtown, PA
Robbinsville, NJ
Downingtown, PA
Summit Bridge, DE
Downingtown, PA
Summit Bridge, DE
Downingtown, PA
Summit Bridge, DE
Downingtown, PA
Site
Number
1
2
3
5
3
5
3
5
2
4
2
4
2
1
2
1
2
1
2
Time
(EST)
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1100
1100
1000
1000
Concen-
tration
0.068
0.075
0.097
0.064
0.049
0.061
0.082
0.083
0.058
0.067
0.058
0.076
0.061
0.047
0.031
0.079
0.087
0.077
0.062
-------
Concentrations observed at the surface at the time of complete mixing tend to be
somewhat higher than concentrations measured aloft earlier. Although the bulk of ozone
production occurs during the late morning and early afternoon, some ozone is probably
produced between the time of the helicopter sounding and the time of the surface
concentrations shown in Table 34.
The measures of transport presented in Table 34 correspond to the geographical
extent of peak ozone concentrations in the study area. High transported levels imply
widespread levels later in the day. July 13, 19, and August 10 were the only case study
days on which surface concentrations higher than 0.08 ppm were observed during the first
hour of uninhibited vertical mixing. In addition, August 10 was the only case study day
during which average ozone concentrations of 0.06 ppm were reported aloft in the early
morning.
A review of peak surface ozone concentrations shows that July 13, 19, and
August 10 were also the only case study days in which high ozone levels were widespread
across the study area (i.e., more than five sites with concentrations > 0.12 ppm and ten or
more sites with concentrations > 0.10 ppm). Although the sample size is limited, the
implication is that significant nighttime ozone transport aloft can be a major cause of
high late-afternoon surface ozone concentrations in urban and rural areas.
5.2 OZONE LEVELS IN THE PHILADELPHIA URBAN PLUME
During the ten case study days, peak ozone levels did not always occur within the
urban plume. Table 35 summarizes the locations of peak ozone concentrations observed
with respect to Philadelphia. On five of the ten case study days, peak concentrations
were found downwind of Philadelphia under prevailing flow. On one occasion, the peak
concentration occurred upwind, on one occasion in Philadelphia, and on two occasions in
other areas. It should be pointed out that, while fourteen to fifteen monitoring sites were
generally operating in the study area, the peak concentration due to the urban plume
could have been missed, particularly when northerly flow prevailed. The frequency with
which peak ozone concentrations occur outside the urban plume is surprising. Some of the
conditions which contribute to this phenomenon were found to be:
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Table 35. LOCATIONS OF PEAK OZONE CONCENTRATIONS WITH
RESPECT TO PHILADELPHIA.
Date
July 12
July 13
July 16
July 19
August *
August 5
August 7
August 10
August 22
Peak Ozone Concentrations (in ppm)
Downwind
0.12*
0.123
0.151
0.157
0.102
0.135
0.120
0.129
—
Upwind
0.11*
0.1*1
0.067
0.10*
0.123
0.082
—
0.170
0.095
Philadelphia
Proper/
Cam den
0.111
0.161
0.100
0.138
0.130
0.120
0.122
0.137
0.1*0
Other
Areas
0.1*7
0.183
0.131
0.160
0.1**
0.119
0.129
0.12*
0.120
170
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o Surface advection of photochemical products from other uroan centers into
the study area (August 4 and 10).
o Very light or variable surface winds which cause high ozone levels in or near
Philadelphia Duly 13 and August 22).
o Surface transport from other high emission density areas in the study area
(July 12).
Of the five days during which peak ozone levels were found downwind of
Philadelphia, one day (August 7) experienced complete surface flow reversal so that no
true upwind area existed. For the remaining four days, the difference between upwind
and downwind ozone peaks ranged from 0.044 to 0.084 ppm. For this very small sample,
this 0.04 to 0.08 ppm range represents the additive effect of the urban plume, while the
late morning surface ozone levels representing ozone aloft (Table 34) were in the 0.05 to
0.08 ppm range.
