United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
P.O Box 15027
Las Vegas NV 89114
EPA-600/4-79-037
USAF ESL-TR-79-33
July 1980
Research and Development
vvEPA
Williams Air Force
Base Air Quality
Monitoring
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximum interface in related fields. The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.This series
describes research conducted to develop new or improved methods and instrumentation
for the identification and quantification of environmental pollutants at the lowest
conceivably significant concentrations. It also includes studies to determine the ambient
concentrations of pollutants in the environment and/or the variance of pollutants as a
function of time or meteorological factors.
This document is available to the public through the National Technical Information
Service. Springfield, Virginia 22161
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EPA-600/4-80-037
July 1980
USAF: ESL-TR-79-33
WILLIAMS AIR FORCE BASE
AIR QUALITY MONITORING STUDY
by
D. C. Sheesley, S. J. Gordon and M. L. Ehlert
Northrop Services, Inc.
Environmental Sciences Center
Las Vegas, Nevada 89119
Contract No. 68-03-2591
Project Officer
J. L. Connolly
Monitoring Operations Division
Environmental Monitoring Systems Laboratory
Las Vegas, Nevada 89114
Prepared for
Department of the Air Force
Tyndall Air Force Base, Florida 32403
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring Systems
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
11
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FOREWORD
Protection of the environment requires effective regulatory actions
based on sound technical and scientific data. The data must include the
quantitative description and linking of pollutant sources, transport
mechanisms, interactions, and resulting effects on man and his environment.
Because of the complexities involved, assessment of exposure to specific
pollutants in the environment requires a total systems approach that
transcends the media of air, water, and land. The Environmental Monitoring
Systems Laboratory at Las Vegas contributes to the formation and enhancement
of a sound monitoring-data base for exposure assessment through programs
designed to:
develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment
demonstrate new monitoring systems and technologies
by applying them to fulfill special monitoring needs
of the Agency's operating programs
This report presents an evaluation of the impact of aircraft operations on
air quality at Williams Air Force Base near Phoenix, Arizona. The data
reported here will serve as input for defining the accuracy limits of the Air
Quality Assessment Model. This program was funded by the Department of the
Air Force, Department of the Navy and the U.S. Environmental Protection Agency
under an interagency agreement.
Director
Environmental Monitoring Systems Laboratory
Las Vegas, Nevada
iii
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SUMMARY
This report describes measurements made and data obtained during 13 months
of continuous air quality monitoring at Williams Air Force Base near Phoenix,
Arizona, during the period from June 1976 through June 1977. Air quality
parameters monitored from a network of five ground trailer stations included
carbon monoxide (CO), methane (City), total hydrocarbons (THC) measured as
methane, nitric oxide (NO), total nitrogen oxides (NOX), and coefficient of
light scattering (bscat). Meteorological parameters monitored included wind
speed and direction (WS and WDO, solar insolation, and (for three months only)
orthogonal wind components (u, v, and w) and mixing depth.
Data collection and analysis were oriented toward three primary
objectives:
1. The production of an air quality and meteorology data base for use in
defining accuracy limits for the Air Quality Assessment Model (AQAM)
formulation
2. The determination of the impact (if any) on Williams Air Force Base
(WAFB) air quality at ground level resulting from aircraft operations
3. The evaluation of results obtained from related special studies
designed to characterize horizontal and vertical dispersion of WAFB
emissions
Data recovery was determined to be approximately 70 percent for the 13-month
monitoring period. Based upon analysis of this data set, results indicate
that no significant air quality impact resulting from WAFB aircraft operations
was measured at any of the five ground stations. With the exception of
concentrations for CO and nonmethane hydrocarbons (NMHC, or hydrocarbons
corrected for methane), the data indicate only slight differences between
local airbase and background air quality concentrations. These differences
lie within the determined range of experimental measurement error.
Meteorological data indicate persistent diurnal windflow patterns, and
correlation of pollutant concentrations with windflow reveals that the main
sources of pollutants are indigenous to the airbase, thereby making feasible
the comparison between measured data and the AQAM predictions.
Results derived from related special studies conducted at WAFB suggest
that two or three categories of mixing height should be chosen in order to
evaluate AQAM performance, that jet plume rise and downwind horizontal
dispersion measurements are necessary in order to evaluate off-base air
quality impact, and that remote measurement techniques (although not
completely developed or standardized) may prove useful in the monitoring of
airbase air quality and dispersion of aircraft emissions.
iv
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Previous airport studies to evaluate models for prediction of air quality
impact suffered from the fact that nearby urban sources of pollutants masked
the airport emissions. Williams Air Force Base, Arizona, about 40 miles
southeast of Phoenix, was selected as an isolated, high-volume air traffic
facility to study airbase and aircraft emissions activity. Selection of
Williams enabled the monitoring of airbase emissions in an ambient environment
relatively free from nearby sources of pollutants that would interfere with
measurements made in the vicinity of airbase emissions.
Project planning was done by the U.S. Environmental Protection Agency,
U.S. Air Force (USAF), U.S. Navy and Argonne National Laboratories (ANL).
Planning included the siting and determination of numbers of stations to be
used, pollutant-sensor selection, and definition of aircraft operations to be
studied. Station siting also involved an evaluation of historical
meteorological data and the physical layout of the base. Monitoring stations
were located adjacent to aircraft operations to monitor queueing, departure,
and arrival of aircraft as well as related base sources of emissions. Two
stations were located in areas on the base that were expected to be least
impacted by local emissions, as anticipated during the study design. The
resulting five-station monitoring network was linked to a central recording
system for automatic data acquisition at one-minute intervals.
The instrumentation for continuous monitoring of air quality used in this
study was representative of the state of the art available in 1975 in terms of
second-generation instrument development and techniques for calibration and
operation.
The following instruments were selected based upon their availability and
on previous Environmental Monitoring Systems Laboratory (EMSL) experience:
Gas chromatograph with continuous flame ionization detector for THC,
City, and CO in the parts-per-billion (ppb) to parts-per-million (ppm)
concentration ranges, a wide linear range, and a self-calibration
feature
Dual-reaction-chamber chemiluminescent analyzer for NO and NOX in the
ppb concentration range
A nephelometer for light scattering in the visible wavelength (measured
scattering coefficient is then related to the visible range in the
atmosphere)
WS and WD propeller vane sensors located approximately 8 (meters) above
ground level (AGL)
The monitoring systems network was subjected to a daily routine of
inspections, calibration checks, and preventive maintenance. Additional
meteorological sensors were utilized during various phases of the study to
collect specific information relating to atmospheric stability and dispersion.
These sensors included a pyranometer, an acoustic sounder, orthogonal wind
component sensors, temperature differential probes, and boundary layer profile
sensors.
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Automatic data acquisition included the recording of continuous
measurements for oxides of nitrogen (NOX), methane (City), total
hydrocarbons (THC) measured as methane, carbon monoxide (CO), wind speed and
direction, and nephelometer scattering coefficient. Data were digitized,
recorded, and stored on magnetic tape. Four levels of data processing were
performed at both Williams AFB and EMSL in Las Vegas, Nevada. One-minute data
were converted to hourly averages and provided on tape to ANL to perform the
accuracy definition of AQAM under contract to the U.S. Air Force. Air quality
averages were compiled as tabular summaries and monthly plots of concentration
versus time.
Data processing activities for the WAFB project included the following
activities:
Handling one-minute data tapes acquired from the air monitoring network
and verifying the contents of these tapes
Calibrating the one-minute voltage tapes and converting the voltages to
engineering units
Averaging the one-minute data to produce hourly averages and
calculating the root mean square average, the standard deviation, and
the maximum and minimum for each hour
Coding, Williams Air Force Base Aerometric Network (WABAN)
meteorological data onto computer forms and tape cartridges and merging
these data into a data file of consistent format for each month that
air quality data were collected
Presenting data in the form of tabular listings of hourly data,
frequencies and cumulative frequencies of NO, CO, NMHC, and bscat
(nephelometer), cumulative frequency distribution plots of these four
parameters, time plots of the hourly averages, time plots of minute
values for four Julian days, and microfiche of the tabular listings
Compressing 395 one-minute data tapes onto a 20-reel set for use by ANL
in AQAM accuracy definition analysis
Digital voltage data from each of the five monitoring stations were
recorded at one-minute intervals on magnetic tape in the central data
acquisition facility (Building 16) at WAFB. Procedures were developed to
convert the one-minute air quality data to hourly averages. The
hourly-averaged data are presented in tabular summaries and monthly plots of
concentration versus time. The data set includes all continuous air quality
and meteorology data taken from the air monitoring network over a 13-month
period. Processing required several levels of interactive editing with the
use of control charts of zero, span, and calibration information to support
data correction and adjustment. Checks for internal consistency were
uniformly applied during data processing, and transmittal errors and rejected
data were identified. Data were accepted or rejected through editing,
verification, and screening based on a predetermined set of criteria. The
vi
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goal in processing was to assure that corrections were made for causes
documented in operations logbooks for each monitoring station of the network.
Meteorology data collected as hourly observations on WABAN forms were
coded by the USAF and provided on one magnetic tape. This tape also included
the acoustic sounder mixing depth information. Additional meteorology data
collected at monitoring station 4 from April to June 1977 are available on the
one-minute magnetic tapes collected in the central data acquisition facility-
Although the related special studies conducted at Williams Air Force Base
have provided insight into the general aspects of pollutant dispersion at
WAFB, current analyses of the results of these studies have not led to
specific conclusions with respect to WAFB emissions impact on base air
quality. Integrated long-path monitoring for CO and NOX shows promise of
providing~~viable techniques to describe dispersion at airbases. The amount of
aircraft emissions, combined with some long-path CO measurements taken
adjacent to taxiways, suggest that jet exhaust plumes rise quickly in the
vicinity of emissions. Micrometeorologicai studies to measure parameters
important for describing mixing depth and vertical and horizontal dispersion
suggest that significant improvement can be made to site-specific models used
to assess emissions impact at airbases. A single jet exhaust study using a
helicopter platform showed jet plumes at significant vertical height (47 m)
relatively close (200 m) to the point of emission.
Conclusions drawn from these studies are relevant as far as the assessment
of air quality at the five monitoring stations. Commercial monitoring
instrumentation has limits of detection that restrict its usefulness for the
collection of model input data at ground level in the vicinity of jet exhaust
emissions. An additional limitation at WAFB was caused by the immediate
vertical rise of exhaust emissions, placing pollutants at altitudes that are
not sampled by ground-based analyzers.
Twelve months of data were selected and averaged to provide an annual
basis for assessing air quality at the five monitoring sites. Ambient
concentrations of NOX, NMHC (hydrocarbon corrected for methane), and CO were
measured at and near the limits of detection for the continuous analyzers.
However, sufficient calibration and daily check data were maintained to allow
a determination of measurement precision and accuracy limits for the data set
collected.
Valid data were recovered for 70 percent of the 13-month monitoring
period, and the data base is representative of ambient air quality at WAFB in
the vicinity of the ground monitoring sites. On an annual average basis,
there is persistent evidence of emission sources, particularly in the case of
CO concentrations. The data indicate a measurable effect on air quality at
ground stations 2, 3, 4 and 5 as a result of aircraft operations. In
addition, the effect on air quality as measured at Station 4 is separate and
distinct from that at stations 2, 3 and 5 resulting from nonaircraft-related
base operations. However, neither of these measured effects is significant in
the context of the determined range of experimental measurement error.
Results of the related special studies also support this conclusion, although
the time period of investigation for these studies was considerably shorter.
vii
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In relation to the National Ambient Air Quality Standards (NAAQS), ambient
concentrations measured at WAFB did not at any time exceed the NAAQS for CO
and N02 (determined by the fact that NOX concentrations never exceeded the
NAAQS for N02>. Concentrations of NMHC exceeded the recommended 6:00 a.m.
to 9:00 a.m. guideline only at times other than 6:00 a.m. to 9:00 a.m.
The Williams AFB experimental study demonstrated conclusively that
aircraft and airbase emissions did not impact air quality significantly in the
vicinity of emissions that contribute the major pollutants (CO and HC).
Results of the related special studies and the continuous monitoring suggest
that dispersion of hot exhaust from aircraft occurs very quickly at WAFB, and
the typical WAFB meteorological condition affords a low potential for
exceeding the NAAQS.
The methods for acquiring data to define the accuracy of a model need
careful study in subsequent airport programs designed to develop models useful
for predicting impact on ambient air quality. The development of monitoring
systems to measure plumes above ground level was shown to be feasible, based
on limited studies at Williams AFB. Therefore, a carefully conceived
monitoring system consisting of appropriate emphasis on local meteorology,
elevated sampling, and limited ground monitoring is recommended for subsequent
studies of air pollution emissions at airbases.
Monitoring over long-path lines at ground level may also permit the
collection of data more consistent with model results. Monitoring objectives
to collect data in relation to NAAQS compliance should be considered as
separate and distinct from those for acquisition of model input data since the
monitoring technology required for each is different.
One significant result obtained from the WAFB study was the realization
that air quality impact cannot be effectively determined in areas where
emissions take place at elevated temperatures (aircraft exhaust) through the
use of ground sensors located in the vicinity of the emissions. Sensors must
be placed in locations where emissions are predicted to have maximum impact as
determined by study of historical meteorology and by intensive above-ground
measurements conducted to characterize pollutant transport away from the
emission sources (horizontally and vertically).
Statistical meteorological studies should be conducted for the Naval Air
Station (NAS) to provide specific information for site selection and
determination of the number of sites needed for both model data base input and
impact assessment. Station siting should also be dependent upon the number
and location of significant emission sources.
Micrometeorological data should be acquired in order to determine
horizontal and vertical dispersion parameters together with atmospheric
stability classifications. These data can be obtained by use of tethered
balloon platforms and boundary layer profile sensors. Above-ground air
quality measurements should be conducted from tower or airborne platforms to
quantify the vertical transport of emissions away from the study area. In
addition, horizontal pollutant dispersion should be measured during
representative meteorological conditions by making intensive measurements over
viii
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short time periods from a network of portable ground sensors. The latter is
particularly appropriate in terms of measuring particulate transport.
Emissions and their dispersion need not be monitored continuously for
extended periods of time if data are obtained during each representative
meteorological condition, unless the data collected prove to be inconclusive.
Ground sampling data must be acquired in the vicinity of known emissions (such
as hot refueling) and in locations some distance from known sources (for
example, off base or near airbase boundary) to determine changes in air
quality and to qualitatively measure pollutant transport.
Short-term intensive monitoring is also recommended in order to determine
the relationship between dispersion data and data from the fixed ground sites.
Airborne and balloon-borne sensors are effective in this approach, and these
data should be incorporated with local micrometeorology to make a
determination of local source contributions.
ix
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CONTENTS
Foreword ..... . ............. . ............ iii
Summary ................................. iv
Figures ................................. xii
Tables ...... , .......................... xiii
Abbreviations and Symbols ........................ xiv
1. Introduction .......................... 1
1.1 Background ....................... 1
1.2 Objectives of the study ................. 4
1.3 Geography and climatology of the Phoenix area ...... 5
2. Continuous Air Quality Monitoring Network ........... 8
2.1 Design and planning ................... 8
2.2 Short-term special study .............. . . 10
2.3 Continuous monitoring .................. 14
2.4 Additional meteorological instrumentation ........ 18
2.5 Monitoring operations .................. 19
2.6 Quality control ..................... 23
3. Data Processing ........................ 26
3.1 Air quality data .................... 27
3.2 Meteorology data .................... 28
3.3 Data summaries ..................... 30
4. Data Analysis and Evaluation .................. 31
4.1 Data recovery ...................... 31
4.2 Wind speed and direction instrument
performance ...................... 34
4.3 Performance of continuous air quality
analyzers ....................... 35
4.4 Representative meteorological conditions ........ 45
4.5 Observations based on annual averages .......... 49
4.6 Assessment of impact on air quality at the
monitoring sites ................... 55
4.7 Results of related special studies ........... 58
5. Conclusions and Recommendations ................ 64
5.1 Data base accuracy definition for AQAM ......... 65
5.2 Assessment of air quality impact at WAFB ........ 65
5.3 Related special studies ................. 67
5.4 Recommmendations for NAS Miramar studies ........ 70
References
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Page
Appendices*
A. Project organization and implementation A-l
B. Related special studies B-l
C. Measurement principles and performance specifications
for WAFB analyzers C-l
D. Calibration procedures for air quality monitoring
instrumentation D-l
E. Daily trailer inspection, zero and span checks, and
station calibration adjustments E-l
F. Coding for data switches (thumbwheels) of the data
links at monitoring stations F-l
G. Lists of secondary calibration gases and their locations
and dates of use at WAFB G-l
H. Hourly averages and time series plots of the data H-l
1. Data processing 1-1
J. Procedure for acoustic sounder data reduction J-l
K. Cumulative frequency distributions of air quality
parameters K-l
References for Appendices R-l
* The Appendixes are available from National Technical Information Center,
Springfield, VA 22161
xi
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FIGURES
Number Page
1 USAF/EPA program activities 3
2 Map of Arizona showing WAFB 4
3 WAFB wind rose for March 1942-July 1967 6
4 Map of WAFB showing monitoring site locations 9
5 Sampling grid of single jet study at WAFB 11
6 WAFB transmitter (site 1) CO pollution rose, May 1975 13
7 Block diagram of trailer instrumentation 17
8 Air quality intake system 17
9 Data collection system. 18
10 Calibration system for air quality trailers 25
11 Base meteorology data processing steps 29
12 October 1976 control chart for the Beckman 6800 analyzer
at station 3 41
13 April 1977 NO/NOX control chart for station 5 43
14 Annual wind rose at station 1, WAFB, from June 1976 to June 1977. . . 46
15 Annual wind rose at station 2, WAFB, from June 1976 to June 1977. . . 46
16 Annual wind rose at station 3, WAFB, from June 1976 to June 1977. . . 47
17 Annual wind rose at station 4, WAFB, from June 1976 to June 1977. . . 47
18 Annual wind rose at station 5, WAFB, from June 1976 to June 1977. . . 48
xii
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TABLES
Number Page
1 Average CO and THC Concentrations for Static Jet
Bag Samples 11
2 Summary of Highest Hourly Averages for THC, Ofy, and CO
during 1975 Short-Term Preliminary Study 14
3 Siting Criteria for Five Air Monitoring Trailers 15
4 Instrumentation Summary 20
5 Performance Specifications 22
6 Operaton and Calibration Schedule for Monitoring Network 23
7 Percent of Data Recovery for Five Monitoring Stations of
WAFB Study 32
8 Systems Downtime at Stations 2 and 3 33
9 Summary of Air Quality Parameters at WAFB 37
10 Wind Direction and Time of Day 49
11 12-month Geometric Mean Concentration and Geometric Standard
Deviation for WAFB 50
12 Station 1 Average Values for July 1976 through June 1977 51
13 Station 2 Average Values for July 1976 through June 1977 51
14 Station 3 Average Values for July 1976 through June 1977 52
15 Station 4 Average Values for July 1976 through June 1977 52
16 Station 5 Average Values for July 1976 through June 1977 53
17 Date and Time CO Exceeded 3 ppm 54
18 Annual Average Concentrations for All Stations,
July 1976 through June 1977 55
19 Annual Average Air Quality Concentrations at WAFB 56
20 Comparison of Selected Annual Average Concentrations 57
21 Comparison of Data from Stations 1 and 4 During East-Southest
Wind Conditions 57
xiii
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LIST OF ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
A ampere
AF Air Force
AFB Air Force base
AFCEC Air Force Civil Engineering Center, Kirkland AFB, New Mexico
AGL above ground level
ANL Argonne National Laboratory
AQAM Air Quality Assessment Model
AVAP Airport Vicinity Air Pollution Model
BDCS Bendix Dynamic Calibration System
Btu British thermal unit(s)
BPI bits per inch
CDC Control Data Corporation
CEEDO AF Civil and Environmental Engineering Office, Tyndall AFB,
Florida
COSPEC Barringer correlation spectrometer
DEC Washington National Airport
EMI Environmental Measurements, Inc.
