United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-84-011
August 1984
Air
Northeast Corridor
Regional Modeling
Project
Ozone and Precursor
Transport in New York
City and Boston During
The 1980 Field Program
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EPA-450/4-84-011
NORTHEAST CORRIDOR REGIONAL MODELING PROJECT
Ozone and Precursor Transport in New York City and
Boston During the 1980 Field Program
by
Norman C. Possiel*
Office of Air Quality Planning and Standards
Office of Air and Radiation
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
and
Chester W. Spicer, Philip R. Sticksel, and George M. Sverdrup
Battelle's Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
and
Abdul J. Alkezweeny and William E. Davis
Battelle's Pacific Northwest Laboratories
Box 999
Richland, Washington 99352
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
"On assignment from the National Oceanic and Atmospheric Administration
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DISCLAIMER
This report has been reviewed by the Office of Air Quality
Planning and Standards, EPA, and approved for publication. Mention of
trade names or commercial products is not intended to constitute endorsement
or recommendation for use.
ii
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CONTENTS
Page
Disclaimer ii
Fi gures v
Tables vi
Acknowledgments vi i
Executive Summary viii
1. Introduction 1
2. Program Scope 3
2.1 Selection of Case Study Days 5
3. Definition of Airflow on Study Days 7
3.1 Synoptic-scale Trajectories 7
3.2 Mesoscale Trajectories 7
4. Interpretation of Pollutant and Meteorological
Mea suremen ts 9
4.1 Pollutant Concentrations in the Urban Plumes 9
4.1.1 Maximum Pollutant Concentrations
from Morning Emissions 9
4.1.2 Diurnal Pollutant Concentration Profiles
in Urban Air Parcels 14
4.1.3 Transport Time and Distance to Peak
03 and N02 19
4.1.4 Downwind Distance to Background NOX 24
4.1.5 Plumes from Medium Size Cities Between New York
and Boston 26
4.2 Pol 1utant Transport 34
4.2.1 Analysis Procedure 34
4.2.2 Discussion of Ozone and Precursor Transport 35
4.3 Temporal Changes in Ozone Above the
Boundary Layer 43
i i i
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4.4 Comparison of Ozone Levels at the
Surface and Aloft 49
4.4.1 Comparison of Morning 03 Concentrations at
the Surface and Aloft 50
4.4.2 Comparison of Afternoon 03 Concentrations at
the Surface and Aloft 54
5. Concl us ions 59
References 64
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FIGURES
Number Page
1 The study region and the location of monitoring
stations included in this study 4
Time lines of air parcels crossing the New York City
urban area at 0600, 0800, and 1000 EST and diurnal
ozone concentrations at sites in the vicinity of parcel
tracks on July 22, 1980 10
Time history of air parcel leading to maximum ozone on
July 22, 1980 18
Flight track for Boston on the afternoon of
July 24, 1980 31
Ozone distribution aloft downwind of Boston on the
a fternoon of July 24, 1980 33
Surface ozone concentration isopleths (ppb), 0800 through
2200 EST, on June 24, 1980 41
Characteristic ozone profile types identified by
Ludwig et al 45
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TABLES
Mumber Page
1 Case Study Days Selected for Analysis 6
2 Maximum Pollutant Concentrations Generated in Air Parcels
Crossing New York City and Boston at Selected Times 12
3 Time, Position, and Concentration Profiles for Air
Parcels Generating Ozone Maxima 15
4 Times and Distances from New York City to Maximum Ozone 21
5 Times and Distances from Boston to Maximum Ozone 23
6 Times and Distances to Maximum N02 Aloft in the
New York City and Boston Urban Plumes 25
7 Distance at Which NOX in Plume Approaches Background
Concentration 27
8 Ozone and Wind Direction at Kent County, RI
on July 18, 1980 30
9 Transport Regimes on Case Study Days 36
10 Average Transported Ozone and Precursors for Corridor and
Non-Corri dor Flow Regimes 39
11 Temporal Variations in Ozone Aloft 47
12 Comparison of Mid-morning Surface Ozone With Early
Morning Ozone Aloft 51
13 Comparison of Afternoon Ozone Concentrations at the
Surface and Aloft in the New York Area . 55
14 Comparison of Afternoon Ozone Concentrations at the
Surface and Aloft in the Boston Area 56
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ACKNOWLEDGEMENTS
This report was prepared by EPA from the report "Analysis
and Interpretation of Ambient Measurements in New York and Boston from
the 1980 Northeast Corridor Regional Modeling Project" submitted by
Battelle's Columbus and Pacific Northwest Laboratories under Contract
68-03-2958. Additional analyses conducted by EPA to supplement the
original submittal have been included in this report. The assistance
of various EPA staff in reviewing the report, and the final typing by
Zada Nelson, Carol Bradsher and Carole Mask, are greatly appreciated.
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EXECUTIVE SUMMARY
This report describes the results of a 1-1/2 year study to analyze
portions of the data base obtained during the 1980 Northeast Corridor Regional
Modeling Project (NECRMP). The NECRMP data base was obtained primarily for
the application of urban and regional scale photochemical models to the
Northeast, including the major Corridor cities: Washington, DC; Baltimore;
Philadelphia; New York City; and Boston. Although the NECRMP data base pro-
vides data primarily for model application, the extensive data base is also
suitable for interpreting the meteorological and chemical processes which
influence 03 formation and transport.
The 1980 NECRMP data collection program involved extensive air quality
and meteorology measurements at the surface and aloft. Surface based meas-
urements available from selected sites in the Northeast Corridor include 03,
NO/NOX, NMOC, wind speed, wind direction, temperature, solar radiation, and
hydrocarbon species. In addition, upper air meteorological measurements were
obtained by rawinsonde soundings, sodar, and pilot balloon observations.
Instrumented aircraft were operated in the New York and Boston areas to
obtain measurements aloft of 03, NO/NOX, bscat, temperature, and relative
humidity. The protocol for aircraft monitoring flights required vertical
profiling of the atmosphere upwind of the city in the mornings and mapping
of the urban 03 plumes in the afternoon. Surface based measurements were
made throughout the summer, while aircraft monitoring was limited to the
period from mid-July through mid-August.
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The present study focuses on 20 days of the 1980 NECRMP data base.
These case study days were divided between New York City (12 days) and
Boston (8 days) and were selected to provide for analyses of the following
three meteorological situations:
0 moderate wind speeds with wind directions conducive to interurban
transport between Corridor cities;
0 moderate wind speeds with wind directions from sectors for which
interurban transport is unlikely; and
0 weak flows and stagnating or near stagnating conditions.
The interpretive effort was designed to address a number of questions and
issues relating to 03 formation and transport in the Northeast Corridor.
These include:
1. Do concentrations of 03 and precursors tranported into New York
City and Boston differ during along-Corridor and non-Corridor
transport regimes?
2. What is the diurnal variation of 03 and precursors in air parcels
leading to the maximum ozone concentration in the urban plume?
3. What is the average transport time and distance to maximum 03 in
the urban plume? What is the typical downwind distance to maximum
N02 in the urban plume?
4. What is the typical downwind distance to where NOX in the urban
plume becomes indistinguishable from background concentrations?
5. Can mid-morning surface 03 measurements be used to estimate
early morning upwind 03 aloft?
6. Can mid-day aircraft measurements of 03 be used to estimate
surface concentrations for areas between measurement sites?
7. Does 03 aloft, initially isolated from the effects of surface
emissions and scavenging, change substantially prior to the
dissipation of the nocturnal inversion when pollutants aloft
are mixed to the surface?
8. Is there evidence in the data of 03 plumes from medium size
cities such as Bridgeport, New Haven, and Hartford, CT or
Providence, RI?
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A summary of the study and the important findings pertinent to these
questions are presented below.
1. Do concentrations of 63 and precursors transported into New York
City and Boston differ during along-Corridor and non-Corridor
transport regimes?
The transport of 03 and precursors into New York City and Boston was
examined for the surface layer and for layers aloft. Although the analysis
was to have categorized each day according to one of three flow regimes,
intepretation of trajectories and pollutant measurements indicates that more
than one type of flow regime occurred on about half of the case study days.
On such days the direction of transport was rather complex and varied with
time and altitude. Typically, overnight transport in the surface layer was
along the Corridor, whereas aloft, above the. nocturnal inversion, transport
was from areas west of the Corridor.
Measurements at the surface and aloft were partitioned and averaged by
flow regime with the following results. For New York City, morning precursor
concentrations transported into- the urban area at the surface were twice as
high with along-Corridor transport than when transport was from outside the
Corridor. Aloft, precursor concentrations, particularly NMOC, were also much
higher when transport was along the. Corridor. The analysis indicates that
high morning precursor concentrations transported into the New York area with
along-Corridor flow were attributable to overnight emissions in the Philadelphia
area. During mid-afternoon the impact of the Philadelphia 03 plume was typically
observed at one or more monitoring sites on the upwind (southwest) fringe of
New York City.
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In Boston, there was little difference in surface precursor concentrations
during along-Corridor versus non-Corridor transport regimes. However, the con-
centration of NMOC aloft during along-Corridor transport was triple the magni-
tude of aloft concentrations when transport was from outside the Corridor.
Average 03 aloft transported into Boston during the morning was also higher
with along-Corridor flow (100 ppb versus 76 ppb). The impact of the New York
City 03 plume on portions of the Boston area was observed during the evening
across the upwind (southwest) fringe of Boston on days when transport was
along the Corridor.
2. What is the temporal pattern of 03 and precursors in the air
parcel containing the maximum ozone concentration in the urban
piume?
Mesoscale trajectories and surface measurements were used to determine
the temporal pattern of 03, NO, N02, and NMOC in the air parcel which con-
tained the maximum 03 observed within the urban plume on each study day. In
New York City, the concentration of 03 decreased as the air parcel traveled
from upwind rural and suburban locations into the urban area in the morning,
then increased rapidly later in the morning as the air parcel departed the
city and the rate of photochemical reactions increased. In almost every
case, the maximum 03 concentration in the plume occurred between 1300 and
1500 EST. (In general, after 1500 EST, UV intensity decreases, and the rate
of dilution overcomes the rate of 03 production such that the air parcel 03
concentration also begins to decrease.) The concentrations of NO, N02, and
NMOC generally increased as the air parcel approached the city in the morning.
After leaving the city, the nitrogen oxide concentration fell, most likely
due to dilution and chemical conversion to HN03, PAN, and particulate nitrate.
XI
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Unfortunately, there were insufficient NMOC sites to judge the temporal pattern
downwind beyond the urban area. Hourly concentrations of 03, NO, N02, and
NMOC are provided for ten of the case study days in Section 4.1.2. (Analyses
pertaining to the temporal pattern of 03 and precursors in the Boston plume were
very limited since the plume was transported offshore on all but one case study
day).
3. What is the average transport time and distance to maximum 03
in the urban plume? What is the typical downwind distance to
maximum N02 in the urban plume?
Surface measurements of 03, NO/NO?, and NMOC were examined in conjunction
with mesoscale trajectories to determine the maximum pollutant concentrations
formed in air parcels crossing the urban centers of New York City and Boston
during the morning when precursor emissions are greatest. For New York City,
the results indicate that the highest 03 concerttrations were associated with air
parcels crossing the city at approximately 0800 EST. On the average, air par-
cels crossing the city at 0600 EST yielded maximum 03 of 152 ppb at 1300 EST,
parcels crossing at 0800 EST generated an 63 maximum of 219 ppb at 1400 EST,
and those crossing at 1000 EST showed a maximum 03 concentration of 211 ppb
occurring at 1500 EST. (Only one day was analyzed for Boston since the urban
plume was transported offshore on the other case study days.)
The data base was analyzed to determine the distance and travel time
from the center of both New York City and Boston to the location of the peak
03 concentration in the urban plume. For New York City, the average downwind
distance to maximum 03 measured at the surface was 93 km, with an average
transport time of just over 5 hours. The average distance and travel time to
peak 03 aloft was 110 km and 6.5 hours, respectively. In the Boston area,
aircraft data provided the most useful information relative to this question
xii
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since the urban plume was transported over the ocean on all but one case
study day. The aircraft data indicate that the average distance to the 03
maximum aloft was 81 km, with a range of 61 to 107 km. The average transport
time to peak 03 was 4 hours.
The analysis indicates that maximum surface concentrations of NO and N0£
are found within or shortly downwind of the urban center. For most cases
studied, the highest concentrations of NO and N02 were associated with the air
parcels crossing the city at 0800 EST. Aloft, the distance to maximum N02
downwind during mid-day ranged from 23 to 48 km in New York City and 34 to 110
km in Boston. Estimated transport time to maximum N02 was 1 to 3 hours for
both urban areas.
4. What is the typical downwind distance to where NOX in the urban
plume becomes indistinguishable from background concentrations?
For three days in Boston and two days in New York City, the distance
from the urban area to the point where the urban plume NOX concentration
aloft became indistinguishable from the air mass background NOX concentrations
were estimated. This distance ranged from 85 to 165 km. The estimated travel
time to background NOX ranged from 5.5 to 12 hours.
5. Can mid-morning surface 03 measurements be used to estimate
early morning upwind 03 aloft?
