GUIDELINE SERIES
OAQPS NO. 1.2-012
GUIDANCE FOR AIR QUALITY MONITORING
NETWORK DBSIGH AMD INSTRUMENT SITING
US. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina
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GUIDANCE FOR
AIR QUALITY MONITORING NETWORK
DESIGN AND INSTRUMENT SITING
January 1974
OAQPS Number 1.2-012
Monitoring and Data Analysis Division
Office of Air Quality Planning and Standards
and
i
Quality Assurance and Environmental Monitoring Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina
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PREFACE
The Monitoring and Data Analysis Division of the Office
of Air Quality Planning and Standards and the Quality Assur-
ance and Environmental Monitoring Laboratory of the National
Environmental Research Center, Research Triangle Park, have
prepared this report entitled "Guidance for Air Quality
Monitoring Network Design and Instrument siting," for use
by the Regional Offices of the Environmental Protection
Agency and by State and local air pollution control agencies.
This report consolidates and updates information contained
in the previously issued air quality monitoring documents
listed below:
1. Guidelines: Air Quality Surveillance Networks, AP-98,
May 1971.
2. Guidelines for Technical Services o,f a State Air
Pollution Control Agency - Appendix A, U.S. Environ-
mental Protection Agency, APTD-1347, November 1972.
3. OAQPS Guideline Series 1.2-007, Air Quality Monitor-
ing Interim Guidance, August 1973.
Adherence to the guidance presented in this report will,
hopefully, lead to acquisition of more useable and mutually
compatible data by all States and Regions and will also facili-
tate evaluation of State air monitoring programs by the EPA
Regional Offices. Further, risks involved in policy decisions
concerning National Ambient Air Quality Standards should be
minimized.
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TABLE OF CONTENTS
1. INTRODUCTION 1
2. OBJECTIVES OP REGIONAL MONITORING 4
3. DESIGN OF AN AIR QUALITY MONITORING NETWORK 6
3.1 Factors Influencing Network Design 6
3.1.1 Source Receptor Relationships 7
3.1.2 Meteorology 8
3.1.3 Climatology 9
3.1.4 Local Effects 10
3.2 Size of Monitoring Networks . 12
3.2.1 Minimum Network (Existing Requirements) 13
3.2.2 Additional Monitoring (Suggested Guidance) 16
3.3 Location of Monitoring Stations 16
3.4 Sampling Frequency 20
3.4.1 Recommended Frequencies - Urban Areas 21
3.4.2 Recommendations for Isolated Point Sources 22
3.5 Isolated Point Source Monitoring 23
4. INSTRUMENT SITING 25
4.1 General Considerations 25
/'
4.2 Specific Considerations .' 27
/
5. REFERENCES 33
APPENDIX
A. Atmospheric Areas of the United States A-l
B. Possible Procedures for Determining the Scope of B-l
Additional Monitoring
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APPENDIX, Continued
C. Screening Procedure for Determining the Necessity C-l
of Monitoring Isolated Point Sources
D. Computerized Atmospheric Diffusion Models Avail- D-l
able from EPA
LIST OF FIGURES
1. Mean Daily Solar Radiation (Langleys) Annual. 11
2. Estimated Distance from an Elevated Point Source to the ~26™
Maximum Ground-Level Concentration.
3. Schematic of Cross-Street Circulation in Street Canyon. 29
LIST OF TABLES
1. Minimum Number of Air Quality Monitoring Sites 15
2. Distribution of Mechanical (Integrated) Sampling Stations 19
3. Distribution of Automatic (Continuous) Sampling Stations 19
4. Siting Guidelines for Areas of Estimated Maximum Pollutant 31
Concentrations
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1. INTRODUCTION
The primary purpose of this guideline is to provide the
Regional Offices of the Environmental Protection Agency (EPA)
and State and local air pollution agencies with updated gui-
dance on the principles and procedures involved in the design
of air quality monitoring networks with emphasis on the require-
ments of the State Implementation Plan (SIP) process. The
August 14, 1971 Federal Register (40 CFR 51) provided regula-
tions regarding the minimum size of networks to be operated
by the States to monitor progress in achieving the National
Ambient Air Quality Standards (NAAQS). These regulations
specify minimum networks that vary in size according to regional
priority classification and population. Full network implemen-
tation is required by mid-1974.
123
General guidelines ' ' have been issued which were
intended to provide a basic rationale for the development
and evaluation of air monitoring networks. These earlier
guidelines were largely subjective but did provide the best
knowledge in existence at the time. Much of the guidance pro-
vided by these earlier publications is repeated. Areas where
updated or new guidance is presented include: location of
samplers, instrument siting criteria, possible methods for
determining an adequate network size, and isolated point
source monitoring.
The guidelines presented here can be used to assist
State and local agencies in setting up air quality monitoring
networks. The development of an air quality monitoring net-
work includes determining the number and location of sampling
sites, selecting appropriate instrumentation, determining
frequency of sampling, and establishing instrument siting
criteria. Experience and technical judgment are essential
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for determining the number and location of sampling sites
because mathematical models or other methods may not be
entirely reliable.or, in some instances, may not be available.
The development and implementation of a network must by
necessity involve a trade-off between what is considered
desirable from a strictly technical point of view and what
is feasible with the available resources. An ideal network
will, in almost all instances, require more resources than
are available. In light of this, the design discussed in
this guideline centers on the minimally required monitoring
network—a network less than ideal, yet capable of meeting
the major monitoring requirements. The basic difference
between the minimally required monitoring network and the
ideal is that the minimal network has fewer and perhaps less
sophisticated instruments. Designers of the network should
attempt to maximize the effectiveness of the minimally required
network through careful selection of sampling sites, scheduling
of variable sampling frequencies, and possible use of mechan-
ical (integrated) as well as automatic (continuous) samplers.