EMSL-LV Environmental Monitoring Systems Laboratory, Las Vegas, Nevada
EPA U.S. Environmental Protection Agency
ERSL Environmental Research Support Laboratory, NSI, Research Triangle
Park, North Carolina
FAA Federal Aviation Administration
GFC gas-filtered correlation spectrometer
HP Hewlett-Packard Corporation
Hz hertz
IITRI Illinois Institute of Technology Research Institute
IRG interrecord gap
kw kilowatt
ML Monitor Labs Corporation
MOA Monitoring Operations Division, Air Quality Branch (EPA/EMSL-LV)
MRI Meteorology Research, Inc.
mV millivolt
NAAQS National Ambient Air Quality Standard
NBS National Bureau of Standards
NMHC nonmethane hydrocarbon
NOAA National Oceanic and Atmospheric Administration
NREC Northern Research and Engineering Corporation
NSI Northrop Services, Inc.
pibal pilot balloon
ppb parts per billion
ppm parts per million
ppmM parts per million - meters
xiv
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ROSE
rpm
SLDVS
THC
TS
TSP
USAF
UTM
V
WABAN
WAFB
WD
WS
SYMBOLS
S02
N2
CH4
CO
NO
NOX
03
a
AT/AZ
remote optical sensing of emissions system
revolutions per minute
scanning laser Doppler velocimeter system
total hydrocarbbons
total sulfur
total suspended particulates
United States Air Force
universal transverse mercator coordinates
volt or voltage
Williams Air Force Base Aerometric Network
Williams Air Force Base, Arizona
wind direction
wind speed
sulfur dioxide
nitrogen dioxide
hydrogen
nitrogen
methane
carbon monoxide
nitric oxide
oxides of nitrogen
ozone
sigma
theta
beta
changes in temperature with changes in height
xv
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SECTION 1
INTRODUCTION
The measurement and data acquisition techniques presented in this report
describe work performed under contract to the U.S. Environmental Protection
Agency, Environmental Monitoring Systems Laboratory, Las Vegas, Nevada
(EPA/EMSL-LV). During monitoring operations conducted from five ground
stations at Williams Air Force Base (WAFB) near Phoenix, Arizona, air quallity
data were collected for a 13-month period (June 1976 through June 1977). Data
from this experimental study are presented together with a preliminary
interpretation of the WAFB impact on local air quality. These data will also
be used by the U.S. Air Force (USAF) to define the accuracy limits of the Air
Quality Assessment Model (AQAM) under contract to Argonne National
Laboratories (ANL).
1.1 BACKGROUND
The current method of predicting the air quality impact resulting from
airport operations (both in their present and future configurations) uses a
properly validated air quality computer model. Few air quality models have
been developed specifically to calculate airport air quality impact [1-4]
because of the extremely detailed emissions input required. The function of
any such model is to account correctly for pollutant emissions into the
atmosphere and to describe and predict their subsequent dispersion. The
Gaussian dispersion formulation is widely used in airport models because it is
appropriate for the scale of distances (0-5 kilometers (km)) and short
pollutant travel times (0-3 hours (h)) associated with airport emissions.
Recent studies [5-9] have indicated that any air quality impact predicted by
these airport models will occur on a local scale (5 km radius or less).
Two Government-sponsored, steady-state Gaussian plume dispersion models
have been developed. The first model was developed under EPA contract by
Northern Research and Engineering Corporation (NREC) [1] and was later
modified by Geomet, Inc. [3], also under EPA contract, to improve its air
quality predictive capability. It is currently referred to as either the
"modified NREC model" or the "Geomet model." An attempt was made to compare
results of the Geomet model wifh data collected at Washington National Airport
(DCA) during the six-month period from October 1972 through April 1973.
Accuracy comparison was incomplete, however, because of the continued presence
of higher pollution levels from sources other than DCA aircraft (mostly
vehicular traffic associated with surrounding roads and highways), which
masked pollutant concentration variations resulting from airport sources.
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The second Government-sponsored airport model was developed by ANL under
contract to the USAF and the Federal Aviation Administration (FAA). This
effort produced two models. The first version, the Airport Vicinity Air
Pollution (AVAP) model [2], has a civilian aircraft and activity emissions
input routine. Limited evaluation has been attempted on AVAP; however, no
real conclusions could be drawn because of the limited amount of data
available. The second, AQAM [4], has a USAF emissions inventory refinement
that includes all military-type aircraft and base activities. The Gaussian
air pollution dispersion algorithm used is similar in both AVAP and AQAM. The
AQAM model has the capability of predicting annual concentrations, in addition
to short-term air quality calculations.
A study prepared for the FAA, "A Survey of Computer Models for Predicting
Air Pollution from Airports" [8], concluded that no evaluation of an airport
air pollution model had been performed to date. Previous attempts to collect
an adequate data base [1-3 and 8] were conducted at high traffic-volume
civilian airports located in areas of high background air pollution that
masked the effect of airport emissions.
Haber [8] also noted that "a controlled evaluation of the basic transport
and diffusion equations" should be conducted. A controlled evaluation is
particularly needed to verify current airport models that represent aircraft
emissions on runways as continuous line or point sources of pollution. These
formulations are based on dispersion data generated from experiments with
elevated point sources of emissions. Such line-source formulations should be
studied experimentally before the models receive widespread application in
environmental impact assessment.
Haber1s most important recommendation was that an accuracy definition
program should be conducted under controlled experimental conditions. Because
a controlled experiment would be nearly impossible at a civilian airport,
Haber suggested that the next best experimental site would be a relatively
remote, high traffic-volume, military airfield where accurate statistics would
be available for aircraft type, mix, and activity schedules from which
emissions input data are calculated. Requirements for accuracy definition are
shown in Figure 1. Note that meteorological data are required both for
comparison and model calculation.
Gaussian air quality models require model inputs for estimation of the
stability of the atmosphere throughout the mixed layer, where most pollution
is dispersed from moving and fixed sources. These inputs consist of
meteorological measurements of vertical temperature and mean wind profiles,
and vertical and horizontal wind variability with time. Air quality
measurement can be applied in this way to characterize concentration profiles
in three dimensions for comparison to model calculations. Remote sensing
methods also provide data that may show elevated concentrations above ground,
and integrated paths of concentration horizontal to the ground, for the
purpose of comparing predicted concentrations to actual measurements.
Model accuracy definition requires that daily, monthly, and seasonal
distributions of air quality and meteorological data be collected to evaluate
the AQAM. Frequency distributions of one-hour averages of air quality
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parameters are used to compare AQAM calculations to measured frequency
distributions (see Figure 1).
REVISIONS
(AND
MODEL
(AQAM)
MODEL ACCURACY DEFINITION
/COMPARE FREQUENCY\
\ DISTRIBUTIONS )
(AND
EMISSION
DATA
METEOROLOGY
DATA
1
AIR QUALITY
DATA
(SRI)
(WABANHANU (EPA/EMSL-LV)
(EPA/EMSL-LV)
(USAF)
Figure 1. USAF/EPA program activities.
In summary, the Air Force AQAM accuracy limits may be defined by
conducting the following activities:
Selecting a suitable airbase, free from interfering urban pollution.
Collecting an air quality and meteorology data base with a suitable
number of ground-level sites for the assessment of model accuracy in an
area of airbase emissions impact.
Comparing frequency distributions for model-calculated pollutant
concentrations to those for actual ground measurement data.
Williams Air Force Base, southeast of Phoenix, Arizona, and east of the
town of Chandler, Arizona (Figure 2), was selected as a high-volume air
traffic facility for a study of the impact on ambient air quality resulting
from aircraft emissions and other indirect sources of pollutants on the base.
Statistics were available for aircraft type, mix, and activity schedules at
WAFB. WAFB offered the following advantages for monitoring and model
evaluation: a large volume of aircraft traffic resulting in large estimated
emissions of carbon monoxide (CO) and total hydrocarbons (THC), and relatively
few local pollutant sources (resulting in low background levels), so that
greater resolution of the impact of air base operations could be determined
for model evaluation [10]. The emissions to be monitored for impact
assessment would be CO, THC, methane (Clfy), and nitrogen oxides (NOX) from
locations in the vicinity of WAFB activities over a statistically acceptable
period of time in order to obtain representative meteorological conditions.
-------
Figure 2. Map of Arizona showing WAFB.
1.2 OBJECTIVES OF THE STUDY
The USAF, the U.S. Navy, and the EPA share a common interest in
determining the impact of airport activities on local air quality and in
evaluating the AQAM model. They formed an interagency agreement (IAG-R5-0788)
in May 1975 with the following objectives:
To collect a data base of airport-related air quality measurements to
evaluate the Air Force AQAM model.
To determine the impact (if any) of airport-related activity on local
(5-km radius) air quality.
To conduct a series of special studies to provide information on
horizontal and vertical dispersion to supplement any model revision by
ANL.
The WAFB study addressed the first two objectives of the agreement by
collecting data at one-minute intervals from five fixed monitoring sites at
WAFB, converting the data to hourly averages and providing these hourly
averages to ANL. AQAM model accuracy is to be defined by using it to
-------
calculate one-hour average pollutant concentrations and then comparing them to
frequency distributions for data collected by the WAFB air monitoring network
from June 1976 through June 1977. Since meteorological and emissions data (as
well as air quality data) are needed in the Gaussian formulation of the AQAM
to calculate the one-hour frequency distributions (see Figure 1), daily
meteorological observations from the Williams Air Force Base Aerometric
Network (WABAN) were obtained during the monitoring period. Certain
meteorological data were also acquired at the fixed-site ground monitoring
locations.
An April 1975 feasibility study, performed at WAFB by the USAF, EPA, and
ANL, was used to determine the number of monitoring stations necessary for the
air monitoring network, the rationale for their location, and the suitability
of measurement techniques being applied in the experimental study.
Past airport monitoring studies have not measured concentrations
significantly above background levels [2, 8 and 9], possibly because the plume
rise is significant as hot buoyant gases exit the aircraft engines.
Meteorological conditions and runway surface temperature may also have a
significant effect on plume rise. Airport models do not normally evaluate
these features or incorporate terms for landing and takeoff cycles. Any
evaluation of an air quality model such as AQAM will require supporting
measurement data in order to define plume rise and meteorological parameters
not measured by the fixed ground monitoring network. Therefore, the third
objective of the interagency agreement required that additional studies be
conducted at WAFB. Vertical and horizontal dispersion at WAFB were
investigated during a portion of the EPA study period in order to augment the
fixed-point ground-level data.
Another special study related to this project generated data to explore
plume trajectories from the various indirect sources created by queuing and
idling aircraft [11]. Ground-based and airborne moving sampling platforms
were also used at WAFB to provide air pollution mapping. Correlation
spectrometer measurements to provide insight into plume trajectory, plume
rise, and points of maximum downwind concentrations were also made early in
the study to satisfy the monitoring requirements imposed by objective 3.
Summaries of these special studies are included in this report, and full
reports are available under separate cover as indicated.
1.3 GEOGRAPHY AND CLIMATOLOGY OF THE PHOENIX AREA
Williams Air Force Base is located at latitude 33°18' N and longitude
111°40' W, approximately 40 km southeast of Phoenix, Arizona, at 422 meters
(m) above sea level. This location is on the northeastern edge of a large
semiarid desert valley that extends westward to the California Coastal
Mountains and southward to the Gulf of California. For 16 km in every
direction from the base, the land is almost flat. The nearest mountains of
significance are the SanTans, 16 km to the south, and the Superstitions, 24 km
to the northeast (Figure 2). Westward from the base, the valley floor is
broken irregularly by small mountains and short mountain ranges. The nearest
of these mountain ranges is the Sierra Estrella Mountains, which rise sharply
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to more than 1,370 m above mean sea level. From the northwest clockwise
through the southeast, the terrain is mountainous with many peaks above
2,000 m. Except for irrigation canals, there are no significant water
features, and local air is characteristically dry.
The land to the east of the base is typical desert, covered with growths
of sagebrush, cactus, and mesquite. From the southeast clockwise through the
north, the land is irrigated, producing (in season) cotton, alfalfa, melons,
citrus, and many vegetables. Citrus fruit groves are numerous. The
Phoenix-Tempe-Mesa metropolitan area is expanding to the southeast toward
WAFB, gradually reducing the quantity of cultivated land. The majority of the
base is built on a rock and sand foundation with few trees and many lawns.
The airfield complex is covered by either concrete, asphalt, bituminous
matting, or gravel.
Windflows influenced the siting and planning of the air monitoring
network. A climatological wind rose derived from WAFB weather records for the
period from March 1942 to July 1967 (Figure 3) shows that the predominant wind
direction (WD) is from the east through the southeast [12], A secondary
direction is from the west through the northwest. The normal diurnal pattern
is for the winds to veer through 360 degrees daily. This directional pattern
NNW
WNW
ENE
WSW
ESE
SSW
SSE
CALM 26.7%
( velocity le« than 10 m/i 1
Figure 3. WAFB wind rose for March 1942-July 1967.
-------
of surface winds persists throughout the year. At night, the low-level air
cools as the result of radiative heat loss and tends to sink. This dense air
flows down the mountains and into the valleys, causing drainage winds. At
WAFB, flow is southeasterly from higher ground down towards the Salt River and
Phoenix. Typically, by late morning the radiation inversion has dissipated
and the mixed layer increases in depth. The low-level air, now less dense,
flows up the valley floor surfaces and can be forced up over the mountains.
This condition lasts well into the evening.
There are no dominant seasonal wind regimes comparable in magnitude to the
diurnal changes. The greatest frequency of winds over 5 meters per second
(m/s) occurs from April to July, and winds with speeds over 10 m/s are most
commonly associated with nearby thunderstorm or frontal activity.
-------
SECTION 2
CONTINUOUS AIR QUALITY MONITORING NETWORK
The WAFB monitoring network consisted of a central data acquisition
facility (located in Building 16) and five trailers utilized as fixed-site
monitoring stations (Figure 4). The central facility contained space for
recordkeeping, instrument repair and maintenance, and electronic data
processing. The monitoring network was composed of two subsystems
measurement sensors and data acquisition. Data acquisition included the
measurements collected by continuous air qjuality and meteorology monitoring
instruments. These measurements were recorded as digitized data on magnetic
tape. Data processing was performed using equipment at WAFB, EMSL-LV, and
Northrop Services, Inc., Las Vegas, Nevada (NSI).
2.1 DESIGN AND PLANNING
Planning the study design to satisfy the technical requirements of the
WAFB 1975 project objectives began with identifying both the constituents to
be monitored to characterize dispersion of aircraft emissions and the best
monitoring technology available at that time. Continuous air monitoring
instrument development had progressed to the second-generation status. Data
handling from analog to digital signal processing was well defined. For the
purposes of this study, CO, THC, CIfy, NO, NOX, and nonmethane hydrocarbons
(THC corrected for methane) were selected as the pollutants to be monitored in
order to characterize emissions of both aircraft- and airbase-related
activity.
Given the status of 1975 technology for monitoring CO, NO/NOX, and THC,
it was clear to EMSL-LV that the WAFB project objectives indicated the
following technical requirements:
Assessment of impact would require actual frequency distributions of
emissions from aircraft and indirect sources around WAFB.
Because available dispersion models yield one-hour average
concentrations, the WAFB pollutant measurements would be prepared as
frequency distributions of one-hour averages over a sufficient period
of time to include representative meteorological conditions.
The impact of emissions could be better determined if frequency
distributions observed in areas believed to represent background levels
(i.e., pollutant concentrations relatively unaffected by aircraft
emissions) were compared with frequency distributions in areas known to
be subjected to emissions impact.
-------
LEGtND
or = ACCESS ROADS/
VEHICULAR TRAFFIC
1 A
AIR QUALITY TRAILERS
rjf PERMANENT PROMINENT
BLOGS.
Figure 4. Map of WAFB showing monitoring site locations.
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Although emissions at WAFB were estimated to be higher than those at other
USAF bases and detailed knowledge of WAFB operations was available, the need
for preliminary data was recognized in order to design the air quality
monitoring network and determine the type of meteorological measurements that
would be required.
2.2 SHORT-TERM SPECIAL STUDY
A special study was conducted in an attempt to qualitatively delineate
pollutant transport so that the number and locations of the long-term air
quality monitoring stations could be determined. The study, "Ambient Air
Analysis Survey at Selected Locations," was performed by the USAF, EPA, and
ANL between April 1 and 18, 1975, and included three experiments (the third
experiment was subsequently extended through June 18, 1975): (1) a
grab-sampling effort by ANL at selected locations around the airport; (2) a
single-jet impact study by EPA that included ANL bag sampling; and (3) an
assessment by EPA to determine the adequacy of the Beckman 6800 CO and THC
analyzer. This report covers only those data collected to aid in the design
of the long-term study. (The data are also available in a draft EPA report,
"Air Quality Data Collected by EPA/EMSL-LV at WAFB during the Short-Term April
1975 Airport Study," and portions are discussed in a paper on the overall USAF
study [13]. For further study details, see Appendix B).
A static jet study, using a USAF T-38, was carried out on Saturday, April
5, 1975. This was done to obtain rough estimates of jet plume rise transport
and initial exhaust-plume pollutant dispersion from the jet during engine idle
and power modes of operation. Although estimates for jet plume rise and
vertical and horizontal dispersion parameters are used for air quality
calculations in current airport models, it was believed that these model
parameters could be improved by actual measurement of jet exhaust-plume
dispersion.
A visual concept of the experiment is presented in Figure 5. The sampling
was done from an array of ground stations, established downwind of the T-38,
at which 30-minute integrated bag samples were collected. Data were collected
above ground level (AGL) from two 12.2-m towers and from an EPA H-34
helicopter air monitoring platform. Typical jet emissions during the
experiment were calculated to be approximately 14 grams per second (g/s) CO, 4
g/s THC, and 0.5 g/s NOX. Exhaust temperatures averaged 450°. Although the
average WD during the experiment offset the sampling grid center line by 19°,
the wind varied considerably during each 1/2-hour sampling period, providing
representative pollutant samples. The two 12.2-m towers were located 100 m
downwind, and samples were taken at these towers at elevations of 7.6 m and
12.2 m AGL. The average values for CO and THC (with background subtracted)
are listed in Table 1.
The helicopter data were used to determine the vertical distribution of
NO/NOX, CO, temperature, and scattering coefficient (bscat using a
Meteorology Research Inc. ([MRI] integrating nephelometer). Passes were made
at altitudes between 3.1 m and 42.7 m AGL at downwind distances varying from 0
to 200 m. Jet exhaust plumes were detected at 7 m AGL at 50 m downwind, 20 m
10
-------
o= Sampling locations
= 12 m sampling towers
Figure 5. Sampling grid of single jet study at WAFB.
TABLE 1. AVERAGE CO AND THC CONCENTRATIONS
FOR STATIC JET BAG SAMPLES*
Downwind Distance (m)
Vertical Location
50 100
150
200
Ground (0.9 m)
CO
THC
Tower (7.6 m)
CO
THC
Tower (12.2 m)
CO
THC
17.7
1.05
2.0
1.46
3.9
1.84
3.6
0.00
3.2
0.78
1.0
0.00
* These concentrations are in parts per million (ppm)
and do not include helicopter data.
11
-------
AGL at 100 m downwind, and 21 m AGL at 200 m downwind. (Results from this
test led to an FAA exhaust dispersion experiment at Dulles International
Airport that Recorded air quality data from several 100-foot towers downwind
of taxiing aircraft.) Further detail on the helicopter measurements at WAFB
can be found in Appendix B.