Measurements of 03 at the surface and aloft, and sodar-derived mixing
heights were analyzed to determine whether mid-morning surface 03 measure-
ments during the period when the nocturnal inversion is dissipating can yield
information on 03 concentrations aloft prior to inversion break-up. The analy-
sis indicates that average surface 03 concentrations upwind (3-hour average
centered around the time of inversion dissipation) do represent early morning
03 concentrations aloft on many study days. However, there were also a number
xm
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of cases when such an assumption would, lead to significant underestimation (or
overestimation) of the early morning levels aloft. In these cases, it appears
that 03 aloft transported into the city had actually increased (or decreased)
between the time of the early morning aircraft measurements and the time
of inversion dissipation. This may have been due to reactions among 03 and
transported precursors or to spatial variations in 03 aloft transported across
the urban area. Thus, using surface data for estimating early morning con-
centrations aloft should be done with caution, particularly in situations where
urban areas are in fairly close proximity or high concentrations of transported
precursors are expected.
6. Can mid-day aircraft measurements of 03 be used to 3Stimate
surface concentrations between measurement sites?
Afternoon surface 03 measurements were compared to mid-boundary layer
(~ 800m) aircraft measurements made in the vicinity of surface monitoring
stations. The results indicate that, in locations where the atmosphere appears
to be well mixed, the surface and aircraft data agree within 10 to 15 ppb.
However, large differences were, observed between surface and aircraft data in
most comparisons near the edge of urban plumes, and in conjunction with the
internal boundary layer produced by sea breeze wind flows. These differences
were the result of strong vertical and horizontal concentration gradients
associated with such features. It is concluded that aircraft data should be
used with caution for estimating surface concentrations in areas subject to
sea breeze circulations or other mesoscale meteorological flows, and in areas
of large gradients at the edge of urban plumes. However, mid-day aircraft
data can provide a reasonable estimate of area-wide surface 03 concentrations
away from the preceding complex situations.
xiv
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7. Does 03 aloft, initially isolated from the effects of surface
emissions and scavenging, change substantially prior to the
dissipation of the nocturnal inversion when pollutants aloft
are mixed to the surface?
Temporal variations in 63 concentrations aloft, in air parcels isolated
from boundary layer influences (e.g., emissions, scavenging, etc.) were investi-
gated using aircraft pollutant and meteorological measurements. The results
indicate that, in most of the cases examined, 03 concentrations aloft were
fairly stable (within ± 5 ppb) between early morning (0500/0600 EST) and
mid-morning (1000/1100 EST) measurements within an air parcel. However, 03
production was evident in those air parcels containing comparatively high air
mass NOX concentrations and probably other 03 precursors, as indicated by the
aerosol content and estimated track of the air parcel relative to upwind urban
areas.
8. Is there evidence in the data of 03 plumes from medium size
cities such as Bridgeport, New Haven, and Hartford, CT or
Providence, RI?
The surface and aircraft data were examined in an attempt to identify
03 plumes from other smaller Corridor cities, such as Bridgeport, New Haven,
and Hartford, CT, and Providence, RI. In general, it was difficult to
define 03 plumes from such cities due to the relatively high air mass 03
levels, the complexity of airflow patterns, and the frequent incursions of
urban plumes from the major Corridor cities. Also, since the monitoring
program was not directed toward investigating these cities, comparatively
little data were available for this type of analysis. However, on two occa-
sions, there was evidence of the Providence 03 plume from the Boston area
aircraft data. In the clearest example, 03 in the Providence plume was
20 to 30 ppb higher than the air mass 03 concentration upwind of both cities.
xv
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SECTION 1
INTRODUCTION
Investigations since the mid-1970s have demonstrated that ozone (03)
is a pervasive contaminant of air over the northeastern United States. 1-5
Studies have shown that ambient concentrations exceeding the 0.12 ppm (120 ppb)
National Ambient Air Quality Standard (NAAQS) level for 03 are observed in many
parts of the Northeast, and concentrations up to 300 ppb have been observed
downwind of cities in this highly urbanized corridor. Also, ozone concentra-
tions exceeding the NAAQS are frequently observed over a large portion of the
region, and field study results have shown that both interurban and long
distance transport of 03 and its precursors should be considered in designing
control strategies.
In order to devise effective and equitable strategies for reducing the
concentration of 03 in the Northeast, the Environmental Protection Agency (EPA)
has been conducting a major long-term program with both field measurement and
modeling components. The field measurement programs associated with the
Northeast Corridor Regional Modeling Project (NECRMP) were designed to develop
a data base for regional/urban model verification/application, as well as to
improve understanding of the chemical and meteorological phenomena resulting in
high regional 03 concentrations. The major urban data collection program of
NECRMP was conducted during the summer of 1980. The purpose of that effort was
to obtain a data base for the application of the Airshed^ urban photochemical
model to Northeast Corridor cities, including Washington, DC, Baltimore, New
York City, and Boston. Regional monitoring studies were also conducted during
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1980 as part of NECRMP. Although NECRMP was designed primarily to provide
data for model application, the extensive data base is also suitable for
interpretation of meteorological and chemical processes which influence 03
formation and transport.
This report describes the results of a program designed to address a
number of questions and issues relating to 03 formation and transport in the
New York City to Boston portion of the Northeast Corridor. These questions/
i ssues include:
1. Do concentrations of 03 and precursors transported into New York City
and Boston differ during along-Corridor and non-Corridor transport
regimes?
2. What is the diurnal variation of 03 and precursors in air parcels
leading to the maximum 03 concentration in the urban plume?
3. What is the average transport time and distance to maximum 03 in
the urban plume? What is the typical downwind distance to maximum
N02 in the urban plume?
4. What is the typical downwind distance to where NOX in the urban plume
becomes indistinguishable from background concentrations?
5. Can mid-morning surface 63 measurements be used to estimate early
morning upwind 03 aloft?
6. Can mid-day, aircraft measurements of 03 be used to estimate surface
concentrations in areas between measurement sites?
7. Does 03 aloft, initially isolated from the effects of surface emissions
and scavenging, change substantially/ prior to the dissipation of the
nocturnal inversion when pollutants aloft are mixed to the surface?
8. Is there evidence in the data of 03 plumes from medium size cities
such as Bridgeport, New Haven, and Hartford, CT or Providence, RI?
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SECTION 2
PROGRAM SCOPE
The 1980 NECRMP urban measurement programs in New York and Boston included
extensive air quality and meteorological measurements at the surface and aloft.
Surface-based measurements available from sites in the Northeast Corridor
include 03, nitric oxide/nitrogen dioxide/oxides of nitrogen (NO/N02/NOX),
nonmethane organic compounds (NMOC), wind speed, wind direction, temperature,
solar radiation, and hydrocarbon species. In addition, 30-minute average
mixing heights were derived from monostatic sodar, and temperature and/or winds
above the surface were obtained by rawinsonde soundings and pilot balloon
observations (pibals). Measurements made aloft by instrumented aircraft in
the New York and Boston areas include 03, NO/NOX, light scattering coefficient
(bscat), temperature, and relative humidity. Surface-based measurements were
made throughout the summer, while aircraft monitoring was limited to the period
from mid-July through mid-August. A map of the study area is shown in Figure 1
along with the location of surface monitoring sites included in this analysis.
The present study was designed to analyze 20 days of the 1980 NECRMP data
base. These case study days were selected to provide for analysis of the
following three meteorological situations:
(1) moderate wind speeds with wind directions conducive to interurban
transport between Corridor cities;
(2) moderate wind speeds with wind direction from sectors for which
interurban transport is unlikely; and
(3) weak flows and stagnation or near stagnation conditions.
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5 «i«i
78*N 75*30« 7?M 71*JOM 71* H 7J*Mt4 7TH TnOH 7TH 7ITOM 71 M 70*30«
LONGITUDE
atoN 6TH aa*»M
Figure 1. The study region and the location of monitoring stations included in this study.
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The scope and organization of this report are linked directly to the
Statement of Work for Contract 68-03-2958, "Analysis and Interpretation
of Ambient Measurements in New York and Boston from the 1980 Northeast
Corridor Regional Modeling Project," conducted by Battelle's Columbus and
Pacific Northwest Laboratories.
2.1 Selection of Case Study Days
At the start of the program, 20 days were selected for analysis out of
the approximately 3 months of the 1980 NECRMP field program. These study
days were divided between New York City and Boston, and it was desired to
select days on which the airflow fit certain criteria. These criteria were
listed earlier and basically describe days on which interurban transport is
(1) likely, (2) unlikely, or (3) days of near stagnation. The data base for
the entire NECRMP study was screened to identify candidate study days meeting
the airflow criteria. Hourly surface wind speed, wind direction, and 03
concentration data were used, together with pertinent aircraft and upper air
wind measurements, to provide a preliminary classification of the candidate
days into the three airflow categories. From the list of candidate days meet-
ing the airflow criteria, final study days were selected using additional
criteria including the availability of aircraft data, completeness of the sur-
face data set, level of pollutant concentrations, etc. The New York area was
the focus of 12 days and Boston was the focus of 8 days. The study days are
listed in Table 1.
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Table 1. Case Study Days Selected for Analysis
New York ,Area
June 24 Tue. July 21* Mon. Augusts* Wed.
June 25 Wed. July 22* Tue. Augusts* Fri.
July 16* Wed. July 24* Thu. August 26 Tue,
July 18* Fri. July 31* Thu. August 28 Thu,
Boston Area
June 24 Tue. August 1* Fri.
July 15* Tue. August 5* Tue.
July 16* Wed. August 6* Wed.
July 17* Thu. Augusts* Fri.
*Aircraft data available.
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SECTION 3
DEFINITION OF AIR FLOW ON STUDY DAYS
3.1 Synoptic-Scale Trajectories
Synoptic-scale trajectories were used in this analysis to determine
the probable upwind source areas of 03 transported into New York City and
Boston, and the general downwind direction of urban plume transport. For-
ward and backward trajectories were prepared for five cities in the Northeast
Corridor: Boston; New York City; Philadelphia; Baltimore; and Washington, DC.
These trajectories were computed using the ATAD trajectory model
developed by Heffter et al.? The trajectory calculations were made from 6-hour
and 12-hour National Weather Service (NWS) upper air wind data averaged through
the layer from 500 to 1500m. Trajectories were computed in 3-hour increments,
backward and forward for 48 hours, from all five cities. In addition, forward
trajectories using wind data through the layer from 200 to 1000m were computed
for New York City, Philadelphia, and Washington, DC. The start/end time for the
forward/backward synoptic trajectories was 0700 EST.
3.2 Mesoscale Trajectories
Mesoscale forward and backward trajectories were computed for
points within the New York City and Boston urban areas. Used in the compu-
tation were 6-hour and 12-hour NWS upper air wind data, along with data from
*A revised version of this model is now available from Heffter.8 However,
because the trajectories in this analysis were computed for a fixed layer and
were not used to specify space/timem source/receptor relationships it is unlikely
that using trajectories computed with the revised model would alter the conclusions
of the study.
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the special rawinsonde soundings and plbal observations obtained as part of
the 1980 NECRMP ambient monitoring program. The pibal observations were
hourly, whereas the rawinsonde soundings were conducted at various times
between 0500-1500 EST. The winds were averaged over the appropriate layers
and interpolated hourly between measurement times to fill in missing data.
These data, in turn, were used to produce gridded wind fields covering the
area of interest. The interpolation and trajectory computation techniques
are based on procedures described by McNaughton, et al .9
Mesoscale trajectories were computed starting at 0600, 0800, and
1000 EST from each of three locations in the New York urban area and two
locations in Boston. Forward trajectories were computed hourly for 10 hours
and the backward trajectories for 5 hours for these locations and start times.
The back trajectories ending at 0600, 0800, and 1000 EST were used
to represent the flow above the nocturnal surface layer, upwind of the urban
area. The layer chosen for these trajectories was 250m to 1000m. The lower
limit of 250m was selected to avoid the effects of wind shear near the ground
during the early morning hours. For the forward trajectories, wind measure-
ments were averaged within the layer from 50m to the top of the boundary layer.
An estimate of the depth of the boundary layer on an hourly basis for each day
was developed from the available temperature soundings. These estimates rep-
resent the overland, convectively induced mixing heights in the area of
interest. For cases of a morning, surface based stable layer, a mixing height
of 250m was used.
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SECTION 4
INTERPRETATION OF POLLUTANT AND METEOROLOGICAL MEASUREMENTS
4.1 Pollutant Concentrations in the Urban Plume
Several characteristics of the New York City and Boston urban plumes were
examined as part of this task. These include the travel time and downwind
distance to peak concentrations of 03, NO, and N02 and the travel time and
downwind distance to where NOX in the urban plume diminished to the estimated
air mass background concentration. In addition, the data were examined for
evidence of 03 plumes from several medium size cities between New York City
and Boston.