5.3 MESOSCALE TRANSPORT
Mesoscale surface trajectories developed for the case study days revealed both local
(0 to 50 km) and mesoscale (50 to 100 km) surface transport. Table 36 presents the
locations of surface source areas for peak ozone levels and areas impacted by
Philadelphia's central business district emissions. These locations were determined from
surface trajectories. The central business district's emissions could be directly related to
study area peak ozone levels on three days: July 15 and August 5 and August 6. (It is
interesting to note that August 5 was a Sunday and August 6 a Monday. Downwind ozone
levels are virtually identical for the two days.) A source region outside the study area
was apparent on August 10 and suggested on August 4. High emission density areas within
the study area were possible source regions on July 12 and August 22. The source areas
for the remaining three case days (July 13, 19, and August 7) were rural or near rural
regions. July 13 and 19 showed evidence of high ozone levels aloft, while August 7 was a
puzzling case with a very pronounced flow reversal.
171
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Table 36. SOURCE AREAS FOR PEAK OZONE LEVELS AND AREAS IMPACTED BY EMISSIONS FROM
PHILADELPHIA'S CENTRAL BUSINESS DISTRICT AS DETERMINED BY MESOSCALE SURFACE
TRAJECTORIES.
Date
July 12
July 13
July 16
July 19
August 4
August 5
August 6
August 7
August 10
August 22
Peak
Ozone
(ppm)
0.147
0.183
0.151
0.160
0.144
0.135
0.136
0.129
0.170
0.140
Location
Ancora, NJ
Chester, PA
Downingtown, PA
Claymont, DE
Robbinsville, NJ
Ancora, NJ
Ancora, NJ
Lumberton, NJ
Claymont, DE
AMS Lab, Philadelphia
Source
Area
(0600 EST)
10 km SE of
Wilmington, NJ
25 km ESE of
Philadelphia
Central Business
District
15 km SE of
Lumberton, NJ
55 km NNE of
Robbinsville, NJ
Central Business
District
Central Business
District
5 km SW of
Lumberton, NJ
Baltimore/
Washington, D.C.
Claymont, DE
Area
Impacted by
Central
Business
District
20 km S of
Robbinsville, NJ
20 km NE of
Downingtown, PA
5 km NW of
Downingtown, PA
10 km W of
Downingtown, PA
40 km SSW of
Ancora, NJ
25 km SSE of
Ancora, NJ
20 km SE of
Ancora, NJ
15 km W of
Chester, PA
>100km NEof
study area
5 km NE of
Bristol, PA
Approximate
Ozone
Concen-
tration
(ppm)
0.12
0.12
0.15
0.16
0.12
0.14
0.14
0.12
>0.10
N)
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Ozone levels found downwind of the central business district were, in all cases, in
excess of 0.10 ppm. (No data were available for August 10 during which the central
business district's emissions were advected out of the study area.) On four of the case
study days, peak ozone levels downwind of the central business district were more than
0.03 ppm lower than the peak level observed in the study area.
5.* SYNOPTIC TRANSPORT
While the case study days were selected to provide a variety of prevailing flows, it
is interesting to note that these flows were spawned by a variety of synoptic situations
and that synoptic trajectories approached the study area in a variety of ways.
While most of the trajectories examined showed over-land paths, July 16 and 19
showed over-water paths. Six of the ten case study days demonstrated significant
anticyclonic curvature in the trajectory. Two of the days examined (July 19 and August 4)
demonstrated practically no relationship between trajectories in the 100- to 500-m and
1500- to 2000-m layers.
The three days on which the highest morning ozone levels were observed which
suggested synoptic transport were July 13 and 19, and August 10. The synoptic trajec-
tories, particularly low-level trajectories, showed evidence of tracks which passed upwind
over or near major urban areas.
5.5 DAYS RECOMMENDED FOR iMODEL VERIFICATION
To properly evaluate the effects of ozone control strategies on ozone concentrations
downwind of Philadelphia, cases in which ozone levels occur downwind of Philadelphia
must be selected for modeling. To give confidence to the results, the model must be
validated on these types of days. Of the ten case study days analyzed, the study area
peak levels occurred unambiguously downwind of Philadelphia on three days (July 16, and
August 5 and 6).
To consider the effects of transported versus locally-produced ozone, July 13, 19,
and August 10 are candidates for model verification. July 19 is especially suitable since
173
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very high ozone levels were recorded downwind of Philadelphia, while significant
transport aloft resulted in widespread high ozone levels.
Finally, for the most precise definition of boundary and initial conditions aloft, the
days with helicopter data must be considered: August 4 through 7, and August 10.