To assess the adequacy of the CO and THC analyzer and to determine the
range of total suspended particulates (TSP), an Airstream trailer equiped with
a Beckman Model 6800 gas chromatograph and a high-volume sampler was set up at
site 1 of the subsequent long-term study (see Figure 4) to monitor ambient air
continuously from April 9 to June 18. The aircraft emissions source area
nearest to site 1 was the queueing area at the southeast end of runways 30C
and 30R, south of the site. The high-volume samples revealed TSP
concentrations ranging from 66 micrograms per cubic meter (wg/m->) to 166
ug/iP, indicating particulate loading in excess of the normal 45 Ug/m^
background concentration measured within a radius of about 25 km from WAFB. A
short-term study was conducted between Aprj.1 9 and 17 to measure THC
concentrations. THC levels increased significantly during the evening of
April 11 and from April 13 through 17. The highest value observed was 9.0 ppm
at 0100, April 16. Throughout the rest of the sampling period, the THC levels
were closer to the expected background level (worldwide background for THC of
1.42 ppm [14]). During this short-term study, there was considerable local
agricultural activity, including chemical spraying, which could explain the
higher levels of THC.
Pollution roses for CO and THC were constructed using April 17 - June 18
data, and the highest third of the concentration values were correlated with
the WD values for each given month. The CO rose for May (Figure 6) represents
all measured concentrations greater than or equal to 0.52 ppm, and it is
representative of the other pollution roses. The highest pollution values
recorded by month for each pollutant, the time each occurred, and the wind
conditions at the time are given in Table 2. The peak concentrations listed
in this table occurred during nighttime and early morning hours when aircraft
activity was minimal and winds were predominantly from the southeast quadrant.
The data in Table 2 suggest that, during nighttime and early morning hours,
off-base sources produce greater concentrations of CO and THC at site 1 than
do airbase flight activities.
The three parts of the preliminary ambient air analysis study provided
pollutant concentration and distribution data and plume transport data for use
in assessing the number and location of stations that would be needed to
answer the technical requirements of the WAFB study. The preliminary study
established a qualitative definition of dispersion and suggested plausible
locations for monitoring sites for the year-long study.
The scope of this task to determine the location of sites included the
need to monitor ground-level emissions from aircraft, and it was realized that
plume rise may prevent measurement in the vicinity of emissions. Thus,
consideration was given to transport and maximum downwind trajectories so that
site locations would be far enough away from sources to allow emissions to
disperse to the ground.
12
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$3°* 3*0* 350'
10* 2O* JO*
40*
310*
300°
50*
SO*
TO*
230*/
I2O*
130°
ISO' ISO*
MO*
Figure 6. WAFB transmitter (site 1) CO pollution rose, May 1975
(concentrations greater than 0.52 ppm).
Local meteorology records were used to assess WD and its influence on
potential (as well as known) source emissions in the WAFB area. Power and
communications requirements, as well as aircraft flight-line safety
constraints, were integrated into the final air monitoring network design.
The locations for the five air quality and meteorology measurement stations
were designated as shown in Figure 4. The criteria used in siting the
stations are summarized in Table 3. Universal transverse mercator (UTM)
coordinates, in kilometers, are included. Sites were selected to continuously
monitor pollutant concentrations within areas of anticipated impact based on
these preliminary data (Appendix B) and logistical considerations of flight
patterns.
13
-------
TABLE 2. SUMMARY OF HIGHEST HOURLY AVERAGES (BY MONTH) FOR
THC, CH4, AND CO DURING 1975 SHORT-TERM
PRELIMINARY STUDY
Month
April
THC
CH4
CO
May
THC
CH4
CO
June
THC
CH4
CO
Highest
Value (ppm)
1.80
1.65
0.8
2.80
2.70
1.02
2.50
2.50
1.30
Day
30
19
19
22
22
10
13
13
17
Time
Hour
0000-0100
0400-0500
2100-2200
2200-2300
2200-2300
0000-0100
2300-2400
2300-2400
2000-2100
Wind
Direction
195°
130°
100°
105°
105°
90°
135°
135°
200°
Speed
4.0
2.5
3.0
2.5
2.5
2.0
4.0
4.0
11.5
2.3 CONTINUOUS MONITORING
Concentration levels measured during the April 1975 experiment indicated
that high instrument sensitivity would be required to detect the lower
concentrations and to monitor both the background levels and any large
excursions of pollutant concentration. Requirements for calibration over this
wide concentration range were also considered important since the assessment
of AQAM accuracy relies in part upon the capability of discriminating between
WAFB emissions that are in excess of background levels. It was confirmed from
the ambient air analysis that CO, CH4, NO, NOX, THC, and meteorological
wind speed (WS) and direction (WD) parameters would be measured continuously
at each station. Light scattering (bscat)> an indirect measurement of
particle mass concentration over a specific size range, would also be measured
at each station. Other considerations in the selection of measurement
instrumentation included the following:
The instrumentation should already have a tested service credibility.
The monitors must operate reliably over a long enough period to provide
data for frequency distributions that are valid over a statistically
acceptable time period.
Calibration and drift from reference "true values" must be acceptable
in order to eliminate excessive calibration adjustment that would
reduce the percentage of recoverable data.
14
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TABLE 3. SITING CRITERIA FOR FIVE AIR MONITORING TRAILERS*
Site No.
> 1 ! 1 ..1
1
2
a.
b.
c.
d.
a.
b.
Location and Siting Rationale
Southeast corner of base; northeast of runways
Continuity with an April 1975 feasibility study
Upwind during early and later morning periods
Power already installed for April 1975 study
Southeast corner of base; immed. northeast of runways
Upwind of T-38 takeoff during morning period (99% of
UTM Coordinates
X Position Y Position
(km) (km)
j_ - -a- -. _ ill - i
440.53 3685.06
all takeoffs and landings at WAFB are southeast to
northwest)
c. Downwind of T-37 and F5 takeoff and taxi route for
all aircraft during afternoon
a. Southeast corner of base; immed. southeast of runways
b. Downwind of T-37 queuing and takeoff during morning
period
c. Downwind of taxi segment for all aircraft during
afternoon
a. Near Building 16
b. Downwind of T-38 apron area during morning period
c. Background to airfield operations during afternoon
period
a. Northwest corner of base; immed. off end of runway
b. Downwind of all airport activities during morning
period
c. Downwind of taxi to shutdown for T-38's and F5's
d. Background location for late afternoon and early evening
440.12
439.29
437.62
3684.60
3684.34
3685.29
* Aircraft in use at WAFB include the T-37 and T-38 trainers and the F5.
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Instrumentation
The following measurement instrumentation was selected:
Gas chromatograph with continuous flame ionization detector for THC,
CH4 and CO in the parts-per-billion (ppb) to ppm concentration
ranges, a wide linear range, and a self-calibration feature
Dual-reaction-chamber chemiluminescent analyzer for NO and NOX in the
ppb concentration range
A nephelometer for light scattering in the visible wavelength (the
measured scattering coefficient is then related to the visible range in
the atmosphere.)
WS and WD propeller vane sensors located approximately 8 m AGL.
Detailed instrument specifications are given in Appendix C.
Monitoring Stations
The five monitoring stations were trailer enclosures (2.5 m wide, 4.3 m
long, 3.1 m high) containing air monitoring and meteorological instrumentation
together with a remote data acquisition system. The five trailer data systems
were connected to the central facility (located in Building 16) through
dedicated telephone lines; separate lines provided voice communications
between trailers and Building 16. Each monitoring station shelter was a
Westinghouse Air Quality Mobile Enclosure housing the monitoring
instrumentation (Figure 7). A heat/cool air conditioner was used to maintain
a relatively constant trailer temperature.
The air sampling manifold for a monitoring station (Figure 8) included a
glass ballast chamber upstream from the CO-Clty-THC analyzer to provide a
sample air residence time (ratio of volume to flow rate) of at least twice the
data system interrogation rate (each minute of the hour). This chamber was
procured and installed by the contractor after station interrogation rates had
been determined in May 1976. The chamber allowed the averaging of transient
high concentrations of CO, Ctfy and THC that would otherwise pass unobserved
and accommodated the 5-minute sampling and analysis cycle of this analyzer. A
separate 5-centimeter (cm) diameter inlet line, free of any angles, was made
for sampling with the integrating nephelometer so as not to stratify the
particulate sample prior to entry into the nephelometer.
Data Collection
The stations of the monitoring network were linked to a central data
acquisition unit in Building 16. Each monitoring station was interrogated
each minute of every hour. Stations 1 through 5 were polled each time in the
same order* As the station was polled, the remote data system in each trailer
scanned the voltage output of all air quality and meteorological sensors.
Voltage from each station was then recorded on magnetic tape at the central
data acquisition area. Time, trailer number, and operational status coding
16
-------
NO, NOX
MONITOR LABS
MODEL 8440
ESTERLINE ANGUS
MODEL LI 1-028
LAB RECORDER
{CALIBRATION, ETC.)
THC.Cfy.CO
BECKMAN
MODEL 6800
PARTICULATES
MR I INTEGRATION
NEPHELOMETER
DATA COLLECTION
MONITOR LABS
MODEL 9400
WIND SPEED/DIRECTION
R.M. YOUNG
MODEL 35003
PROPELLER VANE
CENTRAL DATA COLLECTION
(mag. tape)
Figure 7. Block diagram of trailer instrumentation.
SWEEP ELBOW
AIR SAMPLING CONE WITH FUNNEL
ROOFATTACHMENT
AIR SAMPLING MANIFOLD
t
25mm BUSHING
MIXING CHAMBER
FOR
BECKMAN 6800
BLOWER MOUNT
BLOWER
-EXIT
Figure 8. Air quality intake system.
17
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for instruments and each data channel were logged for each air quality or
meteorological parameter. The instrument basic to the central data
acquisition unit was the Monitor Labs (ML) Model 9400. It digitized the
analog output from the air monitoring instruments and transmitted the
information to the central data system upon request (Figure 9). The system
was equipped with 10 data switches that were used to transmit instrument
status data according to thumbwheel codes at each station. Additional data
acquisition system specifications are given in Apendix C.
MONITOR LAB
9400
REMOTE
TELEPHONE
I NTERFACE
MONITOR LAB
9400
REMOTE
MONITOR LAB
9400
REMOTE
TELEPHONE
I NTERFACE
TELEPHONE
INTERFACE
COMMERCIAL TELEPHONE LINE
(PLAYBACK)
HEWLETT-BXCKARD
9830 A
CALCULATOR
c
MAG
TAPE
MAG
TAPE
(EDITING)
LINE
PRINTER
MONITOR LAB
9400
REMOTE
MONITOR LAB
9400
CENTRAL
C
MAG
TAPE
(MAINLINE RECORDING)
Figure 9. Data collection system.
2.4 ADDITIONAL METEOROLOGICAL INSTRUMENTATION
Additional meteorological instrumentation was used throughout the
monitoring period. These included a pyranometer that collected data for most
of the monitoring period at site 4, orthogonal wind sensors and temperature
instrumentation installed in April 1977, an acoustic sounder operated
continuously near Building 16 from June 1976 through June 1977, and boundary
layer profile sensors. The sensors were used to provide further resolution of
winds and temperatures in the vertical when compared to results from the
acoustic sounder.
18
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An Aerovironment Model 300 monostatic acoustic sounder was used to provide
information from the interaction of acoustic waves with the atmosphere. These
data indicated the various depths of the mixing layer and the time of
inversion breakup (at the top of the mixing depth). They also provided
information on the vertical mixing properties of the atmosphere and (as input
for model calculations) insight into atmospheric stability. The control and
recorder unit was located in Building 16, and the dish-shaped transmit/receive
antenna was installed inside a trailer-mounted Model 301 acoustic enclosure
(2.4 m high, pentagonal in shape) about 17 m west of Building 16. The
recorder-acquired data and daily chart removal were timed to coincide with the
magnetic tape changes or the calibration of monitoring stations.
A "u,v,w" propeller anemometer made by R. M. Young was installed at the
top of the WAFB "boom" bucket tower (30 m high). An Environmental Systems
Corporation delta temperature system, Model PTS-80A, was also installed. Data
from these instruments are available from April 1977 through June 1977. These
micrometeorological data were requested by ANL to provide them the opportunity
to calculate stability parameters at WAFB in the event that data comparison
showed model revision was necessary. Estimates of emission dispersion of
parameters can be improved in the modeling phases of the study through the use
of actual data characteristic of the atmospheric potential to disperse
emissions.
Measurements with these meteorology instruments included one-minute
orthogonal wind components (u,v,w) in the x,y and z directions and temperature
and temperature difference over a 30 m vertical height.
2.5 MONITORING OPERATIONS
Monitoring operations and the quality control to maintain operations
within acceptable limits were specified and monitored by EMSL-LV. Certain
meteorological instrumentation was added to the study in June 1976, as
described in subsection 2.4. A summary of all the instrumentation,
calibration requirements, and the period of monitoring is shown in Table 4.
The monitoring trailers (stations) were constructed at WAFB with
Government-furnished equipment under EPA contract and technical direction.
The trailer system tabulation, installation, and integration to the data
system were also done under EPA contract. The stations were operated by USAF
technicians from the 6th Mobile Weather Squadron and by EPA contract personnel
resident at WAFB.
Fabrication and assembly of the monitoring trailers took place at Building
16 at WAFB, located near site 4. When power became available in March 1976,
the trailers were moved to their site locations and stabilized on jacks, and
the air sampling manifolds were assembled. Overall system checkout and
periodic maintenance and calibration activities began in May 1976, and data
acquisition began in June 1976.
19
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TABLE 4. INSTRUMENTATION SUMMARY
Parameters
Measured
NO/NOX
CO
Instrumentation
Monitor Labs 8440 (dual-chamber
chemilumine scent)
Beckman 6800 (gas chromatograph
with flame ionization
Calibration
Requirement
NO gas cylinder with 50 to
100 pm and dilution to
0.4 ppm
AADCo pure air generator
Low concentration cylinders
0.1-0.5 ppm
Gas cylinder with span concen-
trations from 3 to 5 ppm
Period
Covered
1 June 1976 -
30 June 1977
1 June 1976 -
30 June 1977
THC, CH4
detector)
Beckman 6800 (gas chromatograph
with flame ionization)
Light scattering MRI model 1550B nephelometer
R. M. Young propeller vane
Aerovironment Model 300
acoustic sounder
R. M. Young Gill propeller
vane
WS/WD
Mixing depth
U,V,W (orthog-
onal winds,
30 m AGL)
Solar insolation Pyranometer
Gas cylinder with span concen-
trations from 3 to 5 ppm
Freon 12 cylinder and pure air
from internal source
Constant speed motor (1800
rpm, theodolite alignment
on north, 13°30'E declination
Independent measurements of
temperature in the vertical
Maintain electronics, constant
speed motor (1800 rpm)
Manufacturer's specification,
EPA #126564
Maintain electronics
AT
E.S.C. Model PTS-80A
Calibrated by manufacturer
1 June 1976 -
30 June 1977
1 June 1976 -
30 June 1977
1 June 1976 -
30 June 1977
1 June 1976 -
30 June 1977
6 April 1977 -
30 June 1977
*15 July 1976 -
25 January 1977
21 January 1977-
30 June 1977
6 April 1977 -
30 June 1977
* Two sensors were used. Monitoring eriods were overlaped to check reproducibility.
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Building 16 served as the onsite study headquarters where operations of
the air quality monitoring network, data acquisition, preliminary data
processing, and .related special studies were coordinated. Laboratory
operations, maintenance, administration, supply, and receipt of daily weather
reports were also performed in this facility. Weather observations, essential
to the AQAM model, were provided by: 1) USAF personnel using Federal
Meteorological Form 1-10 (WABAN Form 10), "Surface Weather Observations"; 2)
acoustic sounder codes; and 3) the WAFB weather station, which assembled data
on a tape for the entire monitoring period.
Systems Performance
Before the beginning of the study, EMSL-LV specified the data record
format to appear on the digital magnetic tape recorder and line printer-
Also, digitized analog signals from the station instrumentation were
demonstrated to be compatible with the digital data system of the ML 9400
central data acquisition unit. Systems performance was considered acceptable
when:
The analog signal inputs from air quality instruments and data switch
(thumbwheel) information at each of the five monitoring stations was
consistently interrogated by the central data system and reproduced on
the mainframe digital-magnetic tape line printer.
The central station could consistently poll or interrogate each
monitoring station in succession.
The digital characters on the line printer were the same as those
transmitted from each data system, and nonvalid or misplaced characters
did not appear in the recorded format.
The performance goal for WAFB air quality measurement was 80 percent
recoverable data at the line printer.
The WAFB field operations were monitored by EPA during the two months
prior to June 1976 to demonstrate that the five mobile stations and the
central data acquisition system conformed to the original EPA plan. This
inspection consisted of two parts:
1. Reviewing all trailers and central data acquisition equipment to
ensure proper procedures for:
Stabilization of trailers
Physical mounting of instruments and auxiliary equipment
Electronic and electrical connections
Installation of ambient air sampling manifold
Safety practices and procedures
21
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2. Demonstrating valid operation for the Beckman Model 6800 gas
chromatograph, ML NO/NOX analyzer, MRI nephelometer, Gill propeller
and ML data system through:
vane,
Calibration
Operation in the continuous mode for ambient air sampling
Accurate transmission of data from the data acquisition system as
voltage printouts for air quality sensor responses to the central
data ML 9400 magnetic tape.
The WS and WD instruments were aligned by Air Force (AF) personnel using a
constant-velocity calibrator and theodolite. The AF took one tape of air
sensor data for overall system evaluation and approved the EPA operating
plans.
The station instrumentation was also evaluated in relation to previously
established performance specifications for air quality parameters. These
specifications included span and zero drift, range, and response or rise time
(Table 5). Instrument manufacturers' performance specifications for the
analyzers used at WAFB are given in Appendix C, and detailed calibration
procedures are described in Apendix D. In the absence of any previous
site-specific air quality measurements, it was anticipated that the analyzers
selected would be adequate in the concentration ranges of interest.
TABLE 5. PERFORMANCE SPECIFICATIONS
CO THC and CH. NO and NO
4 x
3scat
WS and WD
Range
0-10 ppm 0-10 ppm 0-.5 ppm 0. l-lOxlO'V"1
Zero drift + 5%/day + 5%/day + 5%/day
Span drift + 5%/day + 5%/day + 5%/day
Precision +5% +5% +5%
3%
4%
0-22 m/s
0-352°
+ 5%
Operations Procedures
The monitoring network at WAFB was subjected to a daily routine of
maintenance and inspection. The operations procedures used to maintain the
monitoring network are summarized in Table 6. The station inspection forms
(Appendix E) were reviewed to identify out-of-tolerance conditions. Systems
malfunction usually involved operator error with the data coding switches
(thumbwheels) used in making the daily zero and span checks (see Appendix F).
22
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TABLE 6. OPERATION AND CALIBRATION SCHEDULE FOR MONITORING NETWORK
Procedure
Schedule
Function
Trailer insection
Zero and span check
(unadjusted)
Calibration adjustments
Maintenance
Factory service
Daily
Daily
Preventive maintenance to meet
performance specifications
Monitor instrument status,
trend, and drift; develop the
calibration array to correct
data
One time per Reference to secondary standards
week, not to to calibrate data
exceed 10 days
As required
As required
Maintain operational status of
sensors
Procurement and maintenance of
manufacturers' specifications
2.6 QUALITY CONTROL
Quality control procedures at WAFB, in effect by June 19, 1976, consisted
of detailed instruction (including calibration procedures) given to the USAF
technicians and contractor personnel, the maintenance of standard reference
gases, and recordkeeping for control charts. These procedures were
implemented through daily inspection of the trailers and associated
instrumentation; zero and span control checks, including a written record of
unadjusted calibration values; and calibration corrections and adjustments.