4.1.1 Maximum Pollutant Concentrations from Morning Emissions
The objective of this task was to identify the maximum concentra-
tions of 03, NO, and N02 associated with air parcels crossing the urbanized
portions of New York City and Boston during the morning when precursor emis-
sions are at a maximum. The analysis procedure included the use of mesoscale
trajectories to estimate the downwind track of air parcels initially over the
city at each of three morning time periods: 0600; 0800; and 1000 EST. Iso-
pleth maps of 03 concentrations for various times during the day were used
to confirm the path of the urban plume. Time histories of 03 concentration
within each of the three air parcels were estimated from surface monitoring
data in the vicinity of the trajectory track using the procedure shown in
Figure 2. In this figure, the intersection of the heavy lines with the 03
diurnal profiles represents the 03 concentration in the air parcel that had
crossed the city at 0600, 0800, or 1000 EST as noted.
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240
July 22,1980
0800 1000
1200 1400 1600
Tim«, EST
1800
2000
2200
Figure 2. Time lines of air parcels crossing the New York City
urban area at 0600, 0800, and 1000 EST and diurnal
ozone concentrations at sites in the vicinity of
parcel tracks on July 22, 1980.
10
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As indicated in the example in Figure 2, the air parcels
containing morning emissions from New York City on July 22, 1980 were trans-
sported northeastward across Connecticut during the day and approached the
Boston area by evening. The maximum measured 03 concentrations were 169 ppb,
227 ppb, and 226 ppb along the 0600, 0800, and 1000 EST trajectories, respec-
tively. All of these values occurred in Connecticut.
Of the 20 case study days, 10 were excluded from this task because
the wind flow on those days transported the urban plume out over the Atlantic
Ocean away from surface monitoring sites. The maximum 03 concentration esti-
mated from morning emissions on the remaining 10 case study days are provided
in Table 2. Also shown in this table are the maximum concentrations of NO
and N02, along with times and locations of these maxima. Unfortunately, the
coverage available for NO and N02 is not nearly as comprehensive as for 03,
due to the much smaller number of stations which monitored these pollutants.
In any case, it is clear from Table 2 that both NO and N02 typically reach
their peak values within or shortly downwind of the urban area. Even though
N02 is being produced in the air parcels during the first hours of transport,
the rate of production is apparently overwhelmed by the rate of dilution. In
most cases, the highest concentrations of NO and N02 are associated with the
0800 EST air parcel.
Inspection of the 03 data in Table 2 reveals that the highest 03
maxima are associated with air parcels departing the city at 0800 EST. The
concentrations of 03 precursors in air leaving the city at 0600 EST are not
as high initially and are no doubt reduced even more than the later parcels
by dilution prior to the onset of extensive photochemical reaction. The
11
-------
Table 2. Maximum Pollutant Concentrations Generated in Air Parcels
Crossing Mew York City and Boston at Selected Times
Time of Air
Parcel Departure, Hax. 03
Date EST ppb
6-24-80
6-25-80
7-15-80
7-16-80
7-21-80
7-22-80
8-1-80
(New >York Source)
8-1-80
(Boston Source)
8-6-80
8-8-80
0600
0800
1000
0600
0800
1000
0600
0800
1000
0600
0800
1000
0600
.0800
1000
0600
0800
1000
0600
0800
1000
0600
0800
1000
0600
0800
1000
0600
0800
1000
140
220
230
160
275
180
160
190
145
180
230
290
175
240
303
170
220
225
122
140
125
110
145
125
125
250
190
140
205
215
Time
EST
1500
1530
1430
1400
1300
1430
1600
1500
1700
1200
1400
1400
1600
1300
1500
1300
1500
1400
1200
1300
1500
1100
1600
1130
1100
1300
1500
1330
1500
1630
Hax. NO
Location ppb
Kent Co.. RI
Mlddletown. CT
Stratford, CT
Mtddletown, CT
Stratford, CT
Stratford, CT
Georgetown, MA
Worcester, HA
Worcester, MA
Mlddletown. MA
Mlddletown, MA
New Haven, CT
Kent Co. , RI
Stony Brook, NY
Stratford, CT
Mlddletown, CT
Mlddletown, CT
Stratford, ,CT
Litchfleld, CT
Litchfleld, CT
l.itchfield, CT
Portsmouth, NH
Gardiner, ME
Sagamore Hill, MA
New Haven, CT
Stratford, CT
Stratford, CT
Kent Co., RI
Kent Co., RI
Kent Co., RI
051
037
005
038
005
061
025
009
068
006
Oil
040
Old
Oil
03U
026
004
054
010
002
040
005
005
057
039
002
065
039
003
Time
EST
0600
0800
1000
0600
1000
0600
0800
1000
0700
0800
1000
0700
0800
1000
0600
0800
1100
0600
0800
1000
0600
0900
1000
0600
0800
1100
0700
0900
1100
Location
Manhattan,
Manhattan,
'Manhattan,
Manhattan,
Manhattan,
Manhattan,
Manhattan,
Manhattan,
Queens, NY
Manhattan,
Manhattan,
Queens, NY
Manhattan,
Manhattan,
Manhattan,
Manhattan,
Queens, NY
Dumont , NJ
Manhattan,
Manhattan,
Max. N02 Time
ppb EST
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
East Boston, MA
Danvers, MA
East Boston
Manhattan,
Manhattan,
Queens, NY
Queens, NY
Queens, NY
Queens, NY
, MA
NY
NY
070
117
068
059
063
073
076
059
079
095
074 '
100
095
078
082
062
069
108
080
040
100
115
035
067
085
076
097
105
075
0600
0800
1000
0600
1000
0600
0800
1000
0700
1000
1000
0700
0800
1000
0600
0800
1100
0600
0800
1000
0600
0800
1000
0600
0800
1100
0700
0900
1100
Location
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Queens , NY
Glen Cove. NY
Manhattan, NY
Queens, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
Queens, NY
Manhattan, NY
Manhattan, NY
Manhattan, NY
East Boston, MA
East Boston, MA
East Boston, HA
Manhattan, NY
Manhattan, NY
Queens, NY
Queens, NY
Queens, NY
Queens, NY
-------
reduced photochemical activity is due to the relatively low solar intensity
at this early hour.
On the average, air parcels leaving New York City at 0600 EST
yielded maximum 03 of 152 ppb at 1300 EST, parcels departing at 0800 EST
generated an 03 maximum of 219 ppb at 1400 EST, and those leaving at 1000 EST
showed a maximum 03 concentration of 211 ppb, with the peak occurring at
1500 EST. The times of the maxima reflect the combined effects of reaction
time, solar intensity, and dilution. Reduced solar intensity and continuing
dilution in the late afternoon eventually overcome the effects of increased
reaction time, so that the highest concentrations on a given day usually
occur before 1600 EST.
On five of the 10 days analyzed (June 24 and 25, July 16 and 21,
and August 6), the trajectories indicate a westerly flow in the New York area
although the track of the surface 03 plume was to the northeast across
Connecticut into eastern Massachusetts, consistent with the low level wind
flow. Examinations of surface and upper air wind observations in the area
indicate that this situation may reflect the combined effects of the onshore
sea breeze circulation near the coast, coupled with topographic channeling of
the low level wind flow northward within the broad valley from New Haven to
Hartford, CT. As a result of this flow regime, the New York City plume on
these days was transported across Long Island Sound (and adjacent land areas
of coastal Connecticut and Long Island), then northeastward into central
Connecticut. Because the sea breeze flow is most pronounced within 400 to
500m of the surface it was apparently smoothed out in the mesoscale trajectory
computations which included winds through a much deeper layer.
13
-------
It should be noted that the diurnal profiles for sites along the
urban plume track provide strong prima facie evidence for 03 transport in
urban plumes. In nearly every case, the peak 03 concentration for each site
occurs at progressively later times along the plume track. In several cases,
the 03 maxima for the sites farthest downwind of the urban center occurred in
the late afternoon or evening after the sunlight intensity, the driving force
behind 03 production, had dropped off considerably, supporting the contention
that transport is the prime contributor to the observed peak 03 concentration.
4.1.2 Diurnal Pollutant Concentration Profiles in Urban Air Parcels
This task was aimed at determining the time history of 03, NO, N02,
and NMOC concentrations in air parcels which lead to the observed maximum 63
in the urban plume. In order to determine the time history of the pollutant
concentrations, the path of the air parcel leading to the maximum concentration
was determined from trajectories and isopleth maps as in the previous task.
With this information, monitoring stations in the vicinity of the air parcel
track were selected to provide the pollutant concentrations within the plume
at times prior to and after the observed maximum concentration.
As in the previous section, days were excluded from the analysis
if the urban plume was carried out over the ocean or over a land area with
few monitoring stations. This criterion resulted in the exclusion of most
Boston study days and some of the New York cases. However, data from two
additional days (July 15 and August 1) were included for the New York area
to supplement the analysis. The summary of 03 concentration time histories
is given in Table 3. Data on NO, N02, and NMOC are also tabulated, but these
data are limited by the fact that few of the monitoring sites for these
pollutants are outside the urban area.
14
-------
Table 3. Time, Position, and Concentration Profiles for Air Parcels Generating Ozone Maxima
Date
6/24/80
6/25/80
7/15/80
7/16/80
7/21/80
Time, EST
0600
0700/0800
0800/0900
1130
1400
1500
1700
0500
0600/0700
0700/0800
1030
1300
1600
0500
0600/0700
0700/0800
0900
1100
1300
1500
1730
0600
0800/0900
0900/1000
1100
1330
1400
1600
1800
0700
0800/0900
0900/1000
1100
1200
1400
1500
1700
1800
Location
New Brunswick, NJ
Linden/Bayonne, NJ
New York City, NY
Greenwich, CT
Stratford, CT
New Haven, CT
Middletown, CT
New Brunswick, NJ
Linden, NJ
New York City, NY
Greenwich, CT
Stratford, CT
Middletown, CT
New Brunswick, NJ
Linden/Bayonne, NJ
New York City, NY
Glen Cove, NY
Stratford, CT
Middletown, CT
Worcester, MA
Georgetown, MA
New Brunswick, NJ
Linden/Bayonne, NJ
New York City, NY
Queens, NY
Stratford, CT
New Haven, CT
Middletown, CT
Kent Co., Rl
New Brunswick, NJ
Linden/Bayonne, NJ
New York City, NY
Queens, NY
Glen Cove, NY
Stony Brook, NY
Stratford, CT
Middletown, CT
Kent County, RI
03, ppb
006
041
031
149
253
170
159
019
033
027
119
276
165
017
012
019
078
135
162
193
142
004
018
033
103
254
291
262
112
032
042
084
133
202
240
303
262
200
NO, ppb
029
015
027
004
___
012
032
005
010
032
041
003
...
041
020
025
006
---
013
004
008
002
005
__.
N02, ppb
058
043
100
022
...
040
072
022
---
032
057
076
045
---
056
054
080
055
031
032
064
046
015
~_ _
NMHC, ppbC
630
955
1890
----
....
420
1620
120
233
930
690
293
1125
300
360
1620
a Measurement below detectable Unit of the Instrument.
-------
Table 3. Time, Position, and Concentration Profiles for Air Parcels Generating Ozone Maxima (continued)
Date
Time, EST
Location
03, ppb
NO, ppb
N02, ppb
NMHC, ppbC
7/22/80
8/1/80
(NEW YORK)
8/1/80
(BOSTON)
8/6/80
8/8/80
0600
0600/0700
0700/0800
1000
1100
1300
1400
1500
1700
1900
0600
0600/0700
0700/0800
0900
1000
1200
1300
1500
0700
0800
1000
1200
1400
1600
2000
0500
0600/0700
0700/0800
0900
1000
1300
1400
0600
0700/0800
0800/0900
1030
1200
1300
1600
1830
New Brunswick, NJ
Llnden/Bayonne, NJ
New York City, NY
Glen Cove, NY
Greenwich, CT
Stratford, CT
New Haven, CT
Middle town, CT
Stafford, CT
Sudbury, MA
New Brunswick, NJ
Uinden/Bayonne, NJ
New York City, NY
Dumont, NJ
White Plains, NY
Oanbury, CT
Litchfield, CT
Agawam, MA
Medfield, MA
Boston, MA
Sagamore Hill, MA
Portsmouth, NH
Cape Elizabeth, ME
Gardiner, ME
Penobscot Co., ME
New Brunswick, NJ
Llnden/Bayonne, NJ
New York City, NY
Queens College, NY
Glen Cove, NY
Stratford, CT
New Haven, CT
New Brunswick, NJ
Linden/Bayonne, NJ
New York City, NY
Glen Cove, NY
Stony Brook, NY
Stratford, CT
Kent Co., RI
Easton, MA
005
009
025
064
127
213
227
220
197
134
004
018
032
049
062
120
140
075
058
073
103
127
133
143
082
009
017
021
052
085
249
168
003
034
031
084
143
246
222
095
032
020
034
008
003
036
027
017
013
007
LD«
LD
G17
014
030
006
LD
038
008
032
«
043
042
071
061
017
050
055
074
075
006
115
023
020
038
077
053
051
037
045
092
""
630
300
1298
810
495
810
0830
._
300
975
2168
578
2068
....
aMeasurement below detectable limit of the instrument.
-------
In New York City, data from five urban sites were used to
characterize 03 and precursor concentrations in the air parcel as it passed
within the urban area. Two-hour average concentrations were computed for two
urban sites in New Jersey (Linden and Bayonne) and for three urban sites in
New York (Manhattan, Astoria, and Brooklyn). These average values were used
to partially account for a decrease in the reliability of the trajectories
for estimating transport within the core of the urbanized area.