17*
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6. BIBLIOGRAPHY
Baxter, R., G.Y. Lowe, and T. Nguyen (1978): Acoustic Radar Chart Preparation and
Interpretation. AeroVironment Inc., Pasadena, California.
Chan, M.W., D.W. Allard, and I. Tombach (1979): Ozone and precursor transport into an
urban area: evaluation of measurement approaches. EPA-450/4-79-039.
Code of Federal Regulations, Volume 40, Title 50, Appendix F.
Federal Register (1978): Volume 44, Page 8221-8233, February 8.
Hancock, C.W. (1978): Philadelphia oxidant study, 1978 helicopter platform data report.
Northrop Services, Inc., Report No. E5G-TR-78-15.
Maynard, 3.B., and W.N. Sanders (1969): Determination of the detailed hydrocarbon
composition and potential atmospheric reactivity of full range motor gasolines.
3APCA 19, 7 (505-510).
Mayrsohn, H., 3.H. Crabtree, M. Kuramoto, R.D. Sothern, and S.H. Mano (1977): Source
reconciliation of atmospheric hydrocarbons 1974. Atmos. Environ. _H_ (189-192).
Reynolds, S.D., T.W. Tesche, and L.E. Reid (1978): An introduction to the SAI Airshed
Model and its usage. Systems Application, Incorporated, Report No. EF78-53R3.
Sanders, W.N. and 3.B. Maynard (1968): Capillary Gas chromatographic method for
determining the C^-C,-, hydrocarbons in full range motor gasolines. Anal. Chem.
40, 3 (527-535). J u
Stephens, E.R. (1973). Hydrocarbons in polluted air summary report. Coordinating
Research Council Project CAP A-5-68.
Westberg, H. and P. Sweany (1980): Philadelphia oxidant data enhancement study:
hydrocarbon analysis. Washington State University Chemical Engineering
Department, February.
175
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TECHNICAL REPORT DATA
{Please read Instructions on the re:iene before
REPORT NO.
EPA-450/4-81-011
13. RECIPIENT'S ACCESSION N <_>
<». TITLE AND SUBTITLE
- 5. REPORT DATE
Philadelphia Oxidant Data Enhancement Study •
Analysis and Interpretation of Measured Data
March 1981
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO.
Douglas Allard, Michael Chan, Chris Marlia, and Edgar Stephens ! AV-FR-80/588R
PERFORMING ORGANIZATION NAME AND ADDRESS
AeroVironment, Incorporated
145 Vista Boulevard
Pasadena, California 91107
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-3332
12. SPONSORING AGENCY NAME AND ADDRESS
Monitoring and Data Analysis Division
Office of Air Quality Planning and Standards
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Project Officer: Norman C. Possiel
16. ABSTRACT
The Philadelphia
ozone, precursor,
The data will be
1) to verify and
their use, and 2)
Oxidant Data Enhancement Study was conducted to obtain a data base of
and meteorological measurements in the vicinity of Philadelphia, PA.
used by the U.S. Environmental Protection Agency for two purposes:
apply various photochemical models and to help develop guidance for
to better understand the photochemical and meteorolonical processes
associated with peak ozone and N02 concentrations in the Philadelphia area. Philadel-
phia was selected for study because it is large enough to be capable of generating
high ozone levels, and it may be subject to significant ozone and/or precursor trans-
port. During the period of July 2, 1979 through September 18, 1979, AeroVironment, Inc
(AV) operated five surface monitoring stations in the vicinity of Philadelphia to
collect the required data. Eleven other surface monitoring stations operated by State
and local agencies collected data for inclusion in the data base. An instrumented
helicopter, operated by EPA's Environmental Monitoring and Support Laboratory in
Las Vegas, collected data aloft during a four-week period in July and August. In
addition, upper-air meteorological measurements were obtained by Beukers Labs. This
report describes the data collection efforts of AV and includes an analysis and
interpretation of the field study data base. The analyses are primarily directed
toward identifying the concentrations of ozone and precursors transported in the city
and ozone formed in the urban plume downwind.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Group
Ozone Measurements
Non-methane Hydrocarbon Measurements
Oxides of Nitroaen Measurements
Transport of Pollutants
Urban Plumes
Trajectory Analyses
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS fThis Report!
21 NO O F D A G e 5
187
20 SECURITY CLASS tThis paqei
122. PRICE
EPA Form 2220-1 (Rev. 4-77) PREV.OUS EOIT.ON 15 OBSOLETE
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