This guideline does not cover specialized monitoring that
may be required concerning new issues such as indirect sources,
no significant deterioration, and supplementary control systems.
Information on air monitoring involving these issues and other
new issues will be provided separately either in the regula-
tions or in guidance issued at a later date. Furthermore,
specific detailed guidance is being developed on an individual
pollutant basis covering the design and operation of the moni-
toring station network. It should be recognized that air
monitoring networks are dynamic and, thus, should be flexible
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enough to allow for changing air pollution patterns as well
as the resolution of new issues. Hence, network design is
not a one-time event. An evaluation of a monitoring network
and how it meets the objectives of an air program should be
performed periodically. Stations could be moved whenever the
needs of an agency change sufficiently enough to warrant the
move. Some stations, however, should be designated as trend
sites and not be moved. This will allow for analysis of long-
term air quality trends.
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2. OBJECTIVES OF REGIONAL MONITORING
Regional air quality monitoring networks are required as
part of the implementation plans currently in effect for sulfur
oxides, particulates, carbon monoxide, oxidants, and nitrogen
oxides. Generally, monitoring networks for all of these pollu-
tants must be established in a region. Although each pollutant
requires separate analysis, the collection of samples can be
generalized into two groups: (1) a particulate network, which
is the source of information for suspended particulates, and
(2) a gas network, which consists of sampling devices for CO,
S02, NO2» non-methane hydrocarbons, and oxidants. The need
for monitoring for each pollutant will depend on the amount of
pollution present within the region. For example, whereas one
region may require extensive monitoring of, say, oxidants, the
relative absence of this pollutant in another region may pre-
clude such an extensive monitoring effort.
Air quality monitoring within a region must provide infor-
mation to be used as a basis for the following actions:
1. Judging compliance with and/or progress made toward
meeting National Ambient Air Quality Standards.
2. Activating emergency control procedures intended to
prevent air pollution episodes.
3. Determining pollution patterns and trends throughout
a region including its nonurban areas.
4. Developing a data base for the assessment of health
and welfare effects, for land use and transportation planning,
for the study of pollutant interactions, for the evaluation
of abatement strategies and enforcement of control regulations,
and for validation of mathematical models.
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It should be recognized that the overall goal of an air
quality monitoring network is the protection of human health
and welfare. This report, however, stresses compliance with
SIP requirements because it is the regulatory process set up
to protect human health and welfare through the achievement
of NAAQS. While the two goals are generally compatible, there
are instances where the health and welfare aspect should pre-
vail. For instance, where uncertainty exists between two
possible sampling locations, the one surrounded by a greater
density of population should be given preference
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3. DESIGN OF AN AIR QUALITY MONITORING NETWORK
In the design of an air quality monitoring network, know-
ledge of the factors influencing air quality and information
needed for determining the number, location, and siting of
monitors is essential. This section presents a discussion
of these factors and of possible methodologies that may be
used in the design of the network.
3.1 Factors Influencing Network Design
The design of a sampling network will depend mainly on
the magnitude and distribution of pollutant concentrations
within a defined area or region. Pollutant concentrations
vary both in space and in time. Variations occur as a result
of the interplay among various factors including source
strengths, emission characteristics, meteorology, climatology,
topography, and urban effects as well as by chemical trans-
formations and natural removal processes. Selection of the
number and location of sites for a network should properly
account for these factors. Most of these factors are incor-
porated into dispersion models (see Appendix D) which along
with past air quality measurements are used to estimate the
probable air quality isopleths throughout a region. Isopleth
maps of ambient concentrations so derived are the best tools
for determining the number of stations needed and for suggest-
ing station locations. In the absence of adequate or appropri-
ate models and/or past air quality data, techniques involving
some of the factors may be used to aid in network design.
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The following discussion briefly describes the major
factors influencing air quality and how knowledge of these
factors may be used in designing an air quality network.
3.1.1 Source-Receptor Relationships
Source-receptor relationships are concerned with source
strengths and emission characteristics and how they affect
pollutant concentrations at receptor sites. This information
is utilized in dispersion modeling to indicate zones of con-
centration maxima, to locate monitoring sites, and to determine
the type and number of samplers. <
An emission inventory is a prime prerequisite for proper
design of a network. In the absence of such an inventory,
information on distribution of major sources, population,
transportation networks, and present and projected land uses
can be quite useful. This information along with available
data on meteorology, topography, and dispersion characteristics
will indicate the major features of pollutant distributions.
For reactive pollutants such as oxidants which form in
the atmosphere from photochemical processes, the primary
factors affecting ambient concentrations are:
. Concentration of reactive precursors
. Intensity of solar radiation
. Atmospheric stability
. Low-level transport winds.
Reactivities of photochemical pollutants can vary substan-
tially from place to place depending oh the mix of photochemically
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active constituents in the air. Solar radiation varies con-
siderably in different parts of the country as well as with
the season and time of day. On sunny days when photochemical
processes are more prevalent, the atmosphere tends toward
instability. Transport wind information along with some assump-
tion or measure of stability can be used in locating suspected
areas of concentration maxima. The usual source of such meteoro-
logical information is airport weather observations. Summaries
of daytime conditions are preferred for photochemical considera-
tions.
3.1.2 Meteorology
Major meteorological factors that influence pollutant
concentrations are:
* The vertical Structure of Horizontal Wind and its
Variability
Winds transport and dilute pollutants between sources
and receptors. Variations of wind direction markedly
influence concentrations at receptors. Light winds
generally tend to increase concentrations over wide
areas.
. Atmospheric Stability
Pollutant dispersion is inhibited in stable air which
accompanies temperature inversions and is enhanced by
the instability caused by thermal and mechanical tur-
bulence.