The data for July 22, 1980 were plotted as an example profile
from the data given in Table 3. The time history plot is shown in Figure 3.
This figure shows the concentrations of NO, N02» and 03 in the air parcel which
generated the highest surface concentration of 03 on this day. The time of day
is given along the bottom of the graph and the air parcel position along the
top. This particular parcel crossed northern New Jersey before 0800 EST and
the concentrations of NO and N02 increased as the air approached the metropol-
itan New York area. The NO reached a peak at 0800 EST directly over New York
City, whereas N02 appears to have peaked at 0900 EST on the downwind fringe of
the city. The level of NOX dropped off rapidly after the parcel left the
urban source area. In contrast, the 03 concentration decreased slightly as the
air parcel approached New York City in the morning but increased rapidly after
leaving the city. The rapid rise in 03 concentration occurred at the time the
sodar data indicate a rapid rise in the boundary layer. Morning vertical 03
profiles upwind of New York City indicate that the 03 concentration above the
surface based inversion averaged 56 ppb (650 to 1500m). Hence, photochemical
reactions, rather than mixing of 03 stored aloft overnight, must have been
responsible for the majority of the 03 generated on this day, although mixing
17
-------
0.30
0.12
0.10
0.08
O.OB
<
cc
cj
z
o
CJ
cvi
O
0.04
0.02
1200 1400
TIME (EST).hr
1600
1800
2000
Figure 3 Time history of air parcel leading to maximum ozone
on July 22, 1980.
18
-------
of 03 from aloft undoubtedly accelerated the photochemical reactions by
increasing the rate of NO oxidation to N02- On this day the maximum measured
03 concentration occurred at 1400 EST at New Haven, CT. As the air parcel
continued to move downwind throughout the afternoon and into the evening,
the 03 concentration decreased. Nevertheless, this same parcel was apparently
responsible for the maximum 03 measured at Stafford, CT (1700 EST), and at
Sudbury, MA (1900 EST).
In general, the data in Table 3 indicate that the concentration
of 03 decreased as the air parcel moved into the urban area in the morning,
due to processes such as chemical scavenging reactions. Ozone then increased
rapidly later in the morning as the air parcel left the city and the rate of
photochemical reactions increased. In almost every case, the maximum 03 con-
centration in the urban plume occurred between 1300 and 1500 EST. After 1500
EST, UV intensity generally decreases, and the rate of dilution overcomes the
rate of 03 production such that the air parcel 03 concentration begins to
decline slowly.
The concentrations of NO, N02, and NMOC generally increased as
the air approached the city in the morning. After leaving the city, the NOX
fell, likely due to dilution and probable chemical conversion to HN03, PAN,
and particulate nitrate. Unfortunately, there are insufficient MMOC data
to evaluate the time history of hydrocarbon concentrations.
4.1.3 Transport Time and Distance to Peak 03 and N02
To determine the distance and travel time from New York City and
Boston to the peak 03 and N02 concentrations measured in the urban plumes of
19
-------
each city, information on the location of maximum 03 prepared in the previous
section was enhanced with 03 and N02 meaurements aloft.
The times and distances to the maximum 03 concentrations at the
surface and aloft in the New York area are shown in Table 4. Because of the
complex flow during stagnation conditions on August 26, 1980, the transport
time was not computed. The surface data for three other days (July 18 and 31
and August 28) were also excluded from the analysis, because the northwest
flow aloft on these days transported the plume out over the Atlantic Ocean.
Recirculation of portions of the plume onshore in sea breeze flows later in
the day made it difficult to estimate travel distance and transport time.
The actual surface maximum may have occurred over the ocean.
Among the remaining days, the average downwind distance to maximum
03 at the surface was 96 km, with a mean transport time of just over 5 hours.
On the other hand, the average distance to peak 03 aloft was 110 km, with a
mean transport time of 6.5 hours. (Direct comparisons between the surface
and aloft values are somewhat misleading, because different days were involved
and day-to-day meteorology varied considerably.) In general, for the cases
studied, one can characterize the transport time to 03 maxima in the New York
City plume as 5 to 7 hours, with a typical downwind distance of 100 km.
For Boston, two difficulties were encountered in defining the
maximum 03 concentration within the urban plume. First, transport from upwind
sources was frequently responsible for the highest surface 03 concentration in
the Boston area. Second, on ocean transport days, when the plume was carried
offshore, the highest concentration in the plume may not have been measured,
even at coastal monitoring sites during sea breeze flows. These situations
20
-------
Table 4. Times and Distances from New York City to Maximum Ozone
Date
6/24/80
6/25/80
7/16/80
7/18/80
7/21/80
7/22/80
7/24/80
7/31/80
8/6/80
8/8/80
8/26/80
8/28/80
Site
Stratford, CT
Stratford, CT
New Haven, CT
a
Stratford, CT
New Haven, CT
a
a
Stratford, CT
Stratford, CT
Linden, NJ
New Brunswick, NJ
b
03 Max.,
ppb
(Ground)
253
276
291
303
227
...
...
...
249
246
188
188
...
Time,
EST
1400
1300
1400
1500
1400
1300
1300
1400
1300
Distance
90
90
110
90
110
...
...
90
90
U9
50
Transport
Time,
hours
5-6
5-6
4-5
5-6
5-6
...
...
5-6
4-5
...
...
03 Max.
PPb,
Aloftd
...
2156
249
...
223^
220
152e
269*
352
242
...
Time,
EST
1530
1420
1355
1700
1452
1627
1519
1322
Distance,
...
...
103
51
...
91
150
110
124
126
121
...
...
Direction
from
CHy
...
...
NE
SE
NE
NE
S
ESE
E
NE
...
Transport
Time,
hours
...
4
6
...
5
7-8
5-6
7
7
4
...
...
Location
near Derby, CT
south of Long Island
near Bridgeport, CT
near Middle town, CT
near Barnegat, NJ
south of Westhampton, LI
north of Riverhead, LI
over Long Island Sound
? Northwest air flow; maximum 03 over Atlantic Ocean.
D Recirculatlon air flow; maximum 0? may have occurred over Atlantic Ocean.
c Distance from Manhattan, NY.
d Measurement at 700-800m M5L unless otherwise noted.
e May not be maxima 0->; measurement listed was obtained on furthest downwind traverse of plume.
nay not oe maxim* uj; measurement MSI
f Measurement at 200n RSL during spiral.
g Measurement at urban site.
-------
were considered when interpreting the times and distances to maximum 03 given
in Table 5. For June 24, July 15, 16, 17, and August 6 and 8, the first site
listed is upwind, but in fact measured the highest concentration in the Boston
area. These values do not reflect the potential for 63 generation by emissions
in Boston. The second site is a coastal location. The 03 concentrations
listed for this site were measured during an onshore flow and thus provide a
lower limit estimate of 63 formed in the Boston plume (higher concentrations
may have occurred offshore). On August 1 and 5 transport from upwind urban
areas may have had a substantial contribution to maximum 63 at surface sites.
Thus, in the Boston area, aircraft data provide a more appropriate estimate
of 03 formation in the urban plume. The aircraft data in Table 5 show that
the downwind distance to maximum 03 in the Boston plume ranged from 61 to
107 km, with an average distance of 81 km. The mean transport time to peak
03 was 4 hours.
The times and distances to 03 maxima in the urban plumes of New
York City and Boston are useful pieces of information for the development of
control strategies, as well as for investigators who develop and test urban
models for these cities. Additional information of particular usefulness to
modelers relates to the transport time and distance to peak NOg. The concen-
tration of nitrogen oxides is especially sensitive to monitor locations,
because NO and N02 are primary pollutants (i.e., emitted directly to the
atmosphere). Nitrogen dioxide is also a secondary pollutant formed in the
series of reactions leading to 03 formation. In and around major urban areas,
the peak N02 concentration is usually observed near or shortly downwind of the
urban center, because surface monitoring stations are strongly influenced by
22
-------
Table 5. Times and Distances from Boston to Maximum Ozone
Date
6/24/80
7/15/80
7/16/80
ro 7/17/80
Co
8/1/80
8/5/80
8/6/80
8/8/80
03 Max.,
ppb
Site (Ground)
Medffeld, MA
Cape Elizabeth, ME
Worcester, MA
Cape Elizabeth, ME
Easton, MA
Cape Elizabeth, ME
Easton, MA
Cape Elizabeth, ME
Georgetown, MA
Gardiner, ME
Medfleld, MA
Tewksbury, MA
Easton, MA
Cape Elizabeth, ME
154
097
193
145
127
127
150
143
143
143
159
115
120
112
Time,
EST
2100
1500
1500
1400
1500
1400
1700
1700
1100
1700
1400
1300
2000
1200
Distance
km
(a)
150
(a)
150
(a)
150
(a)
150
42b
(d)
31
(a)
150
Transport
Time,
hours
(a)
7-8
(a)
4-5
(a)
6
(a)
5
2b
lib
(d)
2
(a)
5-6
03 Max.
PPb,
Aloftc
208
170
200
197
151
133
1706
232
173
156
Time.
EST
1538
1400
1700
1542
1648
1554
1525
1548
1448
1449
Distance,
km
(a)
65
(a)
107
(a)
61
104
66
68
93
Direction
from
City
--
SW
NE
SU
NE
SU
NE
NE
NE
NE
E
Transport
Time, Location
hours
...
(a)
2
(a)
4
(a)
4
6
5
4
3-4
near RI border
over Atlantic Ocean
near RI border
over Atlantic Ocean
near RI border
over Atlantic Ocean
over Atlantic Ocean
over Atlantic Ocean
over Atlantic Ocean
over Atlantic Ocean
* Maximum Oj occurred upwind from Boston and reflects daytime transport from upwind urban areas.
° Overnight transport aloft from upwind sources may have resulted In observed 63 max.
c Measurement at 700-800m MSL unless otherwise noted.
d Convergent air flow west of Boston; peak may have contribution from Boston and Providence.
e May not be max. 03; measurement listed was obtained on furthest downwind traverse of plume.
-------
nearby emission sources. This phenomenon was demonstrated earlier in Tables
2 and 3, which show that the maximum surface N02 concentration is nearly
always found within or on the downwind fringe of the urban area. In order to
determine the time and distance required to generate peak NOg by chemical
reaction, it is more appropriate to employ the aircraft monitoring data.
These data are much less sensitive to local surface emissions and, conse-
quently, are more representative of the chemical dynamics of photochemical
air pollution. However, these data suffer from a lack of measurements close
in to the urban area on several days. Table 6 lists the time, distance and
transport time to maximum N02 concentration aloft in the afternoon for the
New York study area. Nbximum N02 concentrations aloft rangeu from 30 to 87
ppb, and the downwind distance to peak N02 aloft ranged from 23 to 48 km.
Transport times ranged from 1 to 3 hours. In addition, on July 31 and August
6 relatively high N02 concentrations were measured far downwind (33 ppb at
102 km and 68 ppb at 125 km, respectively). In both cases, high levels of 03
were also present, and it is likely that a portion of the measured N02 was
actually present in the form of nitric acid and peroxyacetyl nitrate.
The transport times and distances to maximum N02 aloft in the
Boston area during the afternoon are also shown in Table 6. Peak N02 concen-
trations aloft were in the range from 17 to 49 ppb. The distances to peak
N02 were in the range of 34 to 110 km, with transport times of 1 to 3 hours.
4.1.4 Downwind Distance to Background NOX
The purpose of this task was to determine the downwind distance
from the city to where the NOX concentration in the urban plume becomes diluted
24
-------
Table 6. Times and Distances to Maximum NCL Aloft in the
New York City and Boston Urbam Plames
Date
NEW YORK
7/18/80
7/22/80
7/24/80
7/31/80
8/6/80
8/8/80
BOSTON
7/15/80
7/16/80
7/17/80
8/1/80
8/5/80
8/6/80
8/8/80
Time,
EST
1153
1205
1211
1204
1220
1218
1339 .
1543
1459
1500
1401
1425
1335
N02 Maximum,
ppb
87
76
34
30
76
75
20
19
17
23
49
23
18
Distance from
City, km
32
37
23
40
48
41
34
110
62
74
36
41
53
Transport Time,
hours
4.0
2.0
1.0
3.0
2.0
1.5
1.0
3.0
2.0
3.0
2.0
2.0
1.5
25
-------
to the point where it approaches the observed air mass background NOX
concentration. Unfortunately; there was insufficient spatial coverage of
surface NOX sites to permit assessment of this distance. However, aircraft
data are better suited to this purpose and were used in this task. It is
important, for purposes of this task, that fresh emissions of NOX into the
plume downwind of the city be excluded; otherwise, the NOX concentration
could actually increase with downwind distance. This criterion was met by
using flights which pass primarily over the ocean, where such emissions are
minimal. Two afternoon flights in the New York area arid three in Boston met
all of the criteria for this task and were used in the analysis. The urban
plume NOX concentrations from aircraft plume traverses were plotted versus
downwind distance, and a straight line fitted through the points and extra-
polated to the air mass background NOX concentration observed outside the
urban plumes. The results of this analysis are shown in Table 7.