Station Inspection
Air quality analyzers and meteorological instrumentation were operated 24
hours per day, 7 days per week, for the 13-month study. Monitoring stations
were inspected each morning by the USAF technicians, using the Trailer
Inspection Checklist (Appendix E). Experience showed that this was an
appropriate schedule to maintain the operation of the network. Visual checks
for physical damage to the station sensors and intake manifold, as well as
status of station supplies (e.gi} drierite, water levels, and strip-chart
paper), were a part of this routine. Discrepancies were noted by the USAF
personnel and brought to the attention of the resident contractor field
engineer for corrective action. After the daily station inspection, a
calibration term was dispatched to the monitoring site that had been selected
for calibration. The daily inspection provided input for decisions made by
23
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this team concerning changes in calibration (e.g., for a malfunctioning
instrument).
Zero and Span Checks
The air monitoring instruments were checked daily to evaluate zero and
span drift. During the zero and span checks, no attenuator adjustments were
made on the instruments. The data were recorded on calibration check sheets,
and the recorded data were tagged with a thumbwheel code in the data system so
that the values could be retrieved during conversion of output voltages to
pollutant concentration units (engineering units). These check values were
used in the data processing operation for correcting data for zero and span
fluctuations. The values were also used to construct control charts, which
were analyzed to evaluate instrument performance on a continuing basis. The
WS and WD instruments were not checked as frequently because of their
reliability and simplicity.
Typically, one station was checked at a time. The order was altered from
day to day so that a station was not checked at the same time on successive
days. This helped to avoid systematic bias that could cause error in the
collection of calibration check data. The procedures for this operation
included a check of thumbwheel settings, wind azimuth, ML 8440 NO/NOX
analyzer, MRI nephelometer, and Beckman 6800 gas chromatograph. The
step-by-step sequence is shown in Appendix E. USAF and contractor personnel
recorded all the data from the calibration sheet onto permanent logbooks that
remained at the stations. The positions of all the data switches on the
calibration check sheet were also recorded for use in data processing.
Station Calibration
Once a day at the beginning of the study (and less frequently thereafter),
the air monitoring instruments in each of the five stations were checked by
USAF technicians, and adjustments were made to the zero and span calibration
values. Initially, this calibration required up to 15 hours per day. Later,
the frequency of adjusted calibration was specified for each air quality
monitor, to occur at intervals of no less than 10 days, unless repair was
called for (which would also require recalibration).
Daily site calibration was based on the following criteria:
Instrument performance was indicated by the previous day's zero and
span checks, as well as the results of the morning trailer inspection.
Assuming no specific problems, trailer selection for calibration was
made so that trailers were not calibrated on the same day of each week.
Scheduling was arranged to ensure that a trailer went no longer than 10
days without calibration (see Table 6).
A wheeled cart containing the dilution calibration system was used to deliver
calibration atmospheres at different concentrations for the NO/NOX analyzer
at each station. A mobile van was used to transport the Bendix Model 8851X
24
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Dynamic Calibration System (BDCS), the AADCo zero air generator, Model 737,
calibration gas cylinders (NO/NOX), and compressors with silencer housing
from site to site (Figure 10).
Calibration Gases
Air monitoring calibration gases, used in the production of test
atmospheres for calibration activity, were obtained from certified vendors.
Upon receipt of the gases, the vendor analysis was verified by cross-
comparison to local gas standards, and the gases were subsequently
cross-compared and analyzed at regular intervals to check for changes in
concentration. The list of calibration gases, their use at each location, and
dates of use are given in Apendix G.
In practice, the calibrations of the instruments were performed
simultaneously and not as discrete steps. After the calibrations were
completed, the instruments were allowed to stabilize. During this time the
calibration values were recorded in logbooks provided for each instrument.
The calibration sheets were maintained as a permanent record and were used to
construct control chart graphs of instrument performance.
MONITOR LAB 8440
(manual)
(NO/NOX)
CALIBRATION GAS
quick disconnect
-H
AADCO
MODEL 737
ZERO AIR
BENDIX
MODEL 885IX
DCS
AIR
COMPRESSOR
BECKMAN 6800
(automatic)
HYDROGEN
GENERATOR
ZERO AIR
GENERATOR
BECKMAN 6800
MONITOR LAB
8440
(CO/CH4)
CALIBRATION GAS
Figure 10. Calibration system for air quality trailers,
25
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SECTION 3
DATA PROCESSING
Data processing activities for the WAFB project consisted of the
following:
Handling one-minute data tapes acquired from the air monitoring network
(see Section 2) and verifying the contents of these tapes (Tape I)
Calibrating the one-minute voltage tapes and converting the voltages to
engineering units (Tape II)
Averaging the one-minute data to produce hourly averages and
calculating the root mean square average, the standard deviation, and
the maximum and minimum for each hour (Tape III)
Coding WABAN meteorological data onto computer forms and tape
cartridges and merging this data into a data file of consistent format
for each month that air quality data were collected (Meteorology Tape)
Presenting data in the form of tabular listings of hourly data,
frequencies, and cumulative frequencies of NO, CO, NMHC and
nephelometer; cumulative frequency distribution plots of these four
parameters; time plots of the hourly averages; time plots of minute
values for four Julian days; and microfiche of the tabular listings
Compressing 395 Level II tapes onto 20-reel set for future analyses
Digital voltage data from each of the five monitoring stations were
recorded at one-minute intervals on magnetic tape in the central data
acquisition facility (Building 16) at WAFB. Procedures were developed to
convert the one-minute air quality data to hourly averages. The
hourly-averaged data are presented in tabular summaries and monthly lots of
concentration versus time. Data included the continuous air quality and
meteorology data taken from the air monitoring network over a 13-month period.
Processing required several levels of interactive editing with the use of
control charts of zero, span, and calibration information to support data
correction and adjustment. Checks for internal consistency were uniformly
applied during data processing, and transmittal errors and rejected data have
been identified in Appendix I.
Meteorology data collected as hourly observations on WABAN forms were
coded by the USAF and provided on one magnetic tape. This tape also included
the mixing-depth information from the acoustic sounder. Additional
meteorology data collected at monitoring station 4 from April to June 1977 are
26
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available on the one-minute magnetic tapes collected in the central data
acquisition facility.
Data were accepted or rejected through editing, verification, and
screening based on a predetermined set of criteria. The goal in processing
was to assure that corrections were made for causes documented in operations
logbooks for each monitoring station of the network.
The WAFB data were referenced to calibration standards at intervals as
shown in Appendix G. Data from each monitoring station were referenced to
transfer standards and also to primary standards to establish traceability to
known concentrations as provided through the vendor. Uncertainty of
calibration traceability was accomplished through vendor analysis and
in-laboratory evaluation.
Prior to data processing, some data were examined to determine if they
were representative and reasonable. Limits of acceptable analyzer values for
a one-minute value (x) of each air quality parameter were specified as follows
with regard to measurement concentration ranges encountered, instrument
manufacturers' specifications, and measurement experience at WAFB prior to
June 1976 (see the minute-to-hourly-average data reduction program in
Appendix I):
NO: -0.05 < x ^ 0.49 (ppm)
NOX: -0.05 < x ^ 0.49 (ppm)
CH4: 1.3 < x <£ 7.9 (ppm)
THC: 1.3 ^ x ^ 7.9 (ppm)
CO: 0.0 < x <: 7.9 (ppm)
NEPH: 0.0 < bscat | 9.9 (lO'V"1)
3.1 AIR QUALITY DATA
The air quality data base from the fixed monitoring sites, recorded in
one-minute intervals, included data for CO, Clfy, THC, NO, NOX, bscat, WS
and WD. NMHC data were obtained by subtracting City concentrations from THC
concentrations (measured as CH4), after the CH4 and THC one-minute data
had been converted to hourly averages.
The sequence of the data processing included the production of a series of
four magnetic tapes, each a result of successive editing. Detailed procedures
used for the production of these tapes are given in Appendix I. The four tape
series included:
Tape I Series - 395 seven-track tapes containing the raw one-minute air
quality and meteorological data voltages acquired by the monitoring
network stations as they were polled by the ML data acquisition system.
27
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They are unedited and uncorrected and so include the effects of
instrument calibration adjustments and instrument malfunctions. They
also include data for periods of time when related special studies were
being conducted during which the percentage of recoverable data was
reduced. Voltage values for u,v,w and AT data are included in the
record of monitoring station 4 for the three-month period from April
through June 1977.
Tape II Series - 395 tapes containing edited one-minute data as a
result of performing the following processes on the Tape I data:
- Extract calibration information.
- Apply calibration and zero-drift corrections.
- Convert from voltages to engineering units.
- Remove any data known to be invalid as the result of instrument or
operator error (as noted in station logbooks).
Tape III Series - 13 tapes containing hourly averages and statistics
computed from the one-minute data on the Tape II series. Each Tape III
contains hourly averages for a complete calendar month.
Meteorology Tape - One tape containing meteorology information
transcribed from WABAN reporting forms summarizing weather observations
at WAFB. Acoustic sounder u,v,w and AT data are appended to the WABAN
information.
3.2 METEOROLOGY DATA
The meteorology data for WAFB were obtained from hourly WABAN observations
coded by the USAF and produced separately from the air quality data record and
from coding sheets listing acoustic sounder mixing depth. The meteorology
data were then transferred to nine-track magnetic tape. The process for
producing this tape is shown schematically in Figure 11. The tape format and
character locations are shown in Appendix I. Meteorology data in the air
quality data base were processed to become a part of the AQAM model input.
The acoustic sounder data were recorded on conducting chart paper, and
daily chart removal was timed to coincide with the daily change of magnetic
data tape (at 1,100 hours) from the air monitoring stations. This procedure
facilitated the comparison of acoustic sounder and magnetic tape data and kept
the acoustic sounder chart to a workable length for coding. Upon removal,
each chart was trimmed to a uniform size and coated with a clear plastic spray
to prevent smudging. Since the chart speed was not always uniform, the start
and stop times and dates were written on each chart so that one-hour time
marks could be located accurately. The time marks were drawn in for every
hour on the half hour so that the average hourly acoustic sounding returns
could be determined on the hour. The original records for the 13-month
sampling period are maintained in Las Vegas.
The procedure for coding and placing the acoustic sounder data on the
Meteorology Tape is presented in Appendix J. It allows the data user to sort
28
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MAGNETIC
TAPE CARTRIDGE
WAFB
9-TRACK
FORMATED
MAG
TAPE
Figure 11. Base meteorology data processing steps.
the WAFB data according to various atmospheric conditions. Mixing depth is
critically important to model calculations. The classification codes can be
made specific to any study and locale. The six-digit code for each averaged
hour indicates the phenomena observed for example radiation inversion,
drainage winds, layered returns, lifting inversion base, subsidence inversion,
frontal inversion, or normal daytime return. In addition, the heights of the
various phenomena are listed.
The one-minute wind data from Tape I series (which were edited as a part
of the Tape II process) were used to calculate one-hour wind averages for
one-month increments (Tape III series). Final editing on the Control Data
Corporation (CDC) 6400 Computer resulted in site-specific WD and WS for each
of the stations for the entire monitoring period. Representative plots
(Figures H-l to H-91, Appendix H) show daily and monthly horizontal wind
patterns. WS and WD studies with the Gill propeller vane sensors are
discussed further in Appendix B, Related Special Studies.
29
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3.3 DATA SUMMARIES
A complete 13 months of data from each monitoring station were tabulated
in hour averages on the CDC 6400 and are archived at Tyndall AFB, ANL and
EMSL-LV. Bound copies of these summaries will be maintained at Las Vegas
until interpretation by the USAF and ANL is complete, at which time archival
will be through microfiche only. The hourly-averaged concentrations for each
air quality parameter are columned together with the daily average and the
maximum for each 24-hour period. Irrecoverable data resulting from those
periods when instruments were being calibrated, were inoperative, or were out
of control because of operator error, as well as nonvalid data, are designated
by 9's in the tabular summaries. The trailer data (generated in the following
order: NO, NOX, CH4, THC, CO, NMHC, NEPH, WD, WS) consist of a total of
520 computer printout sheets.
The hourly averages for each of the air quality parameters were plotted
for each month. These plots (Figures H-l to H-91, Appendix H) show the hourly
averages of each pollutant as well as daily and monthly horizontal wind
patterns, for all trailer sites of the monitoring network on one page per
month. They illustrate station-to-station variation of pollutant
concentration and provide the user with the opportunity to select a time, a
pollutant, or a section of particular interest for more detailed understanding
and analysis.
The time series plots present one-minute data over a 24-hour period, and
they allow the user to pinpoint the absence of, or effects from, aircraft
emissions. Daily plots from September 28, 1976, December 29, 1976, January
27, 1977, and May 11, 1977, of the monitoring period are presented in
Appendix H, Figures H-92 to H-134. These plots demonstrate excursions of
pollution concentrations typical of the WAFB environment.
The locations of all data (tapes and tabulated data) are summarized below:
Magnetic Tapes I (raw one-minute data) and II (edited one-minute data)
are located at EMSL-LV.
Tape III series (the corrected hourly averages for air pollutant, WS
and WD data) are located at EMSL-LV and are also in the possession of
ANL in Chicago, Illinois.
Tabular summaries, cumulative frequencies, and graphics are located at
Air Force Engineering and Services Center/RDVA, EMSL-LV and at the
Tyndall AFB, Florida.
30
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SECTION 4
DATA ANALYSIS AND EVALUATION
This section presents an analysis and evaluation of data obtained from
continuous air monitoring at WAFB during the period June 1976 through July
1977. The purpose of this evaluation is to summarize data and assign
appropriate limits for measurement accuracy (relative to average annual
conditions). This summary will provide insight to the USAF contractor
(Argonne National Laboratories) for use in performing the AQAM accuracy
definition analysis.
To provide assurance of data validity, data were analyzed to determine
confidence limits imposed by measurement precision. This was accomplished by
reviewing calibration and calibration check data. Evaluation of the data base
began by comparing the amount of air quality and meteorological data collected
to that which would be sufficient to conclude that sampling had occurred
during all representative meteorological conditions. Additional data analyses
were performed to relate measured values to existing ambient air quality
standards.
Estimates of measurement recision at -WAFB in terms of pooled precision and
calibration bias have been developed through reference to secondary standards
for which statements of uncertainty have been provided by the vendors of
calibration gases. Cumulative frequency distributions are presented in
Appendix K to indicate the ranges of the data at each monitoring location and
provide a graphical means for comparing relative measurement error between
stations.
4.1 DATA RECOVERY
The percent-recovered data (shown in Table 7) account for 71 percent of
the total time (pooled average) in the 13-month monitoring period. Tabular
summaries of hourly averages for each air quality parameter (discussed in
Section 3 and given in Appendix H) were produced from valid data tests that
reduced the one-minute data recovery by about 10 percent. These data were
discarded for the following reasons:
They were out-of-tolerance, being outside the minium and maximum
concentration range for the instrument sensor.
They had errors resulting from systematic variations discovered in
interactive editing (verified with operator and instrument logs).
31
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TABLE 7. PERCENT DATA RECOVERY FOR FIVE MONITORING STATIONS OF WAFB STUDY
to
June 1976
July 1976
August 1976
September 1976
October 1976
November 1976
December 1976
January 1977
February 1977
March 1977
April 1977
May 1977
June 1977
Total Average
(NO)
NITRIC
OXIDE
90.0
89.9
86.0
59.1
84.7
' 76.2
69.4
56.2
52.2
45.7
87.9
72.7
69.3
72.3
(NO )
OXIDfiS OF
NITROGEN
89.9
89.9
86.9
59.5
88.4
81.2
69.4
52.7
52.2
45.3
87.9
73.7
69.6
72.8
(CH4)
METHANE
74.1
71.4
74.6
70.3
79.6
68.0
71.4
61.1
50.1
44.5
86.4
72.2
69.5
68.7
(THC)
TOTAL
HYDROCARBONS
58.9
70.6
75.1
70.5
79.0
72.9
73.5
59.8
51.0
45.4
86.5
72.5
70.3
68.2
(CO)
CARBON
MONOXIDE
74.5
74.5
79.7
70.7
79.8
70.5
68.2
62.1
51.1
45.6
86.6
72.2
70.3
69.7
(NMHC)
TOTAL
HYDROCARBONS
-METHANE-
54.9
69.2
71.3
69.8
78.3
£8.0
71.4
58.8
50.0
44.0
86.2
72.2
69.5
66.4
(VMWD)
VECTOR MEAN
WIND DIRECTION
91.5
93.1
78.1
74.6
92.7
70.2
69.8
51.1
52.3
48.0
87.0
74.5
71.0
73.4
(VMWS)
VECTOR MEAN
WIND SPEED
91.5
93.1
78.2
74.6
92.7
70.2
69.8
51.1
52.3
48.0
87.0
74.5
71.0
73.4
-------
Tabular summaries were examined to find out which monitoring stations were
responsible for low recovery of data. This was done to confirm that data had
been discarded for a reasonable cause. For example, station 1 of the
monitoring network had a remote data system failure in May 1977 that was not
repaired for the remaining period of monitoring. The highest data recovery
took place in April 1977, and the station 1 data system failure reduced the
percent recovery for the remaining months of the monitoring period.
Records for station 2 confirmed a problem in THC measurement for June
1976. Even though City and CO data were recovered at a level of 75 percent,
THC and NMHC (THC minus CH4) were less than 60 percent recovered. Logbook
entries and troubleshooting notes confirmed that this instrument had valve and
chromatographic column failures in this month. Wind sensor failure occurred
at station 2 in January 1977, as supported by the station logbook entries.
Station 3 data recovery was greater than 70 percent throughout the
monitoring period. Station 4 experienced about 70 percent downtime in
February from data system failure. After the initial problems with the
hydrocarbon monitor in station 5, data recovery was considered average (about
70 percent), with the exception of the January through March 1977 central data
acquisition problem that affected all stations.
An analysis to show percent valid data capture on one-minute series tapes
was not performed. However, one-minute data that did not meet one-hour
average data processing requirements can be recovered from archived data
(Appendix I). Monitoring operations and quality control procedures accounted
for approxiately 16 percent interruption of one-minute data recording from the
monitoring network.
Prior to monitoring, the time estimated for operational quality control
and downtime for preventive maintenance was 8 percent. Capture of one-minute
data at the line printer would have been about 92 percent if unscheduled
maintenance, operator error, and data system failure had not occurred.
Unscheduled maintenance for power, air-conditioning, and data system failure
caused additional portions of the network to be inoperative an additional 8
percent of the time. Overall downtime was sampled from station logs for
stations 2 and 3 and is shown in Table 8 to provide an example of system
downtime during the monitoring period.
TABLE 8. SYSTEMS DOWNTIME AT STATIONS 2 AND 3
Operation Percent Inoperable
Preventive maintenance 4
(unadjusted checks)
Calibration (adjusted) 3
Power failure 3
Air-conditioning 4
Data system failure 1
33
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The frequency of maintenance and repair was not fully anticipated, and
replacement analyzers were necessary to avoid excessive downtime. High-
maintenance problems are listed below in descending order of importance:
Continued repair of NO/NOX sensors, with high downtime for 03
generators
Hydrogen generator failure for CO, CH4 and THC analyzers
Power outages
Air-conditioning failure, causing air quality instrument drift
4.2 WIND SPEED AND DIRECTION INSTRUMENT PERFORMANCE
The Gill propeller vane instruments used to collect the WD and WS data are
highly reliable with a projected useful life of 2 to 4 years for WS and 3 to 5
years for WD under conditions of normal operation. Directional alignment at
each monitoring station was established with a theodolite and checked twice
with a sight compass, once during and once near the end of the monitoring
period.