. Mixing Heights
This parameter is defined as the height above the
surface through which vigorous mixing occurs. Mixing
height normally reaches a minimum in the early morning
and a maximum in the afternoon. Low afternoon mixing
heights are often indicative of poor dispersion con-
ditions.
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. Solar Radiation
Both the intensity and duration of solar radiation
are important to the formation and buildup of photo-
chemical pollutants.
3.1.3 Climatology
Dilution Climatology
Dilution climatology is defined as the combination of
meteorological conditions which affect the interchange and
dispersion of pollutants of relatively large areas. Such
factors are the frequency, persistence, and height variation
of wind speed and direction of stable (inversion) layers of
air and of mixing heights. Collectively, an assessment of
these factors provides a measure of the dilution climatology
of an area. Dilution climatology accounts for the effects
of large scale topographic features such as large bodies of
water and mountain ranges. The relative recurrence of short-
term phenomena such as stagnation episodes is considered.
Small scale obstructions such as hills and buildings are
classified as localized influences and are not considered in
dilution climatology.
Atmospheric areas possessing similar dilution climatolo-
gies have been defined on a geographic basis and include all
Air Quality Control Regions in the contiguous United States
(Appendix A). Attached to Appendix A are interim definitions
for areas outside the contiguous U.S. for which AQCR's have
been designated. Atmospheric areas are used in Appendix B
to derive relative numerical indicators of the possible need
for additional monitors in an adequate network.
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M;"\cm _ Solrn: Radiation
The dilution climate of an area while important to the
accumulation of secondary pollutants once they form does not
influence thqir formation. Figure 1 shows relative solar
radiation, throughout the contiguous U.S. and can Toe used as
an additional tool to indicate the needs for monitoring secon-
dary pollutants.
3.1.4 Local Effects
Topography
The dispersion patterns in some sectors of an area or
region can be significantly altered by local topographical
fcictors. Those which will be used in this guideline along
with meteorological factors to indicate need for additional
monitors in an adequate network, are:
. Valley Effects
Valleys tend to channel the wind flow along their
axis, restrict horizontal dispersion, increase the
tendency for inversions to form, and may cause aero-
dynamic downwash from stacks, not extending above the
valley walls. Air quality discontimiities between
valley-ridge sectors often exist. Thus, valleys
almost alwciys need monitors in excess of the
required minimum's.
. Shoreline Effects
Airflow along shorelines undergoes frequent changes
brought about by the changes in relative temperature
of the e'.ir and water. Discontinuities a-nd conver-
gence x.onos in the clisparsicn patterns occur which
indicate need for monitoring beyond required minimums.
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Figure 1. Mean dally solar reflation (langleys) annual. (Stern, 1968)
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. Hilly and Mountainous Terrain Effects
Complexities introduced by hills and mountains include
disrupted airflow patterns, intersection of their
interface by elevated plumes, induced mechanical tur-
bulence and more frequent inversions in low-lying
protected areas. Hilly and mountainous terrain usually
increase the need for monitors.
Urban Effects
Virtually all meteorological parameters are influenced
to some extent by cities. Urban effects tend to modify
meteorological parameters in the following major ways rela-
tive to rural locations:
. Wind direction variability is increased
. Average wind speeds are lighter
. Instability is increased
. Mixing depths are greater
. Local influences are greater.
The complexity and variability of urban factors do not
allow general quantitative assessments. Therefore/ in this
guideline, urban effects are not used directly to indicate
the number of sites that may be needed. Instead, the user
should be aware of urban effects when considering other factors
(such as meteorology, climatology, etc.) and should make adjust-
ments where necessary which allow for urban influences.
3.2 Size of Monitoring Network
The basic network size refers to the number of monitors
needed or required to fulfill the objectives of a monitoring
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program. Ultimately, the number of sampling stations neces-
sary will depend primarily on the existing pollution levels,
their variability, and the size of the region (availability
of resources is also an important consideration). The size
of the network, however, must be sufficient to define the
area(s) where ambient concentrations may be expected to exceed
air quality standards. Information on air quality in other
areas including the nonurban portions of the region should be
also collected.
In many AQCR's, there is a need to increase the level
and intensity of monitoring for carbon monoxide and oxidants.
On the other hand, S02 and TSP existing networks appear to be
adequate in most of the AQCR's for fulfilling the objectives
of the SIP's.
The following subsections review existing guidance on
the design of minimally adequate networks-Representing the
lowest level of monitoring activity commensurate with overall
air quality objectives. Possible procedures for supplementing
the minimum network to. more adequately fulfill monitoring
objectives are presented also.
3.2.1 Minimum Network (Existing Requirements)
A first approximation to the minimum number of stations
required in a region may be obtained from general curves based
on a qualitative evaluation of cities of different population
*
classes in terms of their existing networks pollution patterns,
geographic distribution of sources, and the like. The relation-
ship between population and network size (see below) was derived
4
from such investigations, combined with experience. In general,
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population is a good index to determine network size. In
certain situations, however, such as the relative absence of
sulfur dioxide in some western portions of the U.S., such
relationships may not be applicable. In these situations,
additional information such as source strengths and their
locations is essential before a network size can be deter-
mined .
Based on the above population relationship and according
to a priority classification assigned to each AQCR for carbon
monoxide, nitrogen dioxide, particulate matter, photochemical
oxidants, and sulfur dioxide, the minimum size of an air
quality monitoring network was determined. An AQCR was
assigned a priority classification according to a comparison
of its air quality levels to the air quality standards or
based on its potential for violation of an air quality stan-
dard. Generally, in Priority I AQCR's, the air quality is
poorer than primary standards. In Priority II regions, it
is between secondary and primary levels and in Priority III
regions, it is better than secondary standards. For parti-
culate matter and sulfur dioxide, the classification criteria
provide for Priorities of I, II, or III while for carbon
monoxide, nitrogen dioxide, and photochemical oxidants, Priori-
ties of I or III are applicable.