The distance at which plume NOX reaches the background concentrations
(i.e., is indistinguishable from air mass background by the measurement method)
is obviously dependent on a number of variables, foremost of which are dilution
rate, reaction rates and wind speed. No direct measure of dilution or reaction
rate is available, but the afternoon boundary layer transport speeds estimated
from the trajectories are included in the table.' As expected, the highest
transport speeds are associated with the furthest distance to background NOX.
The travel time for NOX to reach air mass background concentrations ranged
from 5.5 to 12 hours, and the estimated travel distance was 85 to 165 km.
4.1.5 Plumes from Medium Size Cities Between New York City and Boston
Clearly defined 03 plumes have frequently been observed downwind
of major centers of population and industry on photochemically active days.
26
-------
Table 7. Distance at Which NOX in Plume Approaches Background Concentration
Date
City
Estimated Distance
Flight to Background
Number NOV, km
Transport
Speed
km-hr"1
7/18/80
7/24/80
7/24/80
8/5/80
8/6/80
New York
New York
Boston
Boston
Boston
5
15
18
31
32
85
165
100
95
100
7.0
20.0
18.2
12.5
18.0
27
-------
The contribution of medium size cities to the downwind 03 burden has been
studied infrequently. Several medium size cities are sources of 03 precursors
in the Northeast Corridor, but observation of 03 plumes from these cities is
likely to be difficult, due to the generally high background levels of 63 in
the region. Nevertheless, important insight into 03 formation and transport
processes in the region may be gained by identification of plumes from smaller
cities, and comparison of their plume characteristics with those from New
York City and Boston.
It was difficult to define plumes from small cities using surface
data, because the number and distribution of monitoring stations was nearly
always insufficient for this purpose. Aircraft data are mos^ appropriate for
this task, since complete upwind and downwind traverses can be made over a
relatively short time. Although a considerable number of aircraft flights
were conducted during the monitoring program, no flights were designed spe-
cifically for small city plume mapping. As a consequence, this analysis is
limited to those flights in which small city plumes were observed fortuitously.
The identification of 03 plumes from smaller cities in the study
region focused on Bridgeport, New Haven, Hartford, and Providence. Because
no data were collected to address the issue of small city 03 plumes specfi-
cally, all surface and aircraft data collected during NECRMP, were surveyed
without limiting the analysis to the 20 study days. From this examination two
possible cases of the Providence plume were identified in the data.
Case 1
There is an indication of an 03 plume from Providence, on July 18, 1980.
An examination of surface 03 concentrations indicates that the 03 level at the
28
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Kent County site is relatively high compared to surrounding sites. The time
series of 03 concentration and wind direction at Kent County is shown in
Table 8. At this site, 03 reached 95 ppb at 1800 EST, while the concentration
remained less than 80 ppb at the surrounding stations (Attleboro, Providence,
Hartford, and Middletown). Airflow on July 18 was generally from the north-
erly quadrant early in the day. However, the wind data in Table 8 indicate a
shift to southerly flow after 1600 EST. These data suggest a recirculation
of air during the day, such that Providence emissions were first transported
offshore then back onshore toward the Kent County site. This indicates that
the Providence plume was the primary cause of the elevated 03 levels at the
Kent County site. However, it could be argued that Boston area emissions
provided a contribution even though the mesoscale trajectories for July 18
indicate that Boston's plume passed south of Cape Cod during the day.
If we assume that a plume from Providence caused the peak values at Kent
County, then the increase in 03 above the air mass concentration was 30 ppb,
as judged by the concentrations at surrounding locations.
Case 2 ---
The second, and perhaps more definitive, case of the Providence plume
is evident on July 24, 1980. On the afternoon of this day, the Boston plume
was tracked to the south via aircraft. The zig-zag flight track is shown as
a solid line on a map of the area in Figure 4. The 03 concentration along
traverses C-D and E-F is also plotted on the map. At the western-most edge
of the traverse E-F, there is a peak in 03 which appears as a shoulder on the
major peak representing the Boston urban plume. The Boston plume is also
29
-------
Table 8. Ozone and Wind Direction at Kent County, RI on July 18, 1980
Hind Direction.
Time. EST Ozone, ppb Degrees
0800 45 340
0900 50 345
1000 58 350
1100 60 345
1200 60 50
1300 60 315
1400 60 335
1500 62 35
1600 85 100
1700 90 170
1800 95 210
30
-------
o,.p*
Figure 4. Flight track for Boston on the afternoon of July 24, 1980.
31
-------
seen centered along traverse C-D but, 1n this case, there is no shoulder at
the western edge. The two traverses show that 63 concentrations upwind of
Providence, and outside the Boston plume, are 55 to 60 ppb, while downwind
in the Providence plume 03 is 75 ppb. These concentrations are replotted
in Figure 5 as shaded contours. This diagram shows even more clearly the
distinction between the Boston and Providence plumes.
The mesoscale trajectories for 1000 EST on July 24, also shown in
Figure 5, indicate the position of the Boston plume at 1400 EST. Comparison
of the ozone plume with the trajectories suggests that the Boston plume center
line and the trajectory track are in exact agreement. If ve assume a parallel
trajectory from Providence, the plume from this city would be expected in pre-
cisely the location where the shoulder was observed. The estimated 03 for the
Providence plume on July 24 was 15 to 20 ppb above the upwind concentration.
Examination of the NECRMP data did not reveal plumes from Hartford, New
Haven, and Bridgeport, CT. The technical problems of identifying such plumes
are compounded by the proximity of cities in this area and the complex meteor-
ology introduced by the land/sea interface. The increase in 03 in the two
instances when a Providence plume was identified ranged from 15 to 30 ppb.
This range can be compared with the increase in 03 observed in the plume of
a city of slightly smaller size in the Midwest. A study of the Springfield,
IL plume on a photochemically active day in the summer of 1977 revealed an
increase in 03 of 30 ppb above the air mass 03 concentration.1^ Thus, the
contribution to the downwind 03 burden of these two moderate size cities was
similar under these particular meteorological conditions.
32
-------
Figure 5. Ozone distribution aloft downwind of Boston
on the afternoon of July 24, 1980.
33
-------
4.2 Pollutant Transport
The objectives of this task were: (1) to quantify the concentrations of
03 and its precursors transported into and across the New York City and Boston
areas on the case study days; and (2) to identify the transport direction on
each day and infer the probable source area of 03 and precursors outside the
New York City and Boston urban plumes. These objectives are addressed
concurrently in this section.
For both New York City and Boston, surface and aircraft data were used
to determine the concentrations of pollutants transported into and across the
urban area during each case study day. Ozone measurements downwind of the
urban area, but outside the urban plume were also examined to evaluate the
homogeneity of air mass 03 concentrations transported across the region. The
probable source area for the observed transported concentrations was inferred
by interpretation of synoptic and mesoscale trajectories, and the surface and
upper air wind data.
4.2.1 Analysis Procedure
Analysis of pollutant concentrations upwind and downwind but
outside the urban plume of New York City was conducted for the case study
days: June 24, 25; July 16, 18, 21, 22, 24, 31; and August 6, 8, 26 and 28.
In Boston, the analysis was conducted for June 24; July 15, 16, 17; and
August 1, 5, 6, and 8. For these days, pollutant concentrations were examined
for three specific time periods in order that temporal patterns of pollutant
transport might be observed: morning (0600-1000 EST); mid-day (1200-1600 EST);
and evening (1800-2200 EST). First, surface winds and the trajectories were
interpreted to determine a boundary layer transport wind direction for each
time period. The transport wind directions were used to identify surface
34
-------
sites upwind or downwind outside the urban plume. For these sites, average
concentrations of 63, NO, N02, and NMOC were computed for each of the three
time periods. Data were not averaged for the entire 4-hour period when
large temporal concentration gradients were observed. Rather, an average
range was computed for the time period.
The concentrations of 63, NO, and N02 aloft were estimated from
aircraft spiral and transect data collected during flights in the vicinity
of each city. Upwind/downwind directions were determined from trajectories
and upper air winds. The spirals were divided into two or three vertical
segments depending on concentration gradients, and layer average concentra-
tions were calculated for each pollutant. Since no afternoon upwind aircraft
spirals were made in the New York area, measurements made during horizontal
flights over northeastern New Jersey were used for estimating upwind concen-
trations aloft. The concentrations of 03, NO, and N02 aloft downwind, but
outside the urban plume, were obtained by computing a spatial average con-
centration for each pollutant from portions of downwind transects that were
outside the plume.
4.2.2 Discussion of Ozone and Precursor Transport
This analysis was to have grouped each case study day into one of
three distinct flow regimes: Corridor transport; transport from outside the
Corridor; and near-stagnation/recirculation. The results, as summarized in
in Table 9, indicate that more than one type of flow regime occurred on many
of the days. Often, the direction of transport into New York City and
Boston varied by time of day and/or altitude. For example, on four days,
35
-------
Table 9. Transport Regimes on Case Study Days
Urban Area
New York City
Boston
Day
6/24/80
6/25/80
7/16/80*
7/18/80
7/21/80*
7/22/80'
7/24/80
7/31/80*
8/6/80
8/8/80*
8/26/80*
8/28/80*
6/24/80*
7/15/80*
7/17/80*
8/1/80
8/5/80*
8/6/80
8/8/80*
Flow Regime
Along-Corridor Transport
Along-Corridor Transport
Along-Corridor Transport, except
morning transport aloft from
outside the Corridor
Non-Corridor Transport
Along-Corridor Transport, except
morning transport aloft from
outside the Corridor
Along-Corridor Transport, except
morning transport aloft from
outside the Corridor
Non-Corridor Transport
Non-Corridor Transport/
Recirculation Flow
Non-Corridor Transport
Along-Corridor Transport, except
morning transport aloft from
outside the corridor
Near-Stagnation Conditions
Near-Stagnation Conditions
Morning: Non-Corridor Transport
Afternoon: Along-Corridor Transport
Along-Corridor Transport, except
morning transport aloft from
outside the Corridor
Morning: Non-Corridor Transport
Afternoon: Along-Corridor Transport
Along-Corridor Transport
Recirculation Flow
Along-Corridor Transport
Morning: Non-Corridor Transport
Afternoon: Along-Corridor Transport
''Flow regime varied with height and/or time on these days.
36
-------
overnight transport into the New York area at the surface and aloft up to
several hundred meters, was from along the Corridor. However, at higher
altitudes up to 1500m transport was from the west, beyond the Corridor. On
such days, a plume of high N02 and NMOC concentrations was observed during
early morning in the layer of along-Corridor flow with much lower concentrations
aloft in the layer transported from outside the Corridor. As the daytime
boundary layer grew, pollutants from both layers were eventually entrained,
and became mixed with precursors from surface emissions. Thus, on such days
pollutants transported from source areas both within and beyond the Corridor
participated in 63 formation in the New York area.
The estimated concentrations of 03, NO, N02, and NMOC transported
into and across the New York and Boston areas are summarized by flow regime
in Table 10. The vertical partitioning of pollutant concentrations aloft into
different flow regimes was typically made at an altitude between 500 and 1000m.
The partitioning on a particular day was based upon the vertical variation in
wind direction, vertical gradients in pollutant concentrations, and the track
of layer-averaged trajectories. Measurements from sites affected by recircu-
lation flows (in which pollutants are transported back over areas that previ-
ously had been upwind), and days with near-stagnation conditions (when upwind/
downwind areas are difficult to define) are not included in the table. Also
excluded are (1) morning 03 concentrations at the surface which may have been
affected by variations in local scavenging affects, and (2) mid-day precursor
concentrations which were low compared to early morning concentrations.
For New York City, the data indicate that morning precursor
concentrations at the surface resulting from along-Corridor transport were
about twice the concentration on days with transport from outside the Corridor.
37
-------
Aloft, precursor concentrations, particularly NMOC, were also much higher in
layers transported along the Corridor. These precursors appear to be the
result of overnight emissions in the Philadelphia area or other portions of
the Corridor upwind of New York City. Fairly large spatial and temporal var-
ations in morning NO and N02 concentrations were observed among monitoring
sites upwind of New York on most days, as indicated by the range in average
concentrations for these pollutants given in Table 10. This likely reflects
the combination of several factors including variations in the dispersion and
transport of overnight emissions within and just above the nocturnal surface-
based stable layer. (Spatial variations in NMOC could not be assessed since
only one NMOC site was operated upwind of New York.)
Mid-day 03 concentrations transported into New York City with
along-Corridor flow were 15 to 30 ppb higher at the "close-in" upwind sites
(i.e., sites over northern and central New Jersey 60 to 90 km from mid-
Manhattan) than at other sites further upwind (beyond -100km). The elevated
03 concentrations at these "close-in" sites, are likely the result of emissions
in suburban areas on the fringe of the main Corridor cities. Also, on Corridor
transport days, the direct impact of the Philadelphia 03 plume was typically
observed during mid-afternoon at one or more of these "close-in" upwind sites.
However, as the Philadelphia plume traveled across the New York urban area
surface 03 concentrations declined due to reaction with fresh NO emissions.