The wind azimuth range used was 0° to 352°, giving optimum linearity over
the active range of the wind-direction scale. Zero and span instrument checks
were done, although WD was not checked routinely. Estimates of the standard
deviation of the wind direction instrument are one percent of the voltage
output signal for azimuth during the monitoring period. Sight compass checks
of sensor alignment indicated a repeatability of +3° azimuth. WS was
calibrated when instruments were replaced or repaired because of malfunction.
These calibrations were performed with the USAF synchronous calibrator, and
measurement uncertainty in WS is estimated at +5 percent.
Table 8 shows that an average of 73'percent of the wind data were
recovered for the monitoring period. Low January, February, and March
recovery resulted from failure of the central data acquisition system.
Recovery after April was affected by failure of the remote data system at
station 1.
To compare the trailer WS and WD sensor output with that from the WAFB
anemometer (as recorded on WABAN coding sheets), data from October 1, 1976,
were examined. Since the station readings were instantaneous values recorded
once per minute and the WABAN values were one-minute readings recorded hourly,
correlations cannot be made by simply comparing the two measurements. As a
result, readings from station 2 (in the proximity of the base anemometer) were
averaged for 5 minutes before and 5 minutes after each reported time of WABAN
measurement. These averages were then compared to the WABAN values for 23
hours on October 1. Graphs were constructed to display the results.
For WD data, the changes recorded at station 2 matched those of the base
anemometer in terms of shift in direction (clockwise or counterclockwise),
with a positive bias for the trailer values. The average station 2 value was
34
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approximately 11 percent greater than the WABAN average for 23 hours (152° vs.
138°). As expected, there was consistent agreement for changes in WS although
no high or low bias was observed in terms of wind speed magnitude. The
average WS at station 2 was approximately 11 percent higher than the WABAN
average for the same 23-hour period.
4.3 PERFORMANCE OF CONTINUOUS AIR QUALITY ANALYZERS
Analyzer Performance Characteristics
The principles of measurement utilized at WAFB are discussed in detail in
Appendix C of this report. Further discussion is warranted regarding actual
measurement precision and accuracy, particularly for the Beckman 6800
analyzer, which uses flame ionization detection to measure both total hydro-
carbons and carbon monoxide as methane. The original monitoring objective for
WAFB, established for modeling purposes, required the collection of useful
ambient data over the full range of concentrations identified during the
preliminary study performed by the EPA in 1975. This monitoring objective
required the measurement of CO air quality levels below the minimum detectable
limit of the EPA reference or equivalent method for CO, the nondispersive
infrared principle.
Since jet and vehicular emissions at Williams AFB were to be monitored in
terms of CO, NOX, and hydrocarbons corrected for methane, the selection of
measurement method was important. The gas chromatographic separation of CO,
CH4, and higher hydrocarbons (with subsequent analysis as methane) has
advantages over other sampling and analytical procedures for these species.
Hydrocarbons corrected for methane (reported as NMHC) are important in
relation to oxidant formation although no NMHC standard is rigorously applied.
A three-hour average (from 6 a.m. to 9 a.m.) of 240 ppb is a recommended
guideline with respect to NMHC as precursors for photochemical oxidants.
Ambient atmospheres in the Western United States have annual mean CO
concentrations of 200 ppb or less in nonurban areas, and concentrations as low
as 50 ppb have been recorded in background areas [15]. The recognized
procedure, which is sensitive at these concentrations, is to convert the CO to
methane ad measure CO as methane with a flame ionization detector* Analyzer
calibration requires sophisticated equipment and techniques. This procedure
is incorporated in the EPA reference method for measuring NMHC as hydrocarbons
corrected for methane.
However, unacceptable measurement discrepancies between various instrument
configurations and different operators have been reported for this method of
measurement. Variation between flame ionization detection hydrocarbon
analyzers (when used to measure ethane, ethylene, and acetylene) have been
observed to be substantial. The standard deviation for these variations in
hourly-averaged NMHC data ranged from 217 to 454 ppb [16]. Therefore, to
obtain useful data, additional quality control procedures were implemented for
the gas chromatographs used at WAFB. In contrast to normal procedure where
calibration is performed weekly, daily zero and span checks were made to
control chromatographic separation efficiency and other routine operating
35
-------
factors. This method, while still the most accurate for measuring CO
according to EPA audit performance tests [17], has poor precision for NMHC.
However, in the concentration range of interest at WAFB, there was no other
method suitable for use in monitoring previously observed levels for
hydrocarbons or CO.
Measurement uncertainty (in terms of precision) for the CO and hydrocarbon
analyzer used at WAFB is less than that published in other reports. Daily
calibration checks were responsible for the relatively good precision.
Additional technical data were collected in the laboratory using the analyzer
from station 1 at WAFB to develop repeatability precision at concentrations
comparable to those encountered during monitoring. These data indicate that
analyzer performance for the Beckman 6800 will exceed published limits when
the instrument is operated under controlled conditions similar to those
imposed at WAFB.
Operation of the station 1 Las Vegas analyzer in the laboratory was
identical to that at WAFB. Test atmospheres of Clfy were introduced at
levels of 3.0, 1.5, 1.0 and 0.0 ppm. Standard deviations of calibration were
determined to be 0.014, 0.006, 0.003 and 0.001 ppm, respectively, over a
four-day period. Repeatability precision (average) at the 95 percent
confidence level for THC and CIfy response to methane was found to be
0.016 ppm, and precision for hydrocarbons corrected for methane was 0.023 ppm.
CO test atmospheres were introduced to the analyzer at 3.0, 0.2 and 0.0 ppm.
Standard deviations observed were 0.02, 0.01 and 0.006 ppm, respectively, and
average precision for CO was 0.046 ppm. This relatively high precision can be
attributed to the laboratory environment, operator skill, calibration
apparatus, and techniques used. Based on the annual average air quality
levels measured at WAFB, these results indicate laboratory precision as shown:
CO + 0.046 ppm, or + 23.5 percent
CH4 + 0.016 ppm, or + 0.98 percent
THC (as methane) + 0.016 ppm, or + 0.93 percent
NMCH (HC corrected
for methane)
derived + 0.023 ppm, or + 17.7 percent
These precision estimates apply at the 95 percent confidence level, and they
are referenced to the annual average pollutant concentrations measured at
WAFB.
The persistent low concentrations measured in the WAFB project tested the
state of the art of the air quality analyzers and calibration techniques used.
Most continuous air quality instruments were developed to operate in urban
environments for enforcement purposes or to record ambient concentrations that
are midrange or higher. Concentration levels of CO, NO/NOX, and THC at WAFB
were consistently below national norms for urban environments; therefore the
sensor responses as related to signal-to-noise ratio and lower limits of
detection had to be determined prior to data processing. Analyzer
36
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concentration and nephelometer values were examined to determine if they were
representative of instrument and calibration performance. This was difficult
because very little monitoring of the type needed to evaluate models had been
conducted at the low concentrations of the Williams AFB area. To screen data
from the monitoring network, criteria were used from related experience,
manufacturers' specifications, and calibration and measurement experience from
the five monitoring stations.
Measurement Precision and Accuracy for WAFB Data Base
A summary of 12-month annual average concentration values and measurement
standard deviations for the WAFB data base is given in Table 9. These values
were determined directly from the data base, and they were utilized to
estimate the accuracy limits for the air quality analyzers used at WAFB.
TABLE 9. SUMMARY OF AIR QUALITY PARAMETERS AT WAFB
12-Month Annual Average and Standard Deviation of Measurement
Parameter
CO (ppb)
SDa
NMHC (ppb)
SDa
THC (ppm)
SDa
CH4 (ppm)
SDa
NOX (ppb)
SD
NO (ppb)
SD
b ,. (1(T4 nT1)
scat x
SDb
1
141
90
82
100
1.66
0.07
1.61
0.07
11.0
10.0b
3.0
io.ob
0.55
0.18
S T
2
167
120
137
160
1.70
0.05
1.62
0.15
12.0
10.0b
3.0
io.ob
0.60
0.18
A T I 0 N
3
121
110
106
122
1.67
0.07
1.60
0.10
13.0
10.0b
3.0
10.0b
0.61
0.18
4
361
100
225
146
1.88
0.08
1.67
0.12
20.0
17. Oa
6.0
14. Oa
0.58
0.18
5
195
100
99
78
1.72
0.05
1.66
0.06
12.0
10. Ob
4.0
10. Ob
0.58
0.18
aStandard deviation estimated from calibration data
Standard deviation estimated from manufacturers' specifications
37
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The standard deviations for 12 months of calibration data (daily checks
and biweekly calibration adjustments) have been combined with precision data
to estimate measurement accuracy. Estimates of multiple-station precision
have been developed by averaging the squares of the standard deviations shown
in Table 9, assuming normal distribution of data away from the mean span
concentration. However, statistical tests to choose units that best
approximate the Gaussian normal distribution of the calibration data have not
been performed. Should precision estimates be needed for time periods shorter
than 12 months, a station-to-station comparison of hourly pollutant averages
is recommended using calibration data from Appendix G for the specific period
of interest.
The accuracy of instrumental measurement has been estimated through the
traceability of calibration materials (secondary standards used at WAFB) to
primary standards listed in Appendix G. Analyzer calibration was performed at
only one (span) point. Therefore, analyzer linearity was determined only
through manufacturer's procedures, and precision data derived from the
calibration data should not be used indiscriminately. Estimates of
measurement accuracy derived from instrument standard deviations do not
include sampling variability that can result from manifold (probe) effects nor
do they include measurement bias that can result from station orientation or
wind direction.
Based upon the calibration data recorded in Appendix G, the following
estimates were derived for calibration gas accuracy as determined by
comparison of the WAFB trailer gas cylinders (calibration standards) to known
reference materials (National Bureau of Standards (NBS) traceable cylinder
gases maintained in Las Vegas and at NSI laboratories at Research Triangle
Park, NC):
CO 3.00 + 0.46 ppm
CH4 3.00 + 0.12 ppm
NO 0.42 + 0.042 ppm
These estimates reflect a range of two standard deviations at the 95 percent
confidence level, and they assume that the primary standards are within + 0.04
ppm of the "true" concentration (traceable to NBS).
Estimates of the calibration bias were prepared by determining the
percentage deviation of the stated calibration values from the "true" values.
This percentage deviation was then multiplied by the annual average pollutant
concentration to yield an estimate of the calibration bias. This procedure
relies on the assumption that the same percentage calibration errors apply at
both the span gas concentration and the annual average measured value. Since
no multipoint calibrations were performed at WAFB, this assumption cannot be
supported rigorously.
Using these estimates of calibration bias and the precision standard
deviations given in Table 9, estimates were prepared for the overall
measurement bias (accuracy) encountered at WAFB. Station-to-station variation
38
-------
was averaged by "pooling" the individual station precision standard deviations
using:
n
where SDn = individual station precision standard deviation and
n = 1, 2, 3, 4, 5.
These "pooled" precision estimates were then combined with the calibration
bias to yield an estimate of overall analyzer bias (accuracy) using the
following relationship:
overall bias = -./ (pooled precision)*+ (calibration bias)z
Since THC and NMHC (hydrocarbons corrected for methane) were determined as
methane, the calculation for overall bias for these parameters assumes that
their calibration bias is the same as that for methane. This assumption
naturally disregards any consideration of the conversion efficiency of the
Beckman 6800, and it implicitly assumes that all nonmethane hydrocarbon
species present at WAFB were converted to and measured as methane. The
Beckman 6800 is discussed further in this section.
The following chart summarizes the results obtained from previously
described precision and accuracy calculations (all values are given in ppm
units):
PARAMETER POOLED PRECISION CALIBRATION BIAS OVERALL BIAS
CO 0.1045 0.03 0.109
CH4 0.1053 0.025 0.108
THC 0.0661 0.023 0.07
NO 0.0109 0.0004 0.0109
NOX 0.0117 0.0014 0.0118
Measurement accuracy limits were estimated by dividing the overall bias by the
geometric average of the annual average concentrations shown in Table 9. This
procedure yielded the following results for measurement accuracy limits:
CO + 55 percent
CH4 + 6.6 percent
THC + 4.1 percent
NO _+ 287 percent
NOX Hh 109 percent
Since no calibration was performed with a hydrocarbon standard that did
not contain methane, the accuracy limits for NMHC measurement (difference
between THC and CH4 values) may be estimated by root mean square addition of
39
-------
the overall bias results for CIfy and THC. This results in an estimated
overall bias of 0.129 ppm and accuracy limits of + 99.4 percent for the NMHC
values reported from this study.
Similarly, the accuracy limits for N0£ measurement (difference between
NOX and NO values) may be estimated by root mean square addition of the
overall bias results for NOX and NO. This results in an estimated overall
bias for N02 of 16.1 ppb (0.0161 ppm). When compared to the annual average
NOx concentration of 10.8 pb, this leads to an estimated N02 accuracy
limit of + 149 percent.
Repeatability Data for Beckman 6800 Analyzers
Although multipoint calibration and external performance audits were not
conducted on the continuous analyzers used at WAFB, an extensive body of
quality control data was recorded from daily zero and span checks and biweekly
calibration checks and adjustments. These 4data have been evaluated to provide
a measure of analyzer precision (repeatability). This information becomes
significant because annual average pollutant concentrations measured at WAFB
were well below national standards and were, in many cases, at or near the
analyzer threshold sensitivity. The following material is presented to
support previous estimates of instrumental measurement accuracy and to
document the actual performance of the Beckman 6800 analyzers at low pollutant
concentration levels.
The Beckman 6800 multicomponent CO/CIty/THC gas chromatograph is
essentially three instruments in one integrated unit using flame ionization
detection to measure each component as methane. Separate electronics for each
component amplify the air quality signal transmitted to the data acquisition
system. Each amplifier requires both electronic and chemical fine tuning in
order to provide calibrated output. (See Appendix D for detailed calibration
procedures.)
The Beckman 6800 analyzers were operated on the 0-10 ppm concentration
range. Cylinder gas methane standards were used to check the calibration of
the CH4 and THC components when daily zero and span checks were performed.
Standards with CH4 concentrations at midrange and lower were selected for
span gasses since analyzers normally measured background and low
concentrations of both CO and THC.
The degree of control exercised to monitor span drift of the Beckman 6800
is illustrated in Figure 12. This control chart, for October 1976 at station
3, shows unadjusted span drift and calibration changes as monitored through
the daily checks. The secondary standard concentration in use at station 3
during this period was 4.98 ppm for CO and 5.11 ppm for CH4.
Acceptable span drift limits had been set at + 5 percent of full scale (or
0.5 ppm) for any 24-hour period (Appendix C). Data presented in Figure 12
indicate that the analyzer was within acceptable limits for most of October*
However, span drift recorded during the check on October 25 resulted in
station calibration adjustments.
40
-------
5.6-
O
i
4.8-
§
2
3
2
l
2
2
V*
E
o.
o.
u>
o
p
c
o
Q.
CO
Q)
IO
C
o
Q.
Cfl
tt)
CC
|
5.6-
o
o
0
4.8-
I 234567
|
8
i i i i i i i i r i i r i i i i i i i i i i i r
9 10 II 12 13 14 15 16 17 18 19 2021 22 23 24 25 26 2728 29 30 31 32
OCTOBER 1976
Figure 12. October 1976 control chart for the Beckman 6800
analyzer at station 3.
The pooled estimate of precision for CO measurement is expressed as two
times the pooled standard deviation derived from data in Table 9. Multiple
station analyzer precision for CO (at the 95 percent confidence level) is
estimated at 2(0.1045) ppm, or 0.209 ppm. An EPA summary [17] of audit
performance for Beckman 6800 CO measurement at a level of 3.43 ppm reported a
mean measurement of 3.57 ppm with a standard deviation of 0.62 ppm. The WAFB
CO measurements have better precision by comparison because daily zero and
span check information was maintained as a control on instrument performance.
41
-------
Data from Table 9 were used to derive an estimate for measurement
precision of NMHC (hydrocarbons corrected for methane), which was recorded as
the difference between THC and CH4 concentrations. Standard deviation data
from both THC and Clfy calibration spans were combined to derive a measure of
NMHC precision, assuming that each channel's standard deviation was due to
independent sources of variation:
= J
= ?
: + (0.1053)'
0.124 ppm
Measurement precision for NMHC is then estimated at two times the standard
deviation (at the 95 percent confidence level), or approximately 0.25 ppm.
Measurement Precision for NO/NOX
Acceptable limits for NO analyzer performance were set at + 5 percent of
full scale (+ 0.01 ppm) prior to the start of monitoring, in conformance with
manufacturer's sensitivity specifications. Tests for acceptable quality
control were made with control charts for NO and NOX such as those presented
in Figure 13 for station 5 during April 1977. Span value variation during
this period is estimated at 0.004 ppm. The data presented in Figure 13 show
that station 5 was within tolerance for April and document corrective action
taken to correct trends toward out-of-tolerance operation.
Zero drift for the NO analyzer at station 4 varied from 1 to 5 ppb.
Analyzer precision at station 4 for the 13 months of operation is estimated at
0.034 ppm for NOX at the 95 percent confidence level (two times the
measurement standard deviation shown in Table 9) exceed the annual average NO
concentrations by 2.5 to 3 times at all five stations. This has led to
placement of unusually large accuracy limits (+ 287 percent) on the NO values
reported.
The eight secondary NO calibration standards used at WAFB were cross-
compared to an NBS NO standard cylinder in February 1977 (Appendix G).
Nominal concentration data supplied by the vendor was compared to the NBS
value, and a calibration bias was obtained by pooling the uncertainties of the
secondary standards with those for the NBS material through cross-comparison.
The calibration bias for NO is estimated at + 10 percent of the nominal 0.42
ppm secondary standard concentrations.
Measurement Accuracy Limits for Scattering Coefficient
As part of the daily station zero and span checks, the integrating
nephelometers were checked for response to filtered pure air and internal
"calibrate" reading (a measure of deviation in the instrument optical signal
path). During calibration, both zero air and Freon 12 were introduced to the
instrument, and appropriate adjustments were made to bring the instrument
response to 0.23 (10~*)m~l and 3.6 (10~^)m~-'-, the accepted bwcat values for
clean air (at sea level) and for Freon 12, respectively. No correction was
made to account for the altitude of WAFB, 422 m above sea level.
42
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E
Q.
Q.
3.50-
3.00
2.50-
2.00-
1.50-
1.00-
.50-
K
CO
u
t t
z
o
EC
ffl
z
o
u
z
o
IT
at
I I I
I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 2021 222324252627282930 31 32
APRIL 1977
Figure 13. April 1977 NO/NOX control chart for station 5.
43
-------
As a result of the daily zero and span check and calibration procedures,
performance data were recorded for unadjusted response to clean air and for
adjusted response to clean air and Freon 12 (span). Since no values were
recorded for unadjusted span response, the instrument span drift cannot be
determined. However, zero drift and the variation in adjusted response values
can be used to calculate a measure of instrument precision based on assumed
true bscat values for the zero and span gases 0.23 (10~4)m~l) and 3.6
(10~4)m~I, respectively. These calculations were performed for station 1
for a random sample of five months and resulted in the following:
Standard deviation of instrument span
response (adjusted) 0.12 (10~4)m~l
Standard deviation of instrument zero
response (adjusted) 0.033 (10~4)m~1
Standard deviation of unadjusted zero
response 1.20 (lO"4^"1
The standard deviation for adjusted zero and span variation may be pooled
to yield an estimate of the calibration bias as follows:
calibration bias =
1/(0.12) + (0.033H
V 0.124 (lO-4^"1
Since no record was made for unadjusted span response, the variation in
unadjusted zerp response must be used as a measure of the instrumental
precision. This is not a bad assumption since the annual average bscat
value at station 1 was 0.55 (10~4)m~^ (Table 9), which is very close to
the instrument zero of 0.23 (10~4)m~^. Therefore, when this precision
standard deviation is combined with the calibration bias, an overall
measurement bias for bscat is determined to be:
overall bias = -«/(0.124)2 = (0.20)^ (10~4)m~J
0.235
This overall bias results in an estimate for measurement accuracy limits of
+ 42.7 percent, based on the annual average concentration value.