Table 1 presents the minimum number of air quality moni-
toring sites by AQCR classification and population class.
Note that the reference method for nitrogen dioxide has been
revoked. Three candidate methods have been proposed to replace
the former reference method. An evaluation of these methods
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Table 1. Minimum Number of Air Quality Monitoring Sites
Pollutant
Bcgtsn papcUatloa
number of air
monitoring clta b
Btupendcdparticulattt... High volmaocsm^sr
. Loos than 100,000 ...4.
100.009-1.000,000... 0+0.6 mt 100.000 population.*
S,Ctt3,C91'*3,GtlO,CttO_......^. 7.04-O.sJpsr 109*000population."
Abovo 0,090,000 £2+0.18$^ USWED population.
Gsb RC?C2S,6!tO population o up
Bultardloxtdo Pdonaasflmoerc^BSvofcat'1. Oao34-H«iairssapJoovoryOdayo
Ocfboo mo&o&ido. ..... Wc3idl8p3nrfvotafrorcd o?
n..
Nitrogen dioxide 24-hour sampling method
ma&oS).
. Suspended partleulatca... Slab volomocampiar.
Ono 84-hour sample 0701714
CajTo foes bobbKT).b
Kilo.
, Suspended pertlcalnto-.. ffl(3t» vofcana easier
Sulfur dioxide .»PraontzssJllno er
Lcsn than 100.000 '.-.8.
109.000-1,000,000 SJ+0.6 per100.000 population.'
E,eJO.CM-0,CliO,eOO G44.1B no; 100,000 population.<•»
AbovoS.000.oao H-KMOplr 100,000 population.
Xon than 100.000. 1.
K3^J2!Mi,OBO,ero 1-t-O.IB par 100,000 population.'
A&OTO WBO^SS) (K-O.C3 par 100,000 population."
y^yv\ ^fonn Iffy I'liliy 1.
££D,6tt(WJ,GBO.COO........_.. 1+0*1B psr 100,000 population.0
At(»vo6,Otta.Ctt) O-fS.03 par 100,000 population."
Lcia than 140,000. 1.
!C3,CMH1,000,COO_.'_ 1+O.lB psr 100,020 population.0
Abovo 8,000,000 6+0.03 E»rlOC,TOB population.'
Lea) than 100,000 ,..3.
!-1,COO,OIHI . _
At»vo l.TOO.CttO. 10.
a.
,^)^^-^^ to nearest ^hole number.
ITEmciP&iScsistrte&otsatlon (nrovtdcd Tc£on is used throughout the Instrument uystem In parts exposed
), (O)'Couloinotrfc Detection (provided
a Equivalent to 61 random samplo iws- TOST.
o Kqulvolcnt to 88 random aompfca per yc27.
° Total population of a region. Whon resumed BU
d Equivalent methods en (1) Ota ChromatosroptUo t
to the air stream), (2) Flame Photometric Dotcstloa (proi
n and reducing interferences ouch GO On. NOn. cad HtS cro romO7«3), cs& M 06o oBtomntrf
° Bqulvalent method la Oes Chromato^rophlc Sopsrotton—CoteJytta CsavCToam—Ptomo lonloatlea Dctcstlan.
' Equivalent methods arc (1) Potcsalure ZodWo Cotartmotrlc DotosStoa (provtoScd o atrrssttoi b ftrfe to BO» cod NOi), (2) TJV Ffc^omotrts Doteotlon of Otsono
(proirldad nnrnpatmntlnn ta tn^o >nr jnt/>rf»rinj raiJ^TtniM.^!) TOMJ (51) nVTa^Mmlnr-v-agl rfcittMMfa ta8gia Ko GC2£aial c±iafcr&) to asrtjsa suacdda olferc^ca dioxide, oud
^otoehemloal oxldants; therefore, no moaltofas otto cro rcaulrea to KJCO '
. b IB intorotato rcjloua. tho Bomber cl tifca fcjutrcfl C
Bpeclflrotlon
PhotcchamlcJ ozldant
(cosraCcfl Co? NOi and 8Oi)
Range 0-2,60) rtj./ta.' (0-1 p.pjn.)
Minimum detectable sensitivity 28 0s./m.» (0.01 p.p.mj 0.9 mg
Rise time, 80 peroant 6 minute! 0
Fall time, 80 percent 8 minutes
ZerodrUt :.•=•! percent per day and *2panwnt per
8 days.
Spsndrift ==•! peroant per day and <=>2 psreoat pc? _
Sdayo. Bfiosa.
Precision - "=>2paraB»t ^OpxsaaD
Operation period ;.. OdojB - •- 0%y°-——.iLw —,-,-
Noise oO,apasront(fullcJnlo) e-ojpareant(te3c=2a)
Interfcrenoa equivalent J3 f^ym." (6^11 p.pja.)
Operating temperature fluctuation oC°C
Linearity 3psreant (fullsoslo)
o-aso neJa." (o-oj P.O.SL).
20 pa./m.0 (0.01 p.p
par day acO ^2 pamnt per
pcrtcnt par day and £>2 percent PCI
'
...•. Odoyrj.
Specification
Nltrosan dtelda
Bvdrocarbttns (ecrrected for metbaaa)
Ranga 0-1880(jg/m» (0-1 p-pjn.) 0-0 mg/m« (0-an.p.snJ.
Minimum detectable onsttlvlty.... 18nS/m» (0.01 p.pjn.) 0.1S ma/m" (0^3 p.8>J3j.