In Boston, there was little difference in the magnitude of surface
precursors during Corridor and non-Corridor transport regimes. Aloft, however,
the concentration of NMOC during Corridor transport was three times the magnitude
of NMOC when transport was from outside the Corridor. Also, incoming 03 aloft
38
-------
Table 10. Average Transported Ozone and Precursors for Corridor and
Non-Corridor Flow Regimes
Morning Precursors, ppb
Transport Regime
NO
Surface3
NO 2
NMOC,
ppbC
Aloft
NO N02
NMOC,
ppbC
Ozone, ppb
Morning
Upwind
Aloft '
Mid- day
Outside Urban Plume
Upwind Downwind
New York City
LDd-021 014-034
567
Corridor Transport
LD-006 043 285
089-116 076-089
Boston
LD-013 LD-019
LD-009 LD-009
Transport from Beyond Corridor
278 LD LD-013 048
219
Corridor Transport
LD 013 108
070 b
100
074-084"
085-098
. c
009
LD-008
Transport from Beyond Corridor
285 LD LD-012 036
076
a 0600-1000 EST
b Excludes measurements on July 24, 1980 which were unrepresentatively low compared to data for the other six days
in this category. Morning upwind 03 aloft was 035 ppb and mid-day 03 was 040 - 049 ppb. Trajectories indicate
48 hour transport from Southeast Canada on this day.
c Only two days in this transport category with mid-day downwind data: July 24 with 03 of 040 - 050 ppb, and
August 6 with 03 of 075 - 085 ppb.
d Concentration at or below the lower detectable limit of the monitor.
39
-------
during the morning on Corridor transport days averaged 100 ppb, compared to
76 ppb when transport was from outside the Corridor. It is interesting to
note that the average concentrations of surface NMOC, and the average concen-
tration of 03, NO, N02, and NMOC aloft are of similar magnitude upwind of New
York City and Boston during transport from areas outside the Corridor. This
suggests regional homogeneity in 03 and precursors on the days when transport
was not along the Corridor.
The impact of the New York City 03 plume on the Boston area was
observed at sites upwind of Boston and/or aloft during the late afternoon or
evening on most Corridor transport days. The 1-hour maximum surface 03 con-
centration upwind of Boston associated with boundary layer urban plume trans-
port ranged from 120 ppb (August 8) to 193 ppb (July 15). Aloft, transported
03 during the afternoon was as high as 200 ppb near the Massachusetts - Rhode
Island border on July 16.
An example of daytime 03 transport from the New York area to Boston
is shown in Figure 6. The location of the New York City 03 plume is clearly
identified by the isopleths of surface 03 measurements. The analysis indicates
a rapid rise in 03 between 1000 EST and 1100 EST along a 75 km wide band from
the downwind edge of New York City across Long Island Sound and coastal
Connecticut. By 1400 EST the plume extended into Rhode Island with the highest
concentrations at ~100 km downwind of New York City. During the next several
hours the area of high ozone within the plume progressed northeastward toward the
Boston area. The highest concentrations at the surface decreased rapidly between
1600 EST and 1800 EST, but then remained fairly stable at -140 ppb through
2200 EST. On this day, transport appears to have been responsible for the maximum
03 concentration measured in the Boston area (154 ppb/2100 EST at Medfield, MA).
40
-------
-------
Tf* Trio*
LWDITUX:
Figure 6 (continued). Surface ozone concentration isopleths (ppb),
0800 through 2200 EST, on June 24, 1980.
42
-------
4.3 Temporal Changes in Ozone Above the Boundary Layer
The purpose of this task was to address the following question:
To what extent do 03 concentrations aloft increase between sunrise and mid-
morning when 03 aloft is entrained rapidly into the boundary layer during
the dissipation of the nocturnal inversion?
Daytime 03 concentrations within the boundary layer occur due to a
combination of physical and chemical processes, including photochemical
production, scavenging, transport, and entrainment from aloft. One of the
key parameters for modeling boundary layer 03 is the magnitude of 03 aloft
available for entrainment as the boundary layer grows in response to daytime
thermal convection. In many cases, a lack of extensive measurements requires
that assumptions be made regarding the temporal behavior of 03 entrained into
the boundary layer. It was the purpose of this task to investigate the tem-
poral variation in 03 concentrations aloft outside the boundary layer. Of
interest was whether substantial production of 03 aloft occurs during the day,
as a result of reactions among transported 03 and aged precursors. Because
the monitoring program did not include experiments to specifically address
this issue, the following analysis is restricted to using measurements obtained
for other purposes. As a result, only a cursory investigation of this topic
is possible, given the available data.
The analysis procedure was designed to identify groups of aircraft
spirals which represent quasi-Lagrangian measurements aloft during the day.
The temporal variation of 03 aloft on a particular day was determined by com-
paring measurements from these selected spirals. Evaluating 03 concentrations
43
-------
in a quasi-Lagrangian manner, rather than comparing time changes in
concentrations at a particular location, avoids the complicating influence
of variations in 03 aloft due to changes in transport.
All selected groups of spirals containing quasi-Lagrangian measurements
in an air parcel were pairs of early morning (0500/0600 EST) upwind and mid-
morning (0900/1000 EST) downwind spirals in Boston. For the spirals in each
group, temperature, dew point temerature, 03, bscat, and NOX measurements
were used in defining the vertical bounds of specific layers which were iso-
lated from the boundary layer during all spirals in the group. In most cases,
the spirals resembled one of the six characteristic profile types identified
by Ludwig ^ and shown in Figure 7. For types "a" and "b," 0^ concentra-
tions were averaged from above the layer of depletion near the surface to
the top of the spiral or an upper level inversion. For types "c" and "d," 03
concentrations were averaged vertically, beginning above the large gradient at
the top of the boundary layer to the top of the spiral or an upper level inver-
sion. For types "e" and "f" (and other patterns with large 03 gradients well
above the boundary layer), the spirals were divided into several layers and
the 03 data averaged for each layer separately. The transition zones of large
03 gradient were excluded from layer averages. In most cases, vertical bounds
of the selected layers were associated with changes in the atmospheric stabil-
ity. Discontinuities in the temperature/dew point temperature profiles which
marked a change in stability were usually identifiable on successive spirals
so that continuity of the layers was preserved. However, in some cases, the
top of the spiral had to be used as the upper bounds for computing vertical
averages when no stability discontinuity or pollutant gradient was observed
near the maximum altitude of the spiral. Tracking 03 concentrations within
44
-------
3
2
1
E
.*
1 0
1- (
X
o _
3
iu »
X
2
1
n
r i
1 a.
1
1
i
1
I
1
j
ii/ii
) 40 80 C
b.
_
;
^K-X| 1 1
-
C.
.
mmmzmmmm
?. MIXED LAYER YXX XX
XiXviXYXivXv^v/xiXYXi^XiXvX:!
) 40 80 120
9
\ d°
1
vivi-i^vi-x-Xvivi-x-x-x-:-:-:-:-:-:-:-:-::!:-:-:-:-:-:-
'£. MJ.X. E P. . L A Y E R . xJXxX::;
x-x-:i-x-x-iix-x-:fx-x-t:-:v:4xii?:iv:-:vi
e.
1
'£&*f???-:-SJ ABLE LA YE R
40 80 120 160
f.
XMIXEDX.
:::ii:::::::::i:x:;:::i^:
40 80 0 40 80 120 0 40
OZONE CONCENTRATION - ppb
1
80 120 160
Figure 7. Characteristic ozone profile types identified by Ludwig.
11
45
-------
'J i .(. r<-Uj, fairly homogeneous layers defined by stability discontinuities
minimized the probability that other processes, such as vertical dilution and
entrainment from the boundary layer, significantly affected 03 concentrations
aloft. Thus, any changes are most likely due to photochemical processes among
the pollutants aloft.
As a result of following the above procedures, thirteen cases were
identified for evaluating the formation of 63 aloft above the boundary layer.
The dates, times, dimensions, and 03 concentrations in these layers are pro-
vided in Table 11. Also provided are the profile type, and the observed
change in layer average 03 (residual). It is evident from the data that the
analyses included a wide range in initial 03 concentrations (?6 to 99 ppb).
Yet, only four cases (I, III, IV, and XI) stand out as having a measurable
increase in 03 concentration. In the remaining cases, 63 varied by H^ 5 ppb
or less, which was within +_ 10% of the initial concentration. Variations in
this range could be due to uncertainties in the measurement system, rather
than real fluctuations in 63 concentration.
In order to investigate why 03 increased in certain cases but remained
unchanged in others, NOX data were examined to see if the layers with appar-
ent 03 formation had higher NOX levels. Although no NMOC measurements were
available, bscat data and back trajectories were used to infer whether the
layers may have received precursors from major anthropogenic source areas
during the previous two days. In addition, observations of sky cover and
temperature were examined from the Boston National Weather Service station
to determine whether local meteorological conditions may have hindered or
enhanced 03 formation. However, neither variations in temperature nor cloud
cover could not explain the differences in 03 concentrations aloft.
46
-------
Table 11. Temporal Variations in Ozone Aloft
City:
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
Date
Boston
7/15/80
7/16/80
8/1/80
8/8/80
8/14/80
7/15/80
7/16/80
7/17/80
7/24/80
7/25/80
8/1/80
Time,
EST
0545
0915
0600
0945
0500
0930
0530
0945
0530
0850
0545
0915
0600
0945
0600
0945
0530
0930
0530
0930
0500
0930
Flight/
Spiral #
4-1
5-1
7-1
8-1
26-1
27-3
33-1
34-1
39-1
40-1
4-1
5-1
7-1
8-1
10-1
11-1
16-1
17-1
19-1
20-1
26-1
27-3
03 Profile Dimension of
Type Layer, m
(Ludwig) Bottom Top
e
e
b
c
e
f
b
c
b
a
e
e
b
c
b
a
a
a
b
a
e
f
Lower Layers
485
500
600
600
300
450
450
450
650
650
Upper Layers
1700
1660
1850
1840
1000
1000
1000
1000
1300
1300
1100
1170
1600
1500
1500
1500
800
800
1350
1350
1500
1500
2040
2050
2120
2100
1400
1400
2000
2000
1900
1900
1500
1520
03 Concentration (ppb)
Layer 403 of Layer
Average Peak Average
094
111
093
095
086
124
071
092
039
036
068
067
078
076
079
081
026
024
046
043
048
062
109
124
101
102
105
141
078
095
044
041
072
071
079
078
081
086
032
033
048
045
050
064
-K)17
+00 2
+038
+021
-003
-001
+002
+002
-002
-003
+014
-------
Examination of the NOX data indicates that the four comparisons (Cases I,
III, IV, and XI) in which 03 increased had higher NOX concentrations and bscat
than the other cases. Also, these four cases were associated with trajectories
that either had traveled along the Corridor or across portions of the Midwest
within 48 hours prior to reaching Boston. The largest residual ( + 38 ppb;
Case III) occurred in a layer which the trajectories and surface 63 data indi-
cate contained the remains of the New York City plume from the previous day.
The concentration of NOX (mostly NC^) was 20 ppb and b$cat was 2.18 x 103 nf1
within this layer. In Case IV, NOX and bscat were also comparatively high
(10 ppb and 2.0-3.00 x 103 nrl, respectively). The 48-hour trajectory path
from northern Indiana and Ohio, eastward across Massachusetts, suggests a
contribution from the upper Midwest to pollutant levels aloft. In Case I, the
layer had arrived in the Boston area after passing along the Corridor, but to
the west of New York City, NOX was 7 to 8 ppb and bscat was 1.00 x 103 nT1.
In the final case with an increase in 03 (Case XI), 03 was initially fairly
low (48 ppb), and bscat was also low at 1.00 x 103 m"*. However, the NOX con-
centration was relatively high at 14 ppb. The trajectories indicate that this
layer had been part of the daytime bounday layer over central and eastern
New York State the day before.
Of the seven cases with no change in 03, all had NOX levels of 7 ppb or
less, with an average concentration of 4 ppb. Except for Case II, the mag-
nitude of bscat was less than 1.00 x 103 m~* and averaged 0.51 x 103 m"*,
indicating that the aerosol content tended to be much lower than in the cases
when 03 increased.
The results of this analysis indicate that 03 production aloft was
apparent in those layers containing comparatively high air mass concentrations
48
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of NOX and perhaps other 03 precursors (as indicated by the aerosol content
and history of the layer relative to urban areas). It is likely that these
layers were within the daytime boundary layer on preceding days and, thus,
include the by-products of photochemical processes from boundary layer emis-
sions. However, 63 levels were fairly stable from sunrise through mid-morning
in cases in which NOX was comparatively low, and trajectories did not indicate
transport across areas of major anthropogenic emissions within 24 to 48 hours.
4.4 Comparison of Ozone Levels at the Surface and Aloft
The purpose of this task is to address two questions:
1. Do mid-morning surface 03 concentrations during the dissipation of
the nocturnal inversion reflect average 63 concentrations aloft prior to
mixing? That is, can mid-morning surface 03 measurements be used to estimate
overnight 03 transport aloft?
2. How well do afternoon 03 concentrations aloft compare with surface
03 concentrations at nearby stations? That is, can aircraft measurements be
used to infer surface 63 concentrations in areas without 63 monitoring sites?