Research has shown that a correlation exists between scattering
coefficient and mass concentration for atmospheric particulates. In cases
where local atmospheric aerosol can be characterized in terms of particle
size, number, and mass distribution, nephelometer bscat values can be
related to aerosol mass concentration, provided care is exercised in extending
the scattering coefficient over time and space. Urban ambient aerosols
require extensive study in order to characterize their physiochemical light
scattering properties and to relate them to a bscat measurement.
A four-day special study was conducted at WAFB to characterize the local
ambient aerosol. However, analyses were performed only on particles in size
44
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ranges greater than 2 micrometers (urn) in diameter, and no consistent
relationship was established to the nephelometer bscat values, where light
scattering is recorded for particles in the 0.5 to 1.5 urn size range. A
complete report on this special study may be found in an Illinois Institute of
Technology Research Institute (IITRI) publication [22].
By assuming the existence of an average size distribution that remained
constant during the monitoring period, it is possible to estimate a
relationship between mass concentration and light scattering measurements made
at WAFB. Tomback [27] presents details of a correlation established by
Charleson and Ahlquist which states that, for cases where particle size
distribution and specific gravity remain constant with time, the following
approximate proportionality applies between mass concentration (in grams per
cubic meter (g/m3) and bscat (in m~l):
+0.45
mass concentration = 0.45 b«. ,,-,<-
-0.22 scat
Based upon this relationship, mass concentration (in yg/m^) and bscat (in
^"V"1) may be related by:
, +45 _, _
mass concentration (ng/nr5) = 45 bscat (10 ^m A)
Using this mechanism, the annual average bscat recorded at station 1 0.55
(10~^)m~l translates into an estimated mass concentration of
24. 75+?4'?5 jig/m3> an extremely low value in comparison to observed urban
values and the primary National Ambient Air Quality Standard (NAAQS) of 160
4.4 REPRESENTATIVE METEOROLOGICAL CONDITIONS
The representativeness of the meteorological data collected at WAFB is
important to the definition of the accuracy limits of AQAM and the
interpretation of air quality data in terms of evaluating the impact of
airbase operations on air quality. The data set collected at WAFB meets the
minimum monitoring requirement of one year commonly imposed to ensure that
monitoring occurs during all representative wind conditions. However, five
years of representative meteorological data are normally preferred to minimize
year-to-year meteorological variations. The representativeness of the WAFB
data base was tested by summarizing 12 months of data for wind direction and
speed for the five monitoring sites and then comparing these data to the
historical wind rose (see Section 1.3 and Figure 3). Data acquired at WAFB
appears to be representative of typical annual meteorological conditions.
Meteorological data were assembled into frequency distributions according
to WS and 16 classes of WD (in increments of 22.5°) for the five stations.
Figures 14 through 18 present WS and WD in the form of wind-rose diagrams.
45
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HflFB TROILER 1 JULY 76 TO JUNE 77
4.6 2-9 2'6
8-5
7.6
2.3
2.6
0.9
5.6
4.1
3-5
7.9
6.4
12.8
0.00 5.00 10.00 15.00 20.00
PERCENT OCCURRENCE
0-1 1-1 f-S S - Of* I
SPEED CLOSSES (UPS)
f
Figure 14. Annual wind rose at station 1, WAFB, from June 1976 to June 1977.
HflFB TRfllLER 2 JULY 76 THRU JUNE 77
5'4 . 3-D 2.2
8.4
7.3
2.0
2-6
L4.0
0.1
5.7
4.4
3-6
7.3
6.0
14.5
0-00 5.00 10.00 IS.00 20.00
PERCENT OCCURRENCE
i ir FH
o-i i-» t-t «r» Snn
SP£EO CLflSSES (MPS)
Figure 15. Annual wind rose at station 2, WAFB, from June 1976 to June 1977.
46
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MRFB TRRILER 3 JULY 76 THRU JUNE 77
5.7
3.2
2.2
7.7
6.9
2.7
.6
.9
5-5
4-8
8-7
14.7
0.00 5.00 10.00 15.00 20.00
PERCENT OCCURRENCE
o-i i -> >-5 s-t ont »
SPEED CLPSSES (UPS)
N
?
Figure 16. Annual wind rose at station 3, WAFB, from June 1976 to June 1977.
WRFB TRfllLER 4 JULY 76 THRU JUNE 77
12.8
5.8
3.1
2-0
1.8
2.5
6.9
4.5
3.4
f
O-I I-S 1-C
SPEED CLPSSES (UPS)
Figure 17. Annual wind rose at station 4, WAFB, from June 1976 to June 1977.
0.00 5-00 10.00 15.00 20.00
PERCENT OCCURRENCE
47
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HBFB TRBILER 5 JULt 76 THRU JUNE 77
6.0
0.00 5-00 10.00 15.00 20.00
PERCENT OCCURRENCE
SPEED CLRSSES (UPS I
Figure 18. Annual wind rose at station 5, WAFB, from June 1976 to June 1977.
These frequency distributions of wind vector quantities provide information on
the influence of wind on WAFB air quality. Visual inspection of hourly WS and
WD averages plotted by the month (see Appendix h) shows a high repeatability
among wind directions and speeds for stations 1, 2, 3 and 5. Visual
inspection of the wind rose for each monitoring station shows a high degree of
reproducibility between stations. More detailed analysis by Argonne National
Laboratories has shown this to be true for monitoring stations 1, 2, 3 and 5
[14].
The direction and persistence of direction for wind at monitoring stations
1, 2, 3 and 5 (as seen in Figures 14 through 18) compare closely with the
historical wind rose given in Figure 3. Station 4, located near Building 16
of WAFB and a complex of other base buildings (see Figure 4), exhibited a
similar pattern to that of the other stations, although it did show a
difference from the other stations in both WD and WS. WD is about 22.5° more
from the southeast, and WS from station 4 shows a higher percentage of calms
(WS less than 1 m/s). Station 4 WD and WS data appear to be influenced by
nearby buildings in contrast to the other stations, which were located
relatively free from obstructions to wind flow. The WAFB historical wind rose
given in Figure 3 indicates a higher percentage of calm conditions. This may
be attributed to the fact that the trailer wind speed sensors had a lower
starting threshold than the WAFB anemometer.
48
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Wind data in the tabular summaries were analyzed to define the
relationship between WD and time of day. Examination of wind azimuth from
these summaries (Figures H-l to H-91, Appendix H) shows the east-southeast and
west diurnal repeatability. During a high percentage of time, wind was light
and from an easterly direction. By 1,000 hours, the wind began to veer to a
westerly direction for the afternoon. By late afternoon wind was again light
and variable in direction, with airflow typically veering clockwise to an
east-southeast direction by evening. This wind direction persisted until
sunrise. These observations are summarized in Table 10. About 50 percent of
the time, the air motion was from lightly populated areas over a 95° sector to
the east and southeast of WAFB. Winds came from the west or northwest only
about 30 percent of the time.
TABLE 10. WIND DIRECTION AND TIME OF DAY
Duration
(hours)
12
8
5
2
Wind Direction
ESE
SE to W
W
Variable
Time
2000-0800
0800-1300
1300-1800
1800-2000
4.5 OBSERVATIONS BASED ON ANNUAL AVERAGES
Cumulative Frequency Distributions
Hourly averages for CO, NMHC, NOX, and nephelometer bscat were pooled
and divided into intervals of range for concentration and scattering
coefficient according to an estimated increment of resolution of each
instrument. Preliminary estimates of instrument measurement precision were
used to select the concentration range classes presented in the log
probability distributions. The cumulative frequency distributions for the
12-month period show a lognormal or near-lognormal distribution (Appendix K).
The concentration ranges observed at WAFB were narrow in comparison to normal
urban ranges.
The preceding discussion on instrument precision and bias can be applied
to set limits on the usefulness of data shown in these frequency
distributions. For example, single instrument precision estimates from all
stations for CO imply that increments of detection are about 0.21 ppm on the
average. Therefore, concentration changes less than 0.21 ppm at a single
49
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station should not be considered significant. When using data from stations
1, 2, 3 and 5 for purposes of interstation comparison, the estimate of
precision or instrument uncertainty os 0.3 ppm. Therefore a difference in
concentrations of 0.3 ppm between stations is considered significant at the 95
percent confidence level.
Total relative variability between sites can be estimated by assuming
lognormal distribution of the data shown in Appendix L for July 1976 through
June 1977. The geometric mean and standard deviation were determined
graphically from these figures, and these are shown in Table 11. The
frequency distributions given in Appendix K also show characteristics useful
in diagnostic judgment of data quality. For example, CO distributions show
the greatest difference in shape between 150 and 200 pb probably the result
of nonlinear detector behavior at each station for these concentration levels.
TABLE 11. 12-MONTH GEOMETRIC MEAN CONCENTRATION AND GEOMETRIC
STANDARD DEVIATION FOR WAFB (July 1976 through June 1977)
Station
1
2
3
4
5
NOV
X*
8.0
8.8
9.3
14.0
8.5
(ppb)
s**
4.3
4.1
4.3
8.0
4.5
NMHC
X
60
130
88
175
78
(ppb)
s
40
84
62
97
44
CO
X
100
120
80
250
130
(ppb)
s
43
46
40
160
45
NEPH
X
0.5
0.5
0.5
0.5
0.45
-4 -1
(10 m )
s
0.24
0.25
0.21
0.24
0.28
* x = 12-month geometric mean concentration
** s = Geometric mean standard deviation
Wind Direction and Air Quality at the Monitoring Stations
Diurnal persistence of wind for the two dominant directions and periods of
calm conditions (winds less than 1 m/s) were used to sort hourly averages to
observe major features of the data. Subgroups of hourly data were averaged
for all monitoring stations and are presented in Tables 12 through 16.
The maximum and average pollutant concentrations as a function of calm,
east-southeast and westerly wind directions can be used to identify wind
conditions that produce highest concentration. Average concentrations for CO,
NMHC, and NOX are highest at all stations when winds are calm (less
50
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TABLE 12. STATION 1 AVERAGE
VALUES FOR JULY 1976 THROUGH JUNE 1977
NO (ppm)
NOjj (ppm)
CH4 (ppm)
THC (ppm)
CO (ppm)
bscat*
WS (m/s)
NMHC (ppm)
. irtri
TABLE
NO (ppm)
NOX (ppm)
CH4 (ppm)
THC (ppm)
CO (ppm)
bscat*
WS (m/s)
NMHC (ppm)
West Sector
236.25° to 56.25°
Wind Points 12-3
Maximum Average
.0601 .0030
.0768 .0101
3.1841 1.6000
3.2030 1.6642
2.0167 .1433
6.8138 .5050
12.4373 3.0943
1.1521 .0822
13. STATION 2 AVERAGE
West Sector
236.25° to 56.25°
Wind Points 12-3
Maximum Ave rage
.1603 .0035
.2915 .0122
3.0897 1.6073
4.3471 1.6892
3.8692 .1726
7.4879 .5954
14.3444 3.1525
1.3517 .1407
East Sector
56.25° to 236.25°
Wind Points 4-11
Maximum Average
.0682 .0030
.0700 .0095
3.3387 1.5962
3.8976 1.6392
1.5903 .1248
4.4084 .5065
12.8751 2.8979
.9901 .0705
VALUES FOR JULY 1976
East Sector
56.25° to 236.25°
Wind Points 4-11
Maximum Average
.0654 .0031
.0935 .0110
3.1203 1.6245
4.3279 1.6923
1.5876 .1551
5.5254 .5790
13.8851 3.0115
1.3300 .1297
Calm
Wind Speed < 1 m/s
Direction Ignored
Maximum Average
.0525 .0039
.0826 .0141
2.3493 1.5796
2.2812 1.6549
1.2285 .1866
2.3297 .5879
'.9989 .6414
.6501 .0971
THROUGH JUNE 1977
Calm
Wind Speed < 1 m/s
Direction Ignored
Maximum Average
.0302 .0037
.1067 .0162
2.4224 1.6462
2.5358 1.7536
1.4208 .2286
3.3606 .6784
.9991 .6650
.7980 .1641
* lO'V""1
51
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TABLE 14. STATION 3 AVERAGE VALUES FOR JULY 1976 THROUGH JUNE 1977
NO (ppm)
NOX (ppm)
CH4 (ppm)
THC (ppm)
CO (ppm)
bscat*
WS (m/s)
NMHC (ppm)
* lO'V'1
TABLE
NO (ppm)
NOX (ppm)
CH4 (ppm)
THC (ppm)
CO (ppm)
bscat*
WS (m/s)
NMHC (ppm)
West Sector
236.25° to 56.25°
Wind Points 12-3
Maximum Average
.1332 .0028
.2412 .0134
2.8521 1.5739
5.1778 1.6628
3.6703 .1315
5.3051 .5765
13.9436 3.1515
3.5704 .1077
15. STATION 4 AVERAGE
West Sector
236.25° to 56.25°
Wind Points 12-3
Maximum Ave rage
.1808 .0044
.3267 .0172
3.0752 1.6480
4.6890 1.8023
2.7834 .2716
4.1974 .5250
9.3185 2.2021
3.0747 .1725
East Sector
56.25° to 236.25°
Wind Points 4-11
Maximum Average
.0333 .0027
.1137 .0120
3.7748 1.5930
4.3843 1.6714
1.7990 .1116
6.0275 .6167
13.2470 3.0998
2.0024 .1013
VALUES FOR JULY 1976
East Sector
56.25° to 236.25°
Wind Points 4-11
Maximum Average
.0581 .0058
.1408 .0163
3.8024 1.6286
5.3550 1.8230
3.2887 .3403
5.7665 .5632
8.3377 2.1904
3.4413 .2061
Calm
Wind Speed < 1 m/s
Direction Ignored
Maximum Average
.0371 .0038
.1106 .0171
2.2259 1.6067
2.7936 1.7181
1.2230 .1530
3.2374 .6563
.9970 .6636
1.0099 .1280
THROUGH JUNE 1977
Calm
Wind Speed < 1 m/s
Direction Ignored
Maximum Average
.0969 .0085
.1678 .0291
4.2962 1.7728
7.1507 2.0910
3.9774 .5225
3.4194 .6677
.9997 .6395
4.9516 .3230
52
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TABLE 16. STATION 5 AVERAGE VALUES FOR JULY 1976 THROUGH JUNE 1977
West Sector
236.25° to 56.25°
Wind Points 12-3
East Sector
56.25° to 236.25°
Wind Points 4-11
Calm
Wind Speed < 1 m/s
Direction Ignored
NO (ppm)
NOjj (ppm)
CH4 (ppm)
THC (ppm)
CO (ppm)
bscat*
WS (m/s)
NMHC (ppm)
Maximum
.0594
.1111
3.5836
3.7205
2.0612
4.3448
13.9948
1.7339
Average
.0040
.0131
1.6589
1.7223
.1910
.5950
2.9139
.0969
Maximum
.0315
.0837
3.4403
4.0057
2.1784
4.7254
14.4455
1.2332
Average
.0037
.0100
1.6465
1.7072
.1795
.5466
3.0630
.0923
Maximum
.0648
.1075
2.7673
6.3742
2.1724
4.0209
.9990
3.6069
Average
.0049
.0174
1.6954
1.8207
.3123
.6869
.6448
.1484
than 1 m/s). As noted in the wind roses (Figures 14 through 18), however,
calm periods occur less than 3.5 percent of the time for station 4 and less
than 1.4 percent of the time for stations 1, 2, 3 and 5. Winds from the west
occurred about 30 percent of the time, and averages of hourly data for CO,
NMHC, and NOX were higher for this condition, as opposed to easterly winds,
for all stations except 4. Average CO and NMHC concentrations at station 4
are higher when winds are from the east-southeast (compared to the west
sector), suggesting a persistent source of emissions or transport from that
direction.
Maximum concentrations also generally occurred when winds were from the
west. Exceptions were for station 1 in terms of NC^ and stations 4 and 5 in
terms of hydrocarbons and CO.
A more detailed analysis is required to further identify specific source -
receptor relationships. Cumulative frequency distributions, for example, show
that concentrations of CO exceeding 1 ppm occurred at stations 4 and 5 for
about 20 percent of the time. Concentrations exceeding 1 ppm for NMHC
occurred about 5 percent of the time at station 4 and 1 percent of the time at
station 5. Correlation of these data subsets to wind direction should provide
additional insight to source impact.
53
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On the average, CH4 concentrations at station 1 on Williams AFB were 99
percent of the THC level. CIfy comprised 96 percent of the THC when averages
were selected for winds from the east-southeast. CH4 usually contributes
from 60 to 90 percent of THC concentration in urban atmospheres of North
American latitudes and occurs in concentrations of about 1.25 to 1.5 ppm [14,
20, 21]. Station 4 City was 89 percent of the THC concentration, giving the
characteristic of urban CH4/THC ratio. In the development of atmospheric
geochemical data, CH4 has contributed as much as 95 percent of hydrocarbons
present in desert (little vegetation) regions of the West (Summary Report,
U.S. Department of Interior Oil Shale Leasing Program, C-B Shale Oil Project
[22]). CH4 and THC data at Williams AFB appear to be comparable and
representative of Southwest air quality in general.
Comparison of WAFB Air Quality to National Standards
Carbon Monoxide
Carbon monoxide concentrations (hourly averages) were examined in relation
to the national standards. CO concentrations never exceeded the annual
standard eight-hour average of 9 ppm or the one-hour average of 35 ppm. CO
concentrations greater than 3 ppm occurred on 10 days for the July 1976
through June 1977 monitoring period. The day, time of day, and measured
concentration are shown in Table 17.
TABLE 17. DATE AND TIME CO EXCEEDED 3 PPM
Concentration
Station Date/Hour (ppm)
4
4
4
4
4
4
4
4
4
4
Oct.
Nov.
Nov.
Dec.
Dec.
Dec.
Dec.
Dec.
Jan.
Feb.
r
19,
18,
29,
3,
7,
21,
29,
29,
10,
3,
1976
1976
1976
1976
1976
1976
1976
1976
1977
1977
0800
0800
0800
0800
0800
0800
1800
1800
0800
1000
3.
3.
3.
3.
3.
3.
3.
3.
3.
3.
57
14
93
29
49
98
87
67
15
96
54
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NMHC (Hydrocarbons Corrected for Methane)
Nonmethane hydrocarbon concentrations were examined for the three-hour
period from 6 to 9 a.m. in order to relate measured NMHC concentrations to EPA
guidelines for hydrocarbons corrected for methane that serve as oxidant
precursors. Three-hour averaged concentrations compiled from tabular
summaries of NMHC exceeded the federal guideline of 240 pb 111 times during
the 13-month period. On no occasion during the 6 to 9 a.m. period did NMHC
exceed 1 ppm at any site. During the winter season of 1976, meteorological
conditions resulted in higher measured NMHC concentrations.
Nitrogen Oxides (NOX)
NOX concentrations have not been related to existing N02 standards
since no data processing was performed to estimate N0£ levels as the
difference between NOX and NO measurements. As seen in Table 18, the annual
average concentration for NOX did not exceed the 0.05 ppm annual N02
standard at any monitoring site.