Rise time, 90%..... Onunuta Omtnntn,
Falltlma, 60% 0 minutes , Ommotca
Zero drift. ±1% per day and ±8% psr 8 days il% par day and ±2% per 0 doyo,
(full scale). (mUcoota).
Span drift ±1% par day and i2% par 3 days ±1% pa- day and ±2$S per 8 tora
(rail czato). (fuJl ccate).
Precisian &<% ptt-
Oporetlou iwrlod. : Bdays. 8 dA»% (fun stay.
Interference equivalent 1» pa/m" (0.01 p-iua.) O.CD mgAn0 (0.03 p.p.m.).
Operating tcmperaturo fluctuation. &u°C J^°C.
Lineortty ^5 (tuHODla) S>5 (ftdl C03to).
The various specifications are defined as folloon:
Range: The minimum and maximum measurement limits.
Minimum detectable sensitivity: The smallest amount of Input ooneontrotkm crhteh can bo £tte«le6 DO oonoantrotion opproaehos sen.
Rise time 80 percent: The Interval between Initial response time and ttmc to 80 parent roponce oKcr o step mcreasa hi Inlet eonesatrottsn.
Fall time 80 percent: The Interval between Initial response time and time to 80 paroent response otto o step decrease In the inlet eonscntrotioa.
Zero drift: The change in Instrument output owr a stated time period of unadjusted continuous'operation, when the input eonoantroUon Is cero.
Span drift: The cliange In Instrument output over a stated period of unadjusted continuous operation, when the Input concentration til a stated upscale value.
Precision: The degree of agreement between repeated measurement] of the sama concentration (which aboil ba the midpoint d tbo stated ranse) expressed £3 tbo
average deviation of the single results from the mean. • •
Operation period: The period of tlma over which the Instrument can be expieted to opsroto nnattondcd within BpssSfleatiKn. .
Noise: Spontaneous deviations from a mean output not caused by Input concontrotton ehongio.
Interference equivalent: Tho portion of Indicated concentration duo to tho totcref the Interferences commonly found In ambient oh".
^IlterlerCIlGC UlJUlVUIUJIb: A I1U pwl LIUII UJ II1U4V41M:U MJIM^l-lftlaMUJI uuu «v »!«« M#«^3 va *«.o Jllvw H^TTtl^vo ^v. ft
Operating temperature fluctuation: The ambient temperature flu'ctaotton
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is still underway. Meanwhile, in cases where it appears
desirable to continue NO2 monitoring activities, the Jacobs
Hochheiser technique should not be used.
3.2.2 Additional Monitoring (Suggested Guidance)
It is recognized that the scheme for determining the
minimum requirements of an AQCR written in regulation form
may not be flexible enough to allow for adequate monitoring
in every AQCR in the country. Further, issues and new require-
ments such as no significant deterioration, indirect sources,
transportation control plans, and supplementary control systems
may have increased the need for monitoring above the minimum
requirements. Appendix B presents two possible methodologies
which may be used for determining an adequate network size.
One is based on the existing pollution levels and patterns
in an area. The other is based on the application of topo-
graphic and climatological weighting factors to the minimum
implementation plan monitoring requirements.
Both methods apply only to SC^ and TSP and Priority I
oxidant and N02 AQCR's. CO is not covered because it is
usually more of a localized rather than a regionwide problem.
Priority III AQCR's do not require monitoring for CO, oxidants,
and N02 at this time.
3.3 Location of Monitoring Stations
Selecting the locations of stations and samplers involves
decisions regarding (1) distribution of samplers within the
region and (2) specific site selection for each station. The
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first decision requires consideration of monitoring objec-
tives, overall pollution patterns, and the needs for govern-^
mental jurisdictional coverage. Selection of the particular
site is based on representativeness of the area and other
practical aspects such as housing the samplers, electric
power, and security from vandalism.
The information required for selecting sampler location
Is essentially the same as that for determining network size,
i.e., isopleth maps, population density maps, source loca-
tions. Following are suggested guidelines: .
1. The priority area is the zone of highest pollutant
concentration within the region. One or more sta-
tions are to be located in this area.
2. Close attention should be given to densely populated
areas within the region, especially when they are in
the vicinity of heavy emissions.
3. For assessing the quality of air entering the region,
stations must also be situated on the periphery of
the region. Meteorological factors such as frequen-
cies of wind direction are of primary importance in
locating these stations.
4. For determining the effects of future development on
the environment, sampling should be undertaken in
areas of projected growth.
5. A major objective of monitoring is evaluation of the
progress made in attaining the desired air quality.
For this purpose, sampling stations should be stra-
tegically situated to facilitate evaluation of the
implemented control tactics.
6. Some information of air quality should be available
to represent all portions of the region.
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The air quality monitoring network should consist of
stations that are situated primarily to document the highest
pollution levels in the region, to measure population exposure,
to measure the pollution generated by specific classes of
sources, and to record the nonurban levels of pollution. Many
stations will be capable of meeting more than one of these
criteria; e.g., a station located in a densely populated area
besides measuring population exposure could also document the
changes in pollutant concentrations resulting from new control
strategy employed in the area.
Although the sampler locations depend on many factors,
some idea of sampler distribution may be obtained from Tables
2 and 3, which show sampler location as a function of network
size. Table 2 summarizes distribution of mechanical samplers,
such as Hi-Vols; Table 3 shows distribution of automatic
samplers. With respect to locations shown in Tables 2 and 3,
it will be necessary to consider wind patterns, source loca-
tions, and distribution of emissions in selecting approximate
locations for these sites. For example, stations in the highly
populated area should be so situated that they can accurately
assess the pollution impact under different meteorological
conditions. Although both types of stations follow the same
general pattern, the tendency is for wider distribution of
mechanical sampling stations.