Analyses conducted in the previous tasks indicate that a reservoir of air
with elevated 03 concentrations exists above the nocturnal inversion during
many nights. This layer of 03 has been separated by the inversion layer from
deposition at the surface and chemical scavenging by pollutants emitted near
the surface. Also, air in the layer containing elevated 03 aloft is subject
to transport over long distances overnight by winds above the inversion layer.
As the mixing height rises in the morning, due to surface heating, the 03 aloft
is entrained into the boundary layer and contributes to concentrations at the
surface.
49
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4.4.1 Comparison of Morning 03 Concentrations at the Surface and Aloft
In order to compare early morning levels of 03 aloft with surface
concentrations after inversion breakup, aircraft and surface 03 data were
tabulated for the New York and Boston areas as shown in Table 12. The table
contains three main sections. The first section containing five columns, pro-
vides the date, spiral number, time, layer thickness, and average 63 concentra-
tion aloft. The second section of three columns lists the three-hour average
surface 03 concentration, centered around the estimated time of inversion
breakup, for ground stations near the spiral site. The final three columns
list the time of inversion breakup, the 03 concentration aloft after inversion
breakup, and the time of these measurements. The inversion breakup time was
determined from sodar data and/or vertical temperature profiles. On days
when such data were unavailable, the median time of inversion breakup of 0930
EST was used.
All of the aircraft and surface data were taken from upwind
locations in order to avoid the confounding effects of 03 formation in the
urban plume. The early morning average 03 concentrations aloft were computed
for the layer above the surface layer and below 1500m (1500m was used as an
approximation for the upper limit of mixing during late morning). The late
morning 03 levels aloft in the New York area Were obtained upwind of the city,
shortly after the aircraft departed for the afternoon flight. In Boston, the
late morning data are layer averages through the boundary layer obtained from
spirals upwind at the completion of the mid-morning flight. Two of the
Boston study days, August 5 and 6, were not included in this task. August 5
was excluded because surface monitoring sites in the vicinity of aircraft
50
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Table 12. Comparison Of Mid-morning Surface Ozone With Early Morning Ozone Aloft
Early Homing 03 Aloft
Mid-morning Surface 03
1
Spiral
Date Number
1 1
Time, Altitude, 03, 03. Averaging3
EST Meters, HSL ppb ppb Time, EST
Time of Late
Inversion Morning
Location Dissipation, EST 03 aloft Time
New York Area
I 7/16/80 1
II 7/18/80 1
III 7/21/80 1
IV 7/22/80 1
V 7/24/80 1
VI 7/31/80 1
VII 8/6/80 1
VIII 8/8/80 1
0700 600-1500 085 082
073 0900-1100
087
0545 400-1500 119 062
069 0900-1100
0545 500-1500 076 079
114 0900-1100
110
0530 650-1500 056 051
053 0800-1000
053
0530 400-1500 035 037 0800-1000
042
0545 400-1500 060 059 0800-1000
059
0530 400-1500 071 069
076 1000-1200
061
0530 400-1500 067 097
107 1000-1200
088
Boston Area
Fleming ton
Marlboro 1000
Chester
Flemington
Chester 1000
Flemington
Marlboro 1000
Chester
Flemington
Marlboro 0900
Chester
Flemington 0900
Chester
Flemington 0830
Chester
Flemington
Marlboro 1030
Chester
Flemington
Marlboro 1030
Chester
-
065-070 1130
-
065-070 1130
045 1200
075-085 1130
065-075 1130
090-100 1130
IX 7/15/80 1 0545 485-1500 095 103 1000-1200 Easton
104 Attleboro
100
Sudbury
X 7/16/80 1 0600 600-1500 093 105 1000-1200 Easton
088 Medfleld
084
Sudbury
XI 7/17/80 1 0600 500-1500 079 073 0900-1100 Easton
057 Medfleld
054
Sudbury
XII 7/25/80 1 0530 500-1500 049 054 0800-1000 Medfleld
050 Attleboro
045 Sudbury
XIII 7/31/80 1 0530 500-1500 048 050 0900-1100 Hedfield
048 Easton
051 Georgetown
XIV 8/1/80 1 0500 200-1500 067 100 0900-1100 Easton
131 Medfield
098
Sudbury
XV 8/8/80 1 0530 450-1500 071
0900-1100 Easton
087 Medfleld
082 Worcester
1030
1100
0930
0900
1000
1000
1000
108
105
071
040
038
086
1015
1100
1045
1030
1030
105-115 1000
1100
aStart time of first hour and of last hour In averaging period.
51
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spirals were downwind of Boston as a result of the low level easterly wind
flow. August 6 was excluded because there were no early morning aircraft
flights on this day. These days were replaced by July 25 and 31 in this task
only.
In order to evaluate the use of surface 03 as an estimate of 03
aloft, values of residuals were computed by subtracting the surface 03 concen-
trations at each site from the respective concentrations aloft. The results
indicate a wide variation in "agreement," ranging from exact correspondence
to a 57 ppb underestimation of 03 aloft. To provide a clearer interpretation
of the residuals, the data set was separated into two groups. The first group
contains the ten cases in which surface 63 levels were somewhat homogeneous
(within +_ 15 ppb) among the upwind sites at the time of inversion breakup
(Cases I, II, IV, V, VI, VII, IX, XII, XIII, XV). The second group contains
the remaining five cases in which there were relatively large variations in
the upwind surface 63 levels (Cases III, VIII, X, XI, XIV). Such inhomoge-
neities in 03 may be attributable to spatial variations in: (1) 03 aloft;
(2) the time of inversion breakup; (3) the strength of vertical mixing; and
(4) 03 formation in the boundary layer.
Focusing on the first group indicates that, except for Case II,
average upwind surface 63 concentration at the time of inversion breakup
provides a reasonable estimate of 03 aloft some three to five hours earlier.
Excluding Case II, the average residual (sign ignored), for this group was
only 4 ppb indicating good agreement.
In the second group, the average absolute residual values were
fairly large (~30 ppb), excluding Case X. An explanation for the large
residuals in two of these cases (VIII and XIV) is evident from examining the
52
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late morning 03 measurements aloft. In both cases, 03 levels aloft had
actually increased substantially during the morning. As seen from the data
in Table 12, surface concentrations at the time of inversion breakup are
consistent with the later values aloft. That is, in these cases, the rela-
tively large residuals were apparently not due to the inability of average
surface concentrations to reflect 63 concentrations aloft, but rather to a
change in the upwind 03 concentration aloft between the time of the aircraft
measurement and the dissipation of the nocturnal inversion.
The large residual values and the difference in surface
concentrations in Case XI may be due to the presence of a low level subsi-
dence inversion (600m) which restricted vertical mixing after the dissipation
of the nocturnal inversion over portions of the Boston area. In both Case X
and XII, the 03 concentration at 1300 EST had increased to within a few ppb
of the concentration aloft, indicating that the reason for the difference in
03 observed earlier may have been due to a spatial variation in the time of
inversion breakup. For Case III, no late morning aircraft data are available,
so it is uncertain whether or not the relatively high surface 03 concentration
at the time of inversion breakup might be the result of an increase in 03 aloft.
Of the 15 cases examined in this task, 12 exhibited close
agreement between early morning 03 aloft and surface 03 concentrations during
the period of inversion breakup. In two of these 12 cases, upwind 03 aloft
changed substantially during the 3 to 5 hours between the initial aircraft
measurements and the time of inversion breakup. Thus, mid-morning surface 03
measurements appear to provide a useful estimate of early morning 03 aloft,
although care must be taken in using mid-morning 03 data for this purpose,
53
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particularly for cities such as New York City and Boston where urban areas are
less than a hundred kilometers apart and fluctuations in interurban transport
of 03 and precursors can be substantial between early morning and the time of
inversion breakup.
4.4.2 Comparison of Afternoon 03 Concentrations at the Surface and Aloft
The second aspect of this task concerns comparison of afternoon
03 concentrations at the surface and aloft. Of interest is whether 03 con-
centrations measured aloft by instrumented aircraft accurately represent the
concentrations at the surface. To examine this hypothesis, 03 concentrations
aloft from afternoon flights in the study region were compared with concen-
trations measured at nearby surface stations. Note that the aircraft meas-
urements used in these comparisons are 20-second average values, while the
surface data are hourly averages. In this analysis, pairs of measurements at
the surface and aloft were obtained for situations when the aircraft passed
within 15 km of a surface 03 monitoring site. The data for these comparisons
are given in Table 13 for the New York area and Table 14 for Boston.
The data indicate that large differences exist in many of the
comparisons. However, several explanations exist for the observed discrepan-
cies. As noted, the surface data are hourly averages, while the aircraft
data are instantaneous values. This difference in averaging times can in-
fluence the comparison. Another important factor is the large concentration
gradient which exists near the edge of an urban plume. In a number of cases,
as indicated in Tables 13 and 14, comparisons were made near the edge of the
plume, where sharp concentration gradients were observed. In this region,
small vertical or horizontal separations between the surface site and the
measurement point aloft can lead to large differences in 03 concentration.
54
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Table 13. Comparison of Afternoon Ozone Concentrations at
the Surface and Aloft in the New York Area
Date
7/18/80
7/22/80
7/24/80
7/31/80
8//6/80
8/8/80
03 Aloft
Tile 03
(EST) (ppb)
1126
1143
1253
1430
1551
1558
1805
1812
1814
1132
1142
1144
1205
1212
1316
1324
1359
1427
1431
1617
1654
1701
1743
1753
1759
1202
1211
1509
1522
1525
1142
1148
1203
1208
1229
1309
1318
1407
1721
1743
1755
1800
1809
1815
1155
1223
1248
1255
1302
1309
1451
1526
1549
1152
1213
1218
1222
1245
1251
1303
064
108
105
120
074
059
100
088
083
077
072
078
114
115
099
150
167
176
179
148
161
213
126
079
083
049
041
060
046
047
065
070
108
112
114
070
069
164
082
077
072
070
079
097
071
201
100
162
208
170
152
208
072
104
146
123
164
115
122
170
Surface 03
Time
(EST)
1100
1100
1200
1400
1500
1500
1800
1800
1800
1100
1100
1100
1200
1200
1300
1300
1300
1400
1400
1600
1600
1700
1700
1700
1700
1200
1200
1500
1500
1500
1100
1100
1200
1200
1200
1300
1300
1400
1700
1700
1700
1800
1800
1800
1100
1200
1200
1200
1300
1300
1400
1500
1500
1100
1200
1200
1200
1200
1200
1300
03
(ppb)
074
097
093
070»
068
059
078b
068b
043b
058
090C
127C
118
072d
087
174
213d
226d
092d
060 d
076d
111
125
123C
087
048
048
065
049
040
084
090
100
0708
070»
059
070
US*
070
070
101d
049b
034b
054b
085
171
090
180
249
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Table 14. Comparison of Afternoon Ozone Concentrations at the Surface and
Aloft 1n the Boston Area
Surface 03
Date
Time
(EST)
(ppb)
03
(ppb)
Time
(EST)
Station
Distance from
Surface Station, km
7/15/80
7/16/80
7/17/80
1525
1653
1639
1707
153
159
134
125
128
093
110
116
1500
1600
1600
1700
Medfield, MA
Medfield, MA
Medfield. MA
Medfield, MA (124 at 1800)
6.3
9.2
5.9
2.6
8/1/80
8/5/80
8/6/80
8/8/80
1357
1420
1423
1424
1432
1600
1355
1621
1657
1700
1704
1704
1707
1315
1326
1332
1538
1611
1516
1551
1555
126
125
128
130
108
151
133
104
125
107
105
105
107
089
101
098
074b
077b
090
076
082
117
112
114
117
113
098
096
100
105
116
100
042
060
111
106
089
075
068
067
075
064
13003
1400*
14003
1400«
1400
1500*
1400a
1600
1600
1700
1700
17003
1700*
1300
1300
1300
1500
1600
1500
1500
1500
Hamilton, MA (134 at 1200)
Hamilton, MA
Danvers. MA (130 at 1300)
Georgetown, MA (134 at 1300)
Manchester, NH
Portsmouth, NH
Georgetown, MA
Worcester, MA
Easton, MA (090 at 1700)
Medfield, MA (109 at 1600)
Sudbury, MA
Water town, MA
Somervllle, MA
Sudbury, MA
Medfield, MA
Quincy, MA
Easton, MA
Tewksbury, MA
Danvers, MA
Sudbury, MA
Tewksbury, MA
11.5
3.9
4.8
8.5
15.3
13.6
1.4
1.9
12.3
7.1
13.5
3.3
8,4
8.0
4.8
a Sea breeze or complex surface flow resulted In large vertical/horizontal gradients in Oj.
b Aircraft In region of large spatial gradient aloft; average concentration as aircraft passed the site.