TABLE 18. ANNUAL AVERAGE CONCENTRATIONS FOR ALL STATIONS
JULY 1976 THROUGH JUNE 1977
ppm
Station
NO
NO.
x
CH4
THC
CO
NEPH*
NMHC
1
2
4
3
5
.0031
.0033
.0060
.0028
.0039
.0108
.0119
.0197
.0129
.0118
1.6069
1.6210
1.6687
1.5882
1.6555
1.6552
1.6984
1.8813
1.6718
1.7231
.1411
.1672
.3609
.1213
.1958
.5468
.6017
.5790
.6061
.5753
.0822
.1374
.2252
.1056
.0994
* units of
4.6 ASSESSMENT OF IMPACT ON AIR QUALITY AT THE MONITORING SITES
The direction and persistence of direction for the wind at monitoring
stations 1, 2, 3 and 5 was used as a basis for describing base air quality.
The high percentage of time that this diurnal pattern is true for WAFB also
suggests that a development of average background air quality would be
representative for the area around the base.
Annual averages taken from tabular summaries for all stations are shown in
Table 18 for the period July 1976 through June 1977. Station 4 stands out as
55
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the location where assessment of air quality impact may be performed in terms
of concentrations as a result of WAFB activity as opposed to local background
conditions.
The diurnal persistence of wind direction was used as a basis to observe
major features of the annual averages of data shown in the cumulative
frequency distributions. Concentrations of NOX, NMHC, and CO (when plotted
for one day) were used to observe sources of emissions that may be located in
areas surrounding WAFB. Nontypical meteorological conditions were usually
associated with higher concentrations of NOX, NMHC, and CO. Examples of
episodes and higher-than-normal concentrations are shown in Appendix H,
Figures H-92 through H-134. Specific examples are also shown for September 26
and December 29, 1976, and for January 27 and May 11, 1977.
Airbase air quality in contrast to background concentrations was developed
through the rationale that average conditions and wind directions from all
points of the compass should be considered ,for the description to be
representative. Station 1 averages from east-southeast conditions are
designated as background air quality. Comparison was done by averaging the
annual average concentration for stations 1 and 5 to characterize base air
quality. These averages contain contributions from airbase operations;
however, they are the least impacted by base operations because of WD under
typical east-southeast wind conditions. The approach was further justified on
the basis that they are located at some distance from station 4, which may be
considered as the location where the impact of all activity (including flight
operations) may be highest during typical wind conditions. Slight impact on
concentrations at stations 1 and 5 was detected for short periods of time (see
Appendix H, Figures H-92 to H-101). Station 1 averages were summarized
between the hours of 2000 in the evening and 0800 in the morning when wind was
from the east-southeast. Background and base air quality concentrations
developed from this approach are shown in Table 19.
TABLE 19. ANNUAL AVERAGE AIR QUALITY CONCENTRATIONS AT WAFB
Station
NO*
(ppb)
NOX
(ppb)
CH4
(ppm)
THC
(ppm)
CO NEPH*
(ppm)
NMHCt
(ppb)
- Background-
It 3.1 10.8 1.61 1.66 140 0.52 62
- Airbase (Including Background)
1 & 5 3.4 11.3 1.64 1.69 169 0.57 91
* bscat ls in 10 ^m * units
t Concentrations from station 1 were averaged for the period July 1976 through
June 1977 between 2000 and 0800 (see Table 18).
56
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As can be seen from Table 19, the differences between the annual average
concentrations selected to produce the lowest levels are insignificant in
relation to the annual average for all periods of time at stations 1 and 5.
Station 1 was least impacted by airport or aircraft-related activity. On an
annual basis, the average of stations 1 and 5 is representative of the
background, or base, air quality.
A comparison of station 1 and 5 average concentrations for NOX, NMHC,
and CO to those for station 4 is presented in Table 20.
TABLE 20. COMPARISON OF SELECTED'
ANNUAL AVERAGE CONCENTRATIONS
Station
Annual Average Concentrations (ppb)
NCK,
NMHC
CO
1 & 5
4
11.0
20.0
91.0
225.0
169
361
Difference
134
192
The difference in CO levels between station 4 and the average of station 1
and 5 was judged to be significant at the 95 percent confidence level. The
differences for NOX and NMHC were not significant at the 95 percent
comfidence level.
During periods when the prevailing wind is from the east-southeast,
station 1 average concentrations are not directly related to WAFB activities.
This condition occurred for approximately 50 percent of the 13^month period.
The percentage of time that measured air quality levels exceed those at
station 1 is a good indication of the impact of airport or aircraft activity
on base air quality as measured at station 4. Table 21 presents a comparison
of annual average concentrations as measured at stations 1 and 4 during
periods of east-southeast prevailing wind conditions. Also presented is a
TABLE 21. COMPARISON OF DATA FROM STATIONS 1 AND 4
DURING EAST-SOUTHEAST WIND CONDITIONS
Station
NOX
NMHC
CO
1
4
11
20
83
225
141
361
Impact
Indicator
142
220
57
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quantitative indicator of the difference between the station averages for the
purpose of determining observed air quality impact, if any.
From inspection of the data in Table 21, it is apparent that there is an
impact on base air quality during periods of east-southeast wind movement.
However, without specific extraction of selected station data for discrete
time periods and correlation to airbase operations records, no assessment can
be made on the impact of aircraft or airbase activities and no determination
can be made of potential emissions sources that have impacted the existing
base air quality at station 4. Such analyses are possible with the existing
data base, but they will be expensive in terms of labor and computer
manipulation of tabulated measurement data. The success of such analyses will
depend directly upon the degree to which the data search objective is
specified prior to the beginning of any analysis.
Using existing annual average concentration data for stations 1 and 4, the
following observations can be made on generalized air quality impact:
For 21 percent of the monitoring period, there was a significant
difference in CO concentrations as measured by stations 1 and 4 at the
95 percent confidence level.
For 12 percent of the monitoring period, there was a detectable
difference in NMHC concentrations as measured by stations 1 and 4, but
the difference is not significant.
For 6 percent of the monitoring period, there was a difference in NOX
concentrations as measured by stations 1 and 4, but it is not
significant.
Since there are no major emissions sources (other than vehicular) in the
proximity of WAFB, it must be assumed that the impacts noted above are due to
emissions from local vehicular traffic (airbase personnel) or from airbase or
aircraft operational activities.
Impact of air quality at stations 1, 2, 3 and 5 on an average annual basis
is slight, at less than the 95 percent confidence level. There was no impact
of air quality at these stations at the 95 percent level of confidence using
the pooled precision of measurement estimates provided in Section 4.2 above
and the definition of background base air quality.
4.7 RESULTS OF RELATED SPECIAL STUDIES
Several short-term studies sponsored by the USAF were carried out at
Williams AFB and at other locations to measure vertical and horizontal
dispersion of aircraft emissions and to develop empirical data useful in
modeling.
58
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Each of the following studies is summarized briefly in this section:
EPA recommendations on the evaluation of AQAM
Preliminary air quality analysis (1975)
Horizontal wind dispersion parameter investigation
Particle morphology of aerosols collected at WAFB
Remote optical sensing of emissions (ROSE) study
Correlation spectrometer (COSPEC) study
Gas-filtered correlation (GFC) spectrometer study
Scanning laser doppler velocimeter system (SLDVS) investigation
EPA Recommendations on the Evaluation of AQAM
EPA recommended a data analysis procedure for the accuracy definition
being completed by ANL. Meteorological and emission data are critical input
for modeling air quality concentration gradients. Accuracy definition
requires the grouping of data for valid comparison of measured concentrations
to model predictions. Once the data base are collected, valid data grouping
according to real meteorological conditions is necessary to make comparisons.
Several categories were proposed prior to analysis of any WAFB data, including
meteorological categories such as wind direction and speed and atmospheric
stability. It was recommended that two or three categories of mixing height
be chosen in order to evaluate AQAM performance.
A cumulative frequency distribution of calculation error compared to
measured data should be constructed to examine model performance for specific
cases and to provide information on the distribution of over- .and under-
prediction for a specific category. Tests of the model accuracy would then
depend on the user's supporting data analysis in terms of specific categories
of testing. See Appendix B for further discussion of percent error
distribution.
Preliminary Air Quality Analysis (1975)
The ambient air analysis study (mentioned in Section 2) was conducted as a
preliminary guide to the development of the WAFB monitoring operations, and it
provided qualitative information on plume rise and initial jet exhaust plume
pollutant concentration as a function of downwind distance. The static jet
portion of this study was conducted during idle and power engine modes while a
helicopter made downwind passes at altitudes between 3.1 and 42.7 m AGL.
Relative concentrations (based on the averages from all traverses of the
helicopter) were used to determine effective plume rise, which is useful for
verifying vertical dispersion. From these averages it was determined that jet
exhaust plumes were located at 7 m AGL, 50 m downwind; 20 m AGL, 100 m
59
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downwind; 20 m AGL, 150 m downwind; and 21 m AGL, 200 m downwind. The full
report is included in Appendix B.
Horizontal Wind Dispersion Parameter Investigation
The Pasquill stability class dispersion parameters are an important input
to the approach used in AQAM. The purpose of the horizontal wind dispersion
study was to determine how the subjective observation of stability class at
WAFB (i.e., the method of determining stability class from WABAN observations
[23] compared with the measured horizontal dispersion values from propeller
vane wind measurements at each monitoring station.
A wind study was conducted at WAFB during the first week of monitoring,
June 1976, using the R. M. Young Gill propeller vanes. These vanes are light
and have fast time response. The average AGL height for the vanes was 8 m.
Lightweight propeller vanes can effectively measure WS fluctuations in the 1
to 10 m wavelength range. WS fluctuation in.this range is an important
phenomenon in atmosphere diffusion.
From June 1 through 8, 1978, strip-chart recordings of WS and WD were
collected for seven periods of several hours each from all monitoring stations
of the network (see Figure 4). From these records, a shorter period of
homogeneous turbulence (June 4 through 7) was selected for detailed analysis,
when winds were generally light (below 5 m/s). Maximum temperatures were in
the mid 30's (°C) and minimums were in the low 20's (°C), typical of summer
weather in the Phoenix area.
The assumedssimilarity of turbulence readings between the trailers was
tested by examining the strip-chart data using a five-minute averaging time.
In a nighttime case, the values of horizontal dispersion (
-------
nighttime fluctuations were usually more dense as a result of mechanical
turbulence caused by horizontal flow, but the daytime small-scale fluctuations
were larger as a result of thermal turbulence.
Particle Morphology of Aerosols Collected at WAFB
In conjunction with a particle study being conducted in Phoenix in
November 1975, the EPA requested that aerosol samples be collected at WAFB.
Microscopic examination of the collected aerosols by the Illinois Institute of
Technology Research Institute (IITRI) was conducted to determine what
differences, if any, existed between particle types collected at WAFB and
those collected in the Phoenix metropolitan area [18].
Aerosol samples were collected on November 17, 18, 21, 23-24 (overnight),
and 25, 1975, with four samplers located at three different sites at WAFB:
near site 4 at Building 16, at a remote sensing unit near site 2, and at a
transmitter antenna near site 1 which had samplers situated at 1.55 m and 4.5
m AGL. Sampling intervals were chosen to take advantage of known windflow
patterns in the Phoenix valley area.
All samples collected at WAFB were analyzed by optical microscopy. Some
samples were further examined by scanning electron microscopy. Selected
nuclepore filters were also examined by SEM. General observations made during
the examination of each sample are given in an IITRI Report [18].
The particle size distribution data indicate that, on a number basis, the
mean particle diameter at each sampling site was less than 2 inn. In addition
to categorization by size, the particles were also categorized into two basic
types mineral and nonmineral. The mineral category contained various soil
minerals, fly-ash spheres, and higher density particles such as metal
fragments. The nonmineral category included the fine carbonaceous particles,
carbonized flakes, biological particles, and tire rubber particulate. Size
distribution data obtained are presented in Tables 22 and 23 of Appendix B.
Remote Optical Sensing of Emissions Study
Long-path infrared spectroscopic measurements of CO concentrations were
made by the EPA during the period February 10 through 19, 1976, at WAFB to
provide integrated CO concentrations over the path length between two points.
Remote optical sensing of emissions (ROSE) was included as a part of the USAF
investigative program to attempt to overcome the inherent difficulty of
comparing the average value predictions of dispersion models with the
fixed-point values obtained from the five sampling stations. The sites
(optical paths) for the ROSE measurements were chosen to be adjacent to major
WAFB aircraft operations. The infrared light source and receiver units were
equiped with telescopic optics to permit long-path (up to 3 km) measurements.
The measured gas concentrations obtained in this manner are the concentrations
that would be obtained if the gas molecules were uniformly distributed over
the entire optical path length.
A total of 236 individual CO concentration measurements were made during
the seven days of long-path data collection. Highest average CO
61
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concentrations of about 4 ppm were measured along an optical path that
traversed an individual jet plume for an appreciable period of time. Along
other optical paths, most concentrations remained under 1 ppm. A path-
averaged concentration of 3 ppm was measured about 20 m north of five idling
jets at the east end of taxiway 5. Further information on this study may be
found in Appendix B.
Correlation Spectrometer Study
Environmental Measurements, Inc. (EMI), under contract to EPA, performed
six days of measurements from October 20-27, 1976, using the COSPEC
correlation spectrometer. The goal was to document nitrogen dioxide (N02)
pollution flux entering and leaving the base area. Additional data were
gathered on regional pollution levels in the greater Phoenix area and in the
vicinity of the Phoenix (Sky Harbor) Airport. Total sulfur measurements were
also used as indicators of external emissions transport entering the WAFB
area.
Sulfur dioxide (862) and N0£ overhead burdens were measured with the
COSPEC remote sensor from a moving van. Total sulfur (TS) and NOX were
measured at ground level with continuous analyzers. The remote sensing COSPEC
was also mounted on a tripod near the taxiway (site 3) for stationary
measurements of vertical and horizontal profiles of N02« Another task was
to monitor while circumnavigating the base on the perimeter road that circled
the main aircraft operations area. The basic perimeter traverse was 13.5 km
long and required 25 minutes to complete. These measurements around the base
were carried out 25 times in six days. Typical observations for both total
burden and ground-level measurements were that S02 values varied over 40
ppmM while the N02 varied over a 20 ppmM band of values.
Preliminary results were reported as follows [24]:
Ground-level total sulfur at low concentration shows transport of this
type entering WAFB to be limited.
Ground-level NOX variation is associated with vehicular traffic in
the base area and along the perimeter of WAFB.
The stationary COSPEC results suggest a higher relative concentration of
N02 to the northwest of WAFB toward the Phoenix area. A peak concentration
has not been computed. The integrated level was 30 pmM at 2° elevation
north-northwest of WAFB. A detailed report on the study is available in the
EMI report, "Moving Laboratory Survey at Williams Air Force Base" [24].
Further summary information is presented in Appendix B.
Gas-Filtered Correlation Spectrometer Study
Three nondispersive infrared instruments were used at WAFB for long- and
short-path remote sensing measurements [11].
The sensitivity of a GFC spectrometer depends on the correlation between
the structure in the spectrum of the gas species to be measured and that of
62
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the same species in the correlation cell internal to the instrument. This
study is summarized in Appendix B.
Scanning Laser Doppler Velocimeter System Investigation
As part of the overall USAF program, data from a scanning laser Doppler
velocimeter (SLDVS) were to determine the feasibility of using this system to
map the concentration of particulate pollution in the atmosphere around
airports. The system was operated at Kennedy International Airport from
September 1974 through May 1975 for detecting and tracking aircraft wake
vortices during landings on runway 31R. Since the system measures laser
radiation back-scattered by particles in the atmosphere, it was postulated
that the data from the system could be used to determine the concentration of
these particles. The data consisted of tape recordings of digitized spectra
along with time and spatial coordinates as a function of vertical and
horizontal position. Approximately 450 such vertical signal profiles were
prepared from data taken during 50 landings on five separate days in the
spring of 1975. A complete report of this study, including vertical scans has
been prepared by Raytheon Company [25].
A preliminary analysis of the data was performed to determine the
relationship between signal and atmospheric backscatter coefficients and to
evaluate the general quality of the resulting data. This data analysis
indicated that the system was successful in measuring changes in returned
signal strength, based on the repeatability of data from scan to scan.
63
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SECTION 5
CONCLUSIONS AND RECOMMENDATIONS
The collection, processing, and analysis of all continuous air quality and
meteorology data from the WAFB study have been completed. Hourly averaged
monitoring data have been provided to ANL for use in AQAM accuracy definition
analysis, and a preliminary assessment has been made of the observed air
quality impact from WAFB aircraft and airbase operations. In addition, the
results obtained from related special studies have been interpreted to provide
relevant information concerning dispersion a,nd transport of WAFB emissions.
This section summarizes the conclusions reached thus far (in relation to
the major study objectives presented in Section 1) and presents
recommendations for future airport air quality studies (specifically, those to
be conducted at NAS Miramar in San Diego, California). Recommendations
concern station siting, operational constraints, data collection, and analysis
and interpretation of study results.
This report provides a qualitative assessment of the impact of aircraft
emissions on air quality at Williams AFB. This assessment of the impact from
aircraft emissions is defined for the purposes of this study to consist of
observations of actual frequency distributions of concentrations of
aircraft-related pollutants (CO, NOX, reactive hydrocarbons, and
particulates) at monitoring locations known to be subjected to aircraft
emissions. Since the AQAM dispersion model yields predictions for one-hour
average pollutant concentrations, and the second major objective of this study
was to determine the accuracy limits of this model by comparison with
observations, pollutant concentration measurements are reported as frequency
distributions of one-hour averages. To estimate "impact" of emissions,
frequency distributions in areas known to be subjected to emissions have been
compared with frequency distributions observed in areas believed to represent
"background" i.e., areas relatively unaffected by aircraft emissions.
The data are representative of all typical meteorological conditions
around Williams AFB. Data were collected under conditions having the least
potential for impact on air quality, which generally occur in the summer*
Typically, as soon as the sun rises, any emissions from airport or aircraft
operations disperse quickly in the desert climate. This observation is
supported by the highly repetitive nature of this meteorological condition.
Data were also collected during infrequent meteorological conditions that are
conducive to high impact on air quality. In no case, however, did measured
concentrations exceed or approach the national ambient air quality standards.
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5.1 DATA BASE FOR AQAM ACCURACY DEFINITION
A data base consisting of 13 months of continuous air quality monitoring
data has been successfully collected, edited, and converted to hourly average
form for use in comparison to predicted ambient concentrations obtained from
the AQAM formulation. Data recovery was 70 percent over the total period of
monitoring, and the measurements obtained are representative of actual air
quality levels encountered at ground level for the WAFB sites during the
period from June 1976 through June 1977. Measurement accuracy limits have
been determined for this data set based upon the measurement standard
deviation of the data set and the calibration bias as obtained from daily
check and station calibration records.
The ground air quality concentrations encountered at WAFB were often very
low and in many cases approached the measurement sensitivity for the
commercial analyzers used. As a result, the reported measurement accuracy
limits are large in comparison with studies that involve higher pollutant
levels associated with urban areas. Accuracy definition for AQAM, when used
to predict air quality concentrations at WAFB, must account for these low
physical measurement values, and predictions for CO, NOX, and hydrocarbons
must be representative of the low values obtained (on an annual average basis)
at the five monitoring sites. Because of the low concentrations measured,
AQAM accuracy definition will be very sensitive to the emission input data
supplied prior to exercising the model. If any positive or negative bias in
predictions is neglected, the data base collected should compare favorably to
model predictions in the vicinity of the ground sites.
The low concentration values observed from the data base collected at WAFB
indicate that the measurement of aircraft and airbase pollutants should not be
conducted at ground level in locations immediately adjacent to the sources of
emissions. In addition, the selection of actual measurement sensors should be
based upon a preliminary study at the affected facility to determine
background air quality and representative pollution levels at site locations
where emissions are predicted to have measurable impact. Measurement sensor
selection should also take into account the relative importance of NAAQS
compliance data versus concentration data for use in evaluating the output of
predictive dispersion models. The measurement sensitivity requirements for
the latter objective are more stringent than those normally specified for the
former, particularly in cases where observed air quality levels approach
background concentrations.