In the case of the reactive secondary pollutants, the
best sampling locations are, in most cases, away from the
sources which emit the necessary precursors (and contribute
to the reaction processes). Thus, the use of emission density
-------
19
Table 2. DISTRIBUTION OF MECHANICAL (INTEGRATED)
SAMPLING STAUQNS3
Number of stations
Total number
of stations
1
2
3
4
5
10
15
20
25
30
Center city/
industrial
1
1
2
2
2
5
8
12
14
17
Residential
zones
-
1
1
2
2
3
5
6
8
10
in:
Nonurban
' '• . —
- •
.
• -
1
2
2
2
3
3
Includes Hi-^Vol sampler S02 and NO,, 24-hour collectors
(for oxidants, a sampling time over 20 minutes is not
recommended) .
least one monitor for each pollutant should be in the
area of maximum concentration.
Table 3. DISTRIBUTION OF AUTOMATIC (CONTINUOUS)
SAMPLING STATIONS3
Total number
of stations
1
2
3
4
5
6
10
15
Number
Center city/
industrial
1
1
2
2-3
3
4
6
10
of stations in:
Residential
zones Nonurban0
— ' _
1 .
1
1-2
2
2
4
5
Includes S02, CO, No2, and ^
At least one monitor for each pollutant should be in
^ the .area of maximum concentration.
'Where ozone damage has been identified in nonurban areas,
monitoring may be necessary.
-------
20
and land use maps are not always helpful in determining sam-
pling site locations. They can, however, be used in conjunc-
tion with information on the direction and magnitude of
prevailing mid-morning winds to provide approximate sampling
locations. In general, the maximum concentrations are indi-
cated to occur between 5 and 15 miles downwind from the
downtown or area of heavy traffic density. However, if the
winds are light and variable, high levels may occur in the
vicinity of the pollutant emissions such as the center city.
The location of good NO^ and oxidant sampling sites is a diffi-
cult process and in many cases is based largely on intuition
or trial and error. The use of mobile N(>2 and oxidant samplers
could be helpful in locating areas of high concentration.
It is the intent of these guidelines to suggest that a
simple network be developed to measure the concentration of as
many pollutants as possible. It is likely that common sites,
although not necessarily ideal for each pollutant, may be
selected to provide adequate coverage for the pollutants of
concern. Each pollutant, however, should be considered indi-
vidually during the design phase to pinpoint pockets of high
pollution that otherwise might be overlooked.
The final task in determining sampler placement is to
find a specific location with the proper facilities for oper-
ating the sampler. Availability of space and power, accessi-
bility, security, and representativeness of the site determine
the precise location.
3.4 Sampling Frequency
Sampling averaging times depend mainly on the primary use
of the data. Accordingly, to show compliance with, or progress
-------
21
towards meeting ambient air standards, the sampling system
must be capable of producing data consistent with the aver-
aging times specified by the standards.
Current regulations specify the frequency of sampling
for the criteria pollutants to meet minimum requirements
(Table 1). Continuous sampling is specified except for 24-
hour hi-volume for suspended particulate matter and 24-hour
gas bubblers for S02. (At this time, the frequency that may
be specified for N02 sampling is not known.) The hi-volume
and gas bubbler measurements are required in all AQCR's at
least once every six days, equivalent to about 61 random
samples per year. Twenty-four-hour samples should be taken
from midnight to midnight (LST) to represent calendar days
and to permit direct utilization of the sampling data with
standard daily meteorological summaries.
The following are recommended frequencies for non-con-
tinuous, hi-volume, and bubbler sampling in order to more
adequately define TSP and SO, levels relative to the NAAQS.
3.4.1 Recommended Frequencies - Urban Areas
In general, the importance of measurements made at the
most polluted sampling sites in an urban AQCR makes it advis-
able to increase the frequency of sampling at those sites
above the minimum requirements. It is recommended that the
most frequent hi-volume samples be taken at the site(s)
where the highest 24-hour and annual averages are expected
based on past measurements or modeling estimates. This pro-
cedure will minimize the uncertainties in determining whether
T''.*'i k" ^
-------
the 24-hour NAAQS levels for particulate matter were exceeded.
Correspondingly, a more precise estimate of the annual average
will also be derived.
For SO2, continuous instruments can be used in place of
bubblers in areas of maximum concentrations. Accordingly, it
is recommended that in Priority I AQCR's, the continuous sam-
pling sites cover the areas of highest 24-hour and annual
average concentrations. This constitutes no significant
change from present requirements for S02 monitoring.
For TSP and S02, resources are generally not available
to operate the entire network on a daily basis. Adequate
coverage may be maintained at non-critical sites (i.e., sites
other than maximum concentration sites) with intermittent sam-
pling at frequencies calculated statistically for desired levels
of precision. In order to increase the statistical precision
of the estimate for the annual average, a systematic sampling
schedule should be utilized, such as suggested by Akland.
Also, the frequency of air monitoring necessary to character-
ize an air pollutant for a given time period and area can be
determined from statistical relationships that predict the
precision of the sample mean as a function of the frequency
of sampling, the standard deviation of the logs of the indi-
vidual measurements, and the level of confidence. Thus, the
minimum frequency requirements may not be adequate for all
locations and levels of confidence desired.
3.4.2 Recommendations for Isolated Point Sources
For isolated point sources, the areas of maximum concen-
tration on a short-term (up to 24 hours) are of primary concern.
-------
23
Experience has shown that such sources rarely cause violations
of long-term (annual) standards. S02 and TSP sources shown by
the method in section 3.5 to have the potential for causing a
violation of NAAQS should be monitored by at least one downward
site more frequently than minimally required. Specifically, at
this site, continuous instruments for SOj and sampling more
frequently than once every six days for TSP is advised.