56
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Comparisons made near coastal areas during a sea breeze flow were likely
influenced by the presence of a shallow internal bounday layer, which iso-
lated surface sites from the impact of a plume aloft, or prevented high
surface concentrations from mixing upward. In some of the the Boston cases,
vertical wind speed shear may have resulted in a faster travel time for
upwind transport aloft, such that the surface impact was an hour or so later
than that measured by the aircraft. Also, in comparisons of measurements made
late in the day (generally after 1700 or 1800 EST), surface concentrations
may have been depleted by local scavenging as the nocturnal stable layer
began to form and isolate 03 in the surface layer from 03 aloft. The cases
where these phenomena affect the surface/aloft comparisons are noted in Tables
13 and 14.
Considering the above factors, the 85 cases in the tables were
divided into two groups for the evaluation. Group I contains those cases
where the atmosphere is likely to be well mixed, and both measurements (sur-
face and aloft) were not on the fringe of the urban plume. Group II contains
those cases in which complicating features, as described above, were observed.
For Group I - New York (35 cases), the average residual (sign ignored) between
surface and aloft was 10 ppb. In 63 percent of the Group I cases, 03 aloft
exceeded 03 at the surface. In contrast, the average residual for Group II -
New York (25 cases) was 49 ppb. In most of the Group II cases 03 was much
higher aloft, due to depletion near the surface or as a result of low surface
concentrations in the sea breeze onshore flow.
For Group I - Boston (17 cases), the average residual of 15 ppb
was somewhat higher than in New York and, again, 03 aloft exceeded surface
57
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concentrations in most (71 percent) of the cases. In Group II - Boston (8
cases), the average residual was double the value of Group I.
One conclusion which can be drawn from these comparisons is that
aircraft data are most useful for estimating surface concentrations during
mid-day when the boundary layer tends to be well mixed, and in areas away
from the gradients associated with urban plumes and sea breeze flows. How-
ever, in some monitoring circumstances, the existence of such gradients will
not be known a priori , and their influence will be difficult to avoid. As a
consequence, the use of aircraft data to estimate fixed point surface 03
concentrations must be viewed with caution in the following situations:
(1) in areas with complex wind flow patterns- (2) in the vicinity of an urban
plume; and (3) when the column of air from the surface to the height of the
aircraft measurement is not well mixed. On the other hand, aircraft measure-
ments appear to be valuable for estimating surface 03 concentrations in the
absence of these cdmplicating situations.
58
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SECTION 5
CONCLUSIONS
It was the purpose of this study to investigate various aspects of ozone
formation and transport in the New York City and Boston portions of the
Northeast Corridor. At the outset of the study eight questions were posed
relative to this topic which were addressed through numerous analyses.
The conclusions of the study pertinent to these questions are presented
below.
1. Do concentrations of 03 and precursors transported into New
York City and Boston differ during along-Corridor and non-
Corridor transport regimes?
For New York City, morning precursor concentrations transported into the
urban area at the surface were twice as high with along-Corridor transport
than when transport was from outside the Corridor. Aloft, precursor concen-
tratins, particularly NMOC, were also much higher when transport was along the
Corridor. The analysis indicates that high morning precursor concentrations
transported into the New York area with along-Corridor flow were attributable
to overnight emissions in the Philadelphia area. During mid-afternoon the
impact of the Philadelphia 03 plume was typically observed at one or more
monitoring sites on the upwind (southwest) fringe of New York City.
In Boston, there was little difference in surface precursor concentrations
during along-Corridor versus non-Corridor transport regimes. However, the con-
centration of NMOC aloft during along-Corridor transport was triple the magni-
tude of aloft concentrations when transport was from outside the Corridor.
Average 03 aloft transported into Boston during the morning was also higher
with a long-corridor flow (100 ppb versus 76 ppb). The impact of the New York
59
-------
u>/ o. plunu- on portions of the Boston area was observed during the evening
across the upwind (southwest) fringe of Boston on days when transport was along
the Corridor.
The analyses indicate that the concentration of 03 and precursors trans-
ported into New York City and Boston can vary substantially depending upon
transport direction. Vertical variations in transort direction overnight were
often associated with large gradients in morning pollutant concentrations aloft.
Also, on occasion, transport of high 03 concentrations from major upwind cities
resulted in 63 exceeding the NAAQS in portions of the Boston and New York areas.
2. What is the diurnal variation of 63 and precursors in the air parcels
leading to the maximum 63 concentration in the urban plume?
In New York City, the concentration of 03 decreased as the air parcel
traveled from upwind rural and suburban locations into the urban area in the
morning, then increased rapidly later in the .morning as the air parcel departed
the city and the rate of photochemical reactions increased. In almost every
case, the maximum 0.3 concentration in the plume occurred between 1300 and
1500 EST. The concentrations of NO, N02, and NMOC generally peaked as the
air parcel crossed the city in the morning. The diurnal varition of 03 and
precursor concentrations are provided for 10 days in Section 4.1.2.
3. What is the average transport time and distance to maximum
03 in the urban plume? What is the typical downwind distance
to maximum N02 in the urban plume?
For New York City, the analyses indicate that the highest 03 concentrations
were associated with air parcels crossing the city at approximately 0800 EST.
On the average, air parcels crossing the city at 0800 EST generated an 03
maximum of 219 ppb at 1400 EST. The average downwind distance to maximum 03
was ~100 km. The average transport time to peak 03 was 5 to 7 hours.
60
-------
In the Boston area, aircraft data provided the most useful information
relative to these questions since the urban plume was transported over the
ocean on all but one case study day. The aircraft data indicate that the
average distance to the 03 maximum aloft was 81 km, with a range of 61 to
107 km. The average transport time to peak 03 was 4 hours.
At the surface, maximum N02 concentrations occurred in and immediately
downwind of the city. Aloft, away from the effect of local sources, maximum
midday N02 concentrations were measured 23 to 48 km downwind of New York
City, and 34 to 110 km downwind of Boston. For both cities, the transport
time to maximum N02 ranged from 1 to 3 hours.
4. What is the typical downwind distance to where NOX in the urban
plume becomes indistinguishable from background concentrations?
For three days in Boston and two days in New York City, the distance from
the urban area to the point where the urban plume NOX concentrations aloft be-
came indistinguishable from the air mass background NOX concentrations were
estimated. This distance ranged from 85 to 165 km. The estimated travel time
to background NOX ranged from 5.5 to 12 hours.
5. Can mid-morning surface 03 measurements be used to estimate early
morning upwind 03 aloft?
The analyses indicate that average upwind surface 03 concentrations (3
hour average centered around the time of inversion dissipation) do provide a
meaningful estimate of early morning 03 concentrations aloft in many cases.
However, there were also a number of cases when such an assumption would lead
to signficant underestimation (or overstimation) of the early morning levels
aloft. In these situations, it appears that 03 aloft transported into the
city had actually increased (or decreased) between the time of the early
61
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morning aircraft measurements and the time of inversion dissipation. This
may have been due to reactions among 63 and transported precursors or to
spatial variations in 03 aloft transported across the urban area. Thus,
using surface data for estimating early morning concentrations aloft should
be done with caution, particularly in situations where urban areas are in
fairly close proximity or high concentrations of transported precursors are
expected.
6. Can mid-day aircraft measurements of 03 be used to estimate
surface concentrations between measurement sites?
In locations where the atmosphere appears to be well mixed, surface and
aircraft data agree within 10 to 15 ppb. However, it was observed that strong
vertical and horizontal gradients confound the use of aircraft data for esti-
mating surface concentrations in the vicinity of urban plumes and sea breeze
ci rculations.
7. Does 03 aloft, initially isolated from the effects of surface
emissions and scavenging, change substantially prior to the
dissipation of the nocturanl inversion when pollutants aloft
are mixed to the surface?
The data examined indicate that, in most cases, 03 concentrations aloft
were fairly stable (within ±5 ppb) between early morning and mid-morning
measurements made within an air parcel. However, 03 production was evident
in those air parcels containing comparatively high air mass NOX concentra-
tions and probably other 03 precursors, as indicated by the aerosol content
ansd estimated track of the air parcel relative to upwind urban areas.
8. Is there evidence in the data of 03 plumes from medium size
cities such as Bridgeport, New Haven, and Hartford, CT or
Providence, RI?
In general, it was difficult to define 63 plumes from such cities due
to the relatively high air mass 63 levels, the complexity of airflow patterns
62
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and the frequent incursions of urban plumes from the major Corridor cities.
Also, since the monitoring program was not directed toward investigating these
cities, comparatively little data were available for this type of analysis.
However, on two occasions, there was evidence of the Providence 03 plume from
the Boston area aircraft data. In the clearest example, 03 in the Providence
plume was 20 to 30 ppb higher than the mass 03 concentration upwind, outside
the Boston plume.
63
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REFERENCES
1. Cleveland, W. S.; Kleiner, B.; McRae, J. E.; and Warner, J. L.,
"Photochemical Air Pollution: Transport from the New York City Area
into Connecticut and Massachusetts," Science, 191, 179 (1976).
2. Wolff, G. T.; Lioy, P. J.; Meyers, R. E.; Cederwall, R. T.; Wight, G. D.;
Pasceri, R. E.; and Taylor, R. S., "Anatomy of Two Ozone Transport
Episodes in the Washington, DC to Boston, Massacusetts Corridor," Environ.
Sci. and Tech., _U, 506 (1977).
3. Spicer, C. W.; Joseph, D. W.; Sticksel, P. R.; and Ward, G. F., "Ozone
Sources and Transport in the Northeastern United States," Environ. Sci.
and Tech., .13, 975 (1979).
4. Ludwig, F. L. and Shelar, E., "Ozone in the Northeastern United States,"
EPA-910/9-76-007, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina (1977).
5. Wolff, G. T.; Lioy, P. L.; Wight, G. D.; Meyers, R. E.; and
Cederwall, R. T., "An Investigation of Long-range Transport of Ozone
Across the Midwestern and Eastern United States," Atmos. Environ., 11,
797 (1977). ~
6. Reynolds, S. D. and Reid, L. E., "An Introduction to the SAI Airshed
Model and Its Usage," Systems Applications, Inc., Report EF 78-53R (1978).
7. Heffter, J. L.; Taylor, A. D.; and Ferber, G. J., "A Regional-Continental
Scale Transport, Diffusion and Deposition Model," NOAA Tech. Memo.
ERL ARL-50 (1975).
8. Heffter, J. L.; "Air Resources Laboratories Atmospheric Transport and
Dispersion Model (ARL-ATAD)," NOAA Tech. Memo. ERL ARL-81 (1980).
9. McNaughtpn, D. J. and Powell, D. C., RAPT--The Pacific Northwest
Laboratory Regional Air Pollutant Transport Model: A Guide," Report
prepared for the U.S. Department of Energy under contract DE-AC06-76RLO,
1830 (1981).
10. Spicer, C. W.; Joseph, D. W.; and Sticksel, P. R., "An Investigation of
the Ozone Plume from a Small City," J. Air Poll. Control Assoc., 32,
278 (1982).
11. Ludwig, F. L., "Assessment of Vertical Distributions of Photochemical
Pollutants and Meteorological Variables in the Vicinity of Urban Areas,"
EPA-450/4-79-017, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina (1979).
64
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/4-84-001
4. TITLE AND SUBTITLE
Northeast Corridor Regional
Precursor Transport in New
the 1980 Field Program
2. 3. RECIP
5. REPOf
Model inq Pro.iect Ozone and Augu
York City and Boston During 6-PERFC
7.AUTHOR c^ Poss1el) EpA. c> w_ Sp1cerj p> R; stickse'8'PERFC
and G. M. Sverdrup, BCL; and A. J. Alkezweeny and
W E Davic BNL
9. PERVOR'MING dRGANTlZATION NAME At
J.S. Environmental Protectic
Dffice of Air Quality Planni
Monitoring and Data Analysis
Research Triangle Park, NC
JO ADDRESS 10. PRO
)n Age!3cL , J A24A
ng and Standards n CON
Division (MD-14)
27711
12. SPONSORING AGENCY NAME AND ADDRESS 13. TYP
14. SPOf
15. SUPPLEMENTARY NOTES
lENT'S ACCESSION NO.
=IT DATE
St 1984
)RMING ORGANIZATION CODE
3RMING ORGANIZATION REPORT NO.
3RAM ELEMENT NO.
2F
TRACT/GRANT NO.
E OF REPORT AND PERIOD COVERED
MSORING AGENCY CODE
16. ABSTRACT
This report describes the results of a study to analyze portions of the Northeast
Corridor Regional Modeling Project (NECRMP) ambient data base collected in the New
York City and Boston urban areas. The study includes (1) an examination of the
ozone, oxides of nitrogen, and hydrocarbon concentrations transported into each city
and downwind in the urban plumes on 20 high ozone days; (2) the temporal changes in
ozone above the boundary layer; and (3) the relationship between surface ozone con-
centrations and mid-boundary layer values.
17.
a. DESCRIPTORS
Air Pollution
Ozone
Nitrogen Oxides
Hydrocarbons
Transport
18. DISTRIBUTION STATEMENT
KEY WORDS AND DOCUMENT ANALYSIS
b. IDENTIFIERS/OPEN END
NECRMP
New York City
Boston
Aircraft measurem
Urban plume
19. SECUHITY CLASS (This
20. SECURITY CLASS (This
ED TERMS c. COSATI Field/Group
ents
Report 1 21. NO. OF PAGES
80
pagei 22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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