5.2 ASSESSMENT OF AIR QUALITY IMPACT AT WAFB
Within the limits of measurement accuracy (as estimated in Section 4), the
data reported indicate that, for the specific geographical area and associated
meteorological patterns encountered, WAFB aircraft and airbase emissions did
not have a significant impact on local base air quality levels. Measurements
made during several related special studies indicate a high potential existed
for transport and diffusion of aircraft emissions away from the airbase as a
result of the buoyant plume rise normally associated with emissions that take
place at elevated temperatures (such as in jet exhaust).
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Continuous air quality measurements were made at ground level under all
representative meteorological conditions. Cumulative frequency distributions
of hourly average concentrations for CO, NOx, City and NMHC were explained.
These data are representative of WAFB air quality on an annual basis at ground
level. The volume available for pollutant dispersion (mixing volume),
atmospheric stability, and other meteorological factors tend to reduce the
potential for high pollutant concentrations at ground level in the vicinity of
WAFB emissions.
At no time did measured air quality levels at WAFB exceed national
standards. In many cases, measured pollutant concentrations approached
background air quality levels for the WAFB geographical area. As a result,
the determination of air quality impact from WAFB emissions was very difficult
and relied heavily upon comparisons between pollutant concentrations at
different stations. However, between-station variations must be carefully
considered in light of the low pollutant levels measured, the resulting large
percentage limits for measurement accuracy, and the local airbase
meteorological and terrain factors that may have influenced individual station
measurements at ground level.
The same data base that was collected for accuracy definitions of AQAM was
reviewed to assess the impact of emissions on air quality at Williams AFB.
Sorting the data as a function of wind direction and speed has not shown any
major feature that indicates that WAFB emissions had a measurable impact on
base air quality. Wind roses from the five monitoring sites show two dominant
wind directions that are highly repeatable from day to day. Stagnant
conditions represented about 2 percent of the time for the monitoring period.
Station 4, located where base vehicular emission sources were evident, is
clearly indicative of airport-related activity. Airflow in and around this
site was clearly affected by the proximity and height of nearby buildings.
Wind speed at this site was lower, as evidenced by a higher percentage of calm
(< 1 m/s) conditions, and parcels of air containing airbase emissions may have
accumulated there. Highest pollutant concentrations were recorded at this
monitoring site for the highest percentage of time. Typical meteorological
conditions at WAFB were characterized by higher morning concentrations for
each base operating day. Higher concentrations were evident in the afternoon
as well, when personnel departed working areas, although this effect was less
pronounced on the average.
When wind was from the east-southeast, station 4 air quality was
influenced by a persistent emission source downwind from sites 1 and 3.
Concentrations of CO and NMHC were higher from this direction than from the
westerly direction, on an annual basis. Under stagnant wind conditions (high
pollution potential), station 4 hourly averages of CO never exceeded 5 ppm
and, on the average, were less than half the level of the national standard
for CO.
The discernible features of the WAFB data set reported here are not
sufficient by themselves to allow a vigorous determination of the air quality
impact from WAFB emissions. Rigorous statistical tests must be applied to the
data base to determine the significance of between-station variations in view
of the low recorded measurement values. Without these tests, it is not
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possible to state conclusively that an observed measurement variation is
solely the result of the presence of an emission source. Similarly, it is not
possible to identify or characterize any specific emission source without
tests, such as multiple regression analysis, that incorporate all known
independent sources of influence on air quality (including emissions, local
meteorology, instrumental precision and accuracy, and terrain features).
Faced with this situation, the use of a properly validated mathematical model
becomes more desirable and practical.
5.3 RELATED SPECIAL STUDIES
To supplement the continuous air quality data collected from the network
of five ground stations, a series of related special studies was conducted at
WAFB. These studies included the collection of air quality and meteorology
information using specially developed research techniques and instrumentation.
While the special study results (presented in detail in Section 4) did not
conclusively demonstrate that WAFB emissions were being transported outside
the region monitored by the ground stations, they did indicate that a
potential existed for dispersion of hot exhaust emissions, and they
demonstrated the feasibility of using several monitoring techniques that were
still in the developmental stage. In addition, the special studies pointed
out the need for additional air quality measurements (above ground level) on
future airport studies, and they provided qualitative indicators for the
suspected mechanisms of emission transport and dispersion.
Studies that showed particular promise for the measurement of indirect
sources in general, and line sources (highways, runways, etc.) in particular,
involved long-path absorption principles. These methods of sampling air
quality provided integrated measurements between two points, one of which was
the energy source and the other the point at which absorption spectra were
recorded. Problems encountered with these techniques include limited
sensitivity and resolution in the concentration range of interest and lack of
acceptable methods of calibration that can be related to other data.
Micrometeorology is perhaps the most important empirical data input to a
model in terms of defining the representative accuracy of predictions.
Boundary-layer profile research, together with advanced techniques of
characterizing vertical dispersion, show promise in collecting airport
emissions dispersion data. The helicopter platform provides a feasible way to
develop quantitative emissions dispersion data at airports. The correlation
spectrometer, as an upward-looking technique together with helicopter
measurements of downwind dispersion data at airports. The correlation
spectrometer, as an upward-looking technique together with helicopter
measurements of downwind dispersion, shows promise of providing data to
characterize the emissions flux and transport from aircraft sources.
Insufficient data were collected to relate mass-loading of particles to
the measured nephelometer parameter bscat. Further analysis is required to
provide mass-per-unit-volume data at Williams AFB on a representative basis as
related to continuous bscat measurements. Data do suggest that the majority
of particle sizes lie outside the size range where scattering is measured by
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the nephelometer. Promising techniques are now available for particle
monitoring in the vicinity of emissions. These are membrane filter sampling
from ground and airborne systems as coordinated with forecasted meteorological
conditions. Analysis may then be conducted to obtain a "fingerprint" of
emissions, which is directly related to the source contributions.
Further review of the results of these special studies is recommended in
order to optimize their potential for airport monitoring at other locations.
Specific conclusions that have been made as a result of current analyses are
presented in the same study order as that in Section 4.
Preliminary Air Quality Analysis
Three experiments were conducted in the preliminary study, and the
distribution and transport of pollutants was inferred by:
A study of pollutant concentration around the airport using grab
samples conducted by ANL
A study to estimate the effects of a single jet sitting in one place by
measuring plume rise with helicopter measurements above ground,
including grab sampling by ANL
The ground-level measurements of concentration range with continuous
air quality monitors
The effect of wind direction on concentration was examined by constructing
pollution roses. This preliminary study appeared to confirm the feasibility
of monitoring to develop one-hour average frequency distributions of air
quality parameters at selected sites in the vicinity of emissions sources at
Williams AFB. It was also felt that the emissions could be more accurately
assessed by comparing air quality frequency distributions in areas with
minimal aircraft emissions to those where aircraft emissions would be highest.
Horizontal Dispersion Study
Horizontal dispersion and fluctuation of wind direction can be used for
comparison with Pasquill stability model parameters. In conclusion, because
of the intense insolation in the Phoenix valley, the lower atmosphere varies
from slightly unstable to extremely unstable throughout the day and into the
night during summer. Pasquill stability classes seem to be low by an average
of two classes. The most unstable case, Class A, is off by a factor of 2 or
3. The nighttime fluctuations were usually more dense because of mechanical
turbulence, but the daytime small-scale fluctuations were larger as a result
of turbulence.
Particle Morphology at Williams AFB
The major components of atmospheric aerosols in terms of mass at WAFB are
minerals indigenous to the soil of the area. Motor vehicle traffic was
partially responsible for resuspension of the soil minerals. Analyses in the
size ranges collected indicated that the vehicles themselves contributed only
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minor concentrations of particulates to the atmosphere. No relationship was
established as characteristic of jet emissions.
Remote Optical Sensing of Emissions
Long-path measurements of CO showed 4 ppm average concentrations along a
670-m path through the plumes of five idling T-38 aircraft between the taxiway
and inside runway. Visual observation of the jet exhausts and the fact that
the highest CO concentrations occurred along this Path A, in contrast to a
path adjacent to the runway, suggested that the jet plumes were rising.
Correlation Spectrometer Study
Results with the most potential for monitoring airport emissions in terms
of NOX were suggested through mobile perimeter measurements and stationary
outward-looking measurements to locate varying concentrations. Peak
concentration of these measurements was not computed; however, the data
suggested that an NOX source exists in the north-northwest direction toward
Phoenix.
In contrast to the ROSE principle of measurement, which has its own energy
source, the COSPEC uses the sun and can obtain a continuous record of oxides
of nitrogen while moving to obtain a map of relative concentration with
location.
Gas-Filtered Correlation Spectrometer Study
These devices were both fixedpoint and long-path monitors. The principle
of measurement is nondispersive infrared absorption, similar to that of the
Federal Reference Method for CO.
The study did not provide data useful for plume rise description. Because
the peak concentration and duration of concentration from jet exhaust is
dependent on WS and WD, the length of time for observations of the plume was
too short for the instrumental configuration used perpendicular to the runway.
Response of the method is slow, and transient concentrations of CO were not
present at instrument height for sufficient periods of time.
Scanning Laser Doppler Velocimeter System Investigation
The scanning laser Doppler velocimeter system (SLDVS) was used to map
particles in wake vortices of aircraft at Kennedy International Airport,
ancillary to the WAFB studies. Based on the repeatability of data from
individual measurements, changes in returned signal strength were detected.
In summary, the principle of using an SLDVS for airport pollution
monitoring of atmospheric backscatter coefficient appears to be feasible. A
reasonable amount of data was obtained and processed with the system at
Kennedy International Airport.
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Summary of Conclusions for Special Studies
Pollutant concentrations measured by the helicopter showed the jet plume
well above the normal height for measuring air quality from ground-level
monitoring stations for example, the jet plume during one test appeared to
be 45 meters AGL at 200 m downwind.
Vertical dispersion was investigated by the static jet study discussed in
Section 2, an SLDVS study, and a Barringer correlation spectrometer (COSPEC)
study. The acoustic sounder study (see Sections 2 and 4 and Appendix F)
provided additional information for vertical dispersion, which was also
investigated through a wind dispersion study, the COSPEC study, and a
gas-filtered correlation (GFC) spectroeter study.
Remote or longpath air quality measurements can be used to measure
buoyant plume rise of aircraft emissions and to estimate total pollutant flux
arising from other sources on the airbase. Remote sensing instrumentation is
also useful in measuring the average pollutant concentration over a given path
for comparison with model calculations.
5.4 RECOMMENDATIONS FOR NAS MIRAMAR STUDIES
Based on experience gained at Williams AFB, four areas of data acquisition
are recommended to monitor emissions and provide data for model evaluation at
NAS Miramar in San Diego, California.
Statistical meteorological studies to develop conclusions about site
locations, numbers of sites, and dominant sources should be implemented.
Micrometeorological data should be acquired to determine horizontal and
vertical dispersion parameters together with stability classifications. These
can be obtained using tethered-balloon sampling platforms and dynamic air
quality measurements using spectrometric principles.
It is recommended that measurement of air quality parameters be conducted
for limited periods of time from fixed monitoring locations. Classification
of meteorological conditions as statistically representative will then permit
a choice of a monitoring interval consistent with the defined monitoring
objectives, whether they be for model input data or impact assessent.
Emissions and their dispersion need not be monitored for extended periods,
unless the data collected prove to be inconclusive. Data acquisition in the
vicinity of emissions and in locations some distance from sources should be
conducted to determine before-and-after changes in air quality. Planning of
data analysis is recommended to determine what data are to be collected to
meet end-use requirements.
Short-term intensive monitoring is recommended to determine the
relationship of dispersion data to the fixed monitoring sites. Redundant
monitoring technology should be applied concurrently to make efficient use of
different forms of data. Airborne and ground-deployed sampling systems are
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effective in this approach and can include sampling methods to determine the
relationship of air quality measurements to source contributions.
Since the largest volume of data collected at NAS Miramar will be from
ground stations in the vicinity of emissions, it is essential that rigorous
statistical tests be applied to the data set to document air quality variation
between monitoring stations. Information obtained at this stage can then be
correlated with special study results to provide a complete assessment of the
data for impact determination, documentation of standards compliance, and
identification of emission source categories. Because of the San Diego locale
involved, a primary objective will be the determination of background air
quality prior to any airbase influence as a function of the predominant
meteorological conditions.
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REFERENCES
1. Platt, M., R. C. Baker, E. K. Bastreass, K. M. Chang and R. D. Siegel.
1971. The Potential Impact of Aircraft upon Air Quality. Northern
Research and Engineering Corp., Report No. 1167-1, NTIS No. PB208-950.
2. Rote, D. M., I. T. Wang, L. E. Wangen, R. W. Hecht, R. R. Cirillo and J.
Pratapas. 1973. Airport Vicinity Air Pollution Study. Argonne National
Laboratory Report to Federal Aviation Administration, Report No.
FAA-RD-73-113.
3. Thayer, S. D., D. J. Pelton, G. H. Stadskler and B. D. Weaver. 1974.
Model Verification - Aircraft Emissions Impact on Air Quality. Geomet
Report No. EF-262, EPA Contract No. 68-02-0665.
4. Rote, D. M. and L. E. Wangen. 1975. Generalized Air Quality Assessment
Model for Air Force Operations. Air Force Document No. AFWL-TR-74-304,
NTIS No. ADA-0006-807.
5. Segal, H. Monitoring Concorde Emissions. 1977. J. Air Pollut. Control
Assoc., 27(7):623630.
6. Naugle, D. F., B. C. Grems and P. S. Daley. 1977. Air Quality Impact of
Aircraft at Ten US Air Force Bases. APCA 77(41):6.
7. Jordan, B. C. 1977. An Assessment of the Potential Air Quality Impact
of General Aviation Aircraft Emissions. EPA Office of Air Quality
Planning and Standards.
8. Haber, J. M. 1975. A Survey of Computer Models for Predicting Air
Pollution from Airports. J. H. Wiggins CO., Report No. 75-1231-1.
9. Los Angeles County Air Pollution Control District. 1971. Study of Jet
Aircraft Emissions and Air Quality in the Vicinity of the Los Angeles
International Airport. NTIS No. PB198-699.
10. Naugle, D. F. and P. S. Daley. 1978. Air Quality Impact of Ten USAF
Bases. APCA 28(4).
11. Herget, W. F. 1977. Nonextractive Electro-optical Measurement of Jet
Engine Emissions. FAA-RD-78-10.
12. Terminal Forecast Reference Notebook. 1974. Base Weather Station,
Williams Air Force Base, Arizona. December 1974.
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13. Zeller, K. F. and R. B. Evans. 1976. Airport Air Pollution Monitoring
Program. APCA 76(11).
14. Rote, D. M., R. J. Yamartino and K. L. Brubaker. 1978. Preliminary
Evaluation of AQAM at Williams AFB. Conference on Air Quality and
Aviation, Reston, VA, October 1978.
15. Robinson, E. and R. C. Robbins. 1978. Sources, Abundance, and Fate of
Gaseous Pollutants. Stanford Research Institute (for the American
Petroleum Institute), NTIS N71-25147.
16. McElroy, F. F. and V. L. Thompson. 1975. Hydrocarbon Measurement
Discrepancies Among Various Analyzers Using Flame lonization Detectors.
EPA-600/4-75-010.
17. Bromberg, S. M., B. I. Bennett and R. L. Lampe. 1978. Summary of Audit
Performance Measurement of S02, N02, CO, Sulfate and Nitrate-1976.
EPA-600/14-78-004.
18. Graf, F. J. and R. G. Draftz. 1976. Microscopial Identification of
Aerosols Collected at Williams Air Force Base. IITRI, EPA Grant No.
R803078-02-0, August 1976.
19. Tombach, I. 1971. Measurement of Some Optical Properties of Air
Pollution with the Integrating Nephelometer. In: Proceedings of the
International Conference on Sensing of Environmental Pollutants, AIAA
Paper No. 71-1101, Palo Alto, California, November 1971.
20. Breeding, R. , et al. 1973. Background Trace Gas Concentrations in the
Central United States. J. Geophys. Res. 78:7057-7064.
21. Breeding, R. , et al. 1976. Measurement of Atmospheric Pollutants in the
St. Louis Area. Atmos. Environ. 10:181-194.
22. Jones, D. C. and M. Lahue. 1976. Background Ozone Concentration in
Western Colorado. Ozone/Oxidants Interaction with the Total Environment
Conference, Dallas, Texas, March 1976.
23. Turner, D. B. 1969. Workbook of Atmospheric Dispersion Estimates. U.S.
Dept. of Health, Education, and Welfare Public Health Service, AP-26,
Cincinnati, Ohio, 1969. pp. 37-40.
24. Environmental Measurements, Inc. 1976. Moving Laboratory Survey at
Williams Air Force Base. EPA Contract No. CB-6-99-3160-A, San
Francisco, California, December 1976.
25. Raytheon Company. 1976. Airport Pollution Mapping, Final Report.
Raytheon Report ER76-4140, Sudbury, Massachusetts.
26. Friedlander, S. K. 1973. Small Particles in Mr Rose a Big Problem.
Environ. Sci. & Tech. 7(13):1115-1118.
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27. Natusch, D. F. and J. R. Wallace. 1974. Urban Aerosol Toxicity: The
Influence of Particle Size. Science 186(4165):695-699.
28. Charlson, R. J. 1969. Atmospheric Visibility Related to Aerosol Mass
Concentration. Environ. Sci. & Tech. 3:10, 913-918.
29. Herget, W. F. 1976. Long-path Measurements of CO Concentrations at
Williams Air Force Base. EPA-Environmental Research Support Laboratory,
Northrop Services, Inc., Research Triangle Park, North Carolina.
30. Morris, A. L. and F. Hall. 1974. Remote Sensing of the Atmosphere by
Sound. National Center for Atmospheric Research Atmos. Technol. 6.
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TECHNICAL REPORT DATA
(flease read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/4-80-037
4. T
ITLE AND SUBTITLE
WILLIAMS AIR FORCE BASE
2.
USAF: ESL-TR-79-33
AIR QUALITY MONITORING STUDY
7. AUTHOR(S)
D. C. Sheesley, S. J. Gordon and M. L. Ehlert
9, P
12.
15.
16.
17.
a.
13.
ERFORMING ORGANIZATION NAME AND ADDRESS
Northrop Services, Inc.,
Environmental Sciences Center
Las Vegas, NV 89119
SPONSORING AGENCY NAME AND ADC
U.S. Environmental Prote
Office of Research and D
Environmental Monitoring
Las Vegas, NV 89114
SUPPLEMENTARY NOTES
1RESS
ction Agency Las Vegas
evelopment
Systems Laboratory
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
July 1980
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-03-2591
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/07
ABSTRACT
Air quality and meteorological data were collected continuously from a network
of five ground monitoring stations located at Williams Air Force Base WAFB)
near Phoenix, Arizona, during June 1976 through June 1977. Data reported here
will serve as detailed input for defining the accuracy limits of the Air
Quality Assessment Model. The data have been analyzed in order to determine
the air quality impact attributable to WAFB operations.
Also reported are the preliminary results obtained from several related
special studies designed to characterize horizonatl and vertical dispersion
of WAFB emisions. The data indicate no significant air quality impact at
WAFB resulting from aircraft operations.
DESCRIPTORS
air quality
meteorological data
DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
KEY WORDS AND DOCUMENT ANALYSIS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Williams Air Force Base 43 F
Air Quality Assessment 55C
Model 68A
19. SECURITY CLASS (This Report) 21. NO. OI- PAGES
UNCLASSIFIED 88
20 SECURITY CLASS (This page) 22. PRICE
' UNCLASSIFIED
EPA Form 2220-1 (9-73)
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