Bubbler (24-hour) sampler(s) at the key site(s) are less
desirable because of the need for monitoring for the 3-hour
secondary S02 ambient standard. The 3-hour standard is especially
relevant in many nonurban areas because of its relation to vege-
tation damage.
The key site (s) for monitoring for isolated point sources
should be located on the basis of expected highest concentra-
tions for a given pollutant. Ordinarily, only NAAQS for S02
and TSP would be expected to be threatened by emissions from
isolated point sources; therefore, no recommendations for moni-
toring other criteria pollutants are made at this time.
3.5 Isolated Point Source Monitoring
Additional monitoring for point sources in multiple source set-
tings is not recommended unless models or other information
show that certain sources predominantly contribute to ground-
level concentrations. A predominant source in this context
would be defined as one which would contribute 90 percent or
more of the non-background concentrations over an extensive
area. In particular, models would also generally specify the
location of the maximum concentration expected from these sources.
-------
24
For isolated sources situated in relatively level terrain,
a screening model procedure* presented in Appendix C can be
utilized for making a determination of which particulate and
sulfur dioxide sources should be monitored. This procedure
is not applicable where turbulence in the wake of the plant
(emission source) building or nearby structure is apt to cause
aerodynamic downwash of the plume. The procedure is also not
applicable where concentration measurements at elevated levels
above ground (such as on tops of buildings) are desired or
where there are significant terrain features above the ground-
level elevation of the plant. Suggestions for identifying the
above circumstances follow.
Where the supporting structure for a stack or where build-
ings or other such obstructions exist within a distance of 10
stack heights and where the height of any of these structures
is more than 2/5 the height of the stack, then aerodynamic
downwash of plumes is likely to occur and a detailed analysis
of the specific case is necessary.
Similarly, a detailed analysis is needed where terrain
elevations more than 2/5 the height of the stack exist within
10 kilometers of a point source. In the latter circumstance,
the greatest impact may occur on the higher terrain under
meteorological conditions which are much different from those
assumed to cause the maximum in this procedure. Other unfore-
seen conditions may arise in evaluating the impact of point
sources which may necessitate detailed analysis.
*Note that this procedure does not apply to sources covered by
regulations for which monitoring is prescribed such as those
that may operate supplementary control systems.
-------
25
For each of the sources for which the need for monitoring
is determined from the above screening procedure, a minimum of
three sampling sites are suggested. Two should be along the
most frequent downwind direction(s) and one should be along
the direction that is predominantly upwind. Annual wind roses
can be used in this determination. The samplers should be
placed at distances where maximum short-term (1-24 hour) con-
centrations are most likely to occur. (The long-term annual
standards are unlikely to be threatened by an isolated point
source.) The distance to the maximum concentration is a func-
tion of effective source height and atmospheric stability. A
reasonable estimate of this distance can be derived from Figure 2,
Effective source height is the sum of physical stack height and
7
estimated plume rise. The Briggs plume rise or other appropri-
ate plume rise equations may be used. Where resources allow,
a preliminary sampling survey (possibly including mobile sam-
pling) should be.carried out to locate areas of maximum concen-
tration and to verify the appropriateness of dispersion estimates
4. INSTRUMENT SITING
4.1 General Considerations
In the selection of a particular site for a single sampler
or a complex station, it is essential that the sampler(s) be
situated to yield data representative of the location and not
be unduly influenced by the immediate surroundings. Little
definitive information is available concerning how air quality
measurements are affected by the nearness of buildings, height
-------
10 =
x
4
I I .0*
o
«• <
O K
18
- 3
X O
o
-------
from ground and the like. There are, however, general guide-
lines that can be provided based on operational experience:
1. Avoid sites where there are restrictions to air flow
in the vicinity of the air inlet—such as adjacent to
buildings, parapets, trees, etc.
2. Avoid sampling sites that are unduly influenced by
down-wash from a minor local source or by reentrain-
ment of ground dust, such as a stack located on the
roof of a building where the air inlet is located 6r
close to ground level near an unpaved road. In the
latter case, either elevate the sampler intake above
the level of maximum ground turbulence effect or
place the sampler intake away from the source of
ground dust.
3. The monitoring site should be generally inaccessible
to the public and should have adequate security^
electricity, and plumbing.
4. Uniformity in height above ground level is desirable.
Roof-top samplers should be utilized in moderate to
high density areas (in terms of structures). Ground-
level samplers should be utilized in low or sparse
density areas (in terms of structures).
5. For CO or N02 monitoring, samplers should not be
located in the median area of multilahe highways.
4.2 Specific Considerations
Specific guidelines for siting air monitoring stations in
areas of maximum pollutant concentrations are presented in
Table 4. These guidelines cover the monitoring of multiple
source areas; guidance for monitoring specific sources is
presented in Section 3.5.
Sulfur dioxide can be considered to be rather well mixed
near the ground at receptors not overly affected by specific
-------
point sources. Therefore, either ground or roof-top sampling
is recommended.
Similarly, TSP is usually well mixed within the first few
hundred feet above the ground, but only roof-top sampling is
recommended to avoid the influence of possible reentrainment
of particulates close to ground level.
Distance from the street is specified in the sampling
location guidelines for measuring peak 1-hour and 8-hour con-
centration values of CO because of the strong dependence of
CO concentration on nearness to the street. For the same rea-
son, height from the ground of the air inlet is more restric-
tive than for the other pollutants. It is desirable, however,
to sample as close as possible to the breathing zone within
practical considerations (i.e., proper exposure, security from
vandalism, minimizing surface effects, etc.). For peak CO
sampling within street canyons, the side of the street which
is opposite the side facing the roof-top-level winds is more
likely to experience the highest concentrations.(Figure 3).
The urban background site for CO should be utilized to
measure the maximum areawide concentrations to which the
general population is exposed. Thus, either roof top or
ground-level sampling in urban or suburban areas is recommended.
This station should not be adjacent to major thoroughfares (not
closer than 50 feet from the street curb) to rule out the influ-
ence of localized peaks due to roadway traffic.
There are no well established meteorological dispersion
models presently available for selecting areas of expected
maximum concentration for the secondary pollutants (oxidants
and N0~)• Probable high concentration areas described in the
-------
MEAN
WIND
BACKGROUND
CO CONCENTRATION
Figure 3. Schematic of Cross-Street Circulation
in Street Canyon (from users Manual
APRAC-1A, Urban Diffusion Model, Sep-
tember 1972)
-------
301
table for these pollutants are based on: (1) available infor-
mation on the reaction kinetics of atmospheric photochemical
reactions involving hydrocarbons, nitrogen oxides, and oxi-
dantsr (2) on diurnal variation in pollutant concentrations;
(3) on distribution of primary mobile sources of pollution/-
and, (4) on meteorological factors. A minimum distance away
from major traffic arteries and parking areas is specified
for the oxidant monitoring site because NO emissions from
motor vehicles consume atmospheric ozone. NG>2 is considered
both as a primary stationary source pollutant and as a secon-
dary pollutant and air monitoring stations for this pollutant
should be located consistent with the respective station
location guidelines. Differences in horizontal and vertical
clearance distances are based on increased probability of
reaction between reactive gases and vertical surfaces.
-------
able 4. SITING GUIDELINES FOR AREAS OF ESTIMATED MAXIMUM PDLLUTANT CONCENTRATIONS
POSITION OF
OLLUTANT CATEGORY
'rimary Stationary
source Pollutant
'rimary Mobile
source Pollutant
POLLUTANT
SO,
Particulates
CO (Peak)
CO (Urban
Background)
STATION LOCATION
Determined from atmosphere
diffusion model, historical
data, emission density, and
representative of population
exposure.
Same as above
Same as above
Representing area of high
traffic density, slow
moving traffic & obstruc-
tions to air flow (till
buildings) & pedestrian
population such as major
downtown traffic inter-
sections. 10-15 feet
from street curb.
Representing area of high
traffic density, but not
adjacent to aajor thorough-
fares, in center-city or ..
.suburban^ areas.. (>50 feet
from street curb). '
SUPPORTING VERTICAL CLEARANCE
STRUCTURE 'ABOVE SUPPORTING
STRUCTURE, FEET
Ground or
Roof Top
Ground or
Roof Top
Roof Top
Ground
Ground or
Roof Top
10-15.
10-15
10-15
10-15
5-10
5J.O
10-15
HORIZONTAL CLEARANCE
BEYOND SUPPORTING
STRUCTURE, FEETa _
* 5
>5
> 5
* S
-------
4. SITING GUIDELINES FOR AREAS OF ESTIMATED MAXIMUM IOLLUTANT CONCENTRATIONS (CONTINUED)
::.:;JTAXT CATEGORY POLLUTANT
Secondary Pollutant Oxidants
NO.
STATION LOCATION
Representing residei.tial
area downwind of dovntown
area (5-15 miles frcm down-
town and > 300 feet from
major traffic arteries or
parking areas).
Same as above
POSITION.OF AIR INLET
SUPPORTING VERTICAL CLEARANCE HORIZONTAL CLEARANCE
STRUCTURE ABOVE SUPPORTING BEYOND SUPPORTING
STRUCTURE. FE£Ta
Ground or
Roof Top
STRUCTURE. FEET
10-15
10-15
Ground or
Roof Top
? 5
> 5
10-15
10-15
>5
N*
Not applicable where air inlet is located above supporting structure,
Downwind of prevailing daytime wind direction during oxidant season.
When standard reference method (or equivalent) is suggested.
-------
33
5. REFERENCES
Guidelines: Air Quality Surveillance Networks, AP-98, U.S.
Environmental Protection Agency, Research Triangle Park,
North Carolina, May 1971.
Guidelines for Technical Services of a State Air Pollution
Control Agency, APTD-1347, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, November
1972.
OAQPS Guideline Series, Number 1.2-007, Air Quality Moni-
toring Interim Guidance, Monitoring and Data Analysis
Division, August 1973.
A Contribution to the Problem of Placement of Air Pollution
Samplers, NBS 10284, National Bureau of Standards, U.S.
Department of Commerce, Washington, D.C., May 1970.
Akland, J., Design of Sampling Schedules, JAPCA 22(4),
April 1972.
Hunt, W.F., The Precision Associated with the Sampling Fre-
quency of Log Normally Distributed Air Pollutant Measure-
ments, JAPCA 22(9), September 1972.
Briggs,G.A., Plume Rise, Atomic Energy Commission, Oak
Ridge, Tennessee, 1969.
-------
A-l
APPENDIX A
ATMOSPHERIC
OP THE 'UNITED STATES
DEPARTMENT OF HEALTH, EDU-
CATION, AND WELFARE
Office of the Seeretoty
AIR POLLUTION PREVENTION AND
CONTROL
Definition of Atmospheric Area*
Notice Is hereby given that, pursuant to
eccuan 107(a) of the Clean Air Act. M
•mended by the Air Quality Act at 1W7
(Public Law 90-146). the Atmospheric
areas of the Nation are defined M art out
below on the bads of those! conditions
which affect the interchange and dlffu-
alon of pollutants in the atmosphere.
Important meteorological parameters
that aflect the inUrchante and difluHon
or airborne pollutant! are the frequency.
persistence, and height variation of
stable (inversion) layers of air and speed
and direction of wind. Accordingly, the
boundaries of the Atmospheric areas are
based on annual averages of lew-
level inversion frequency. O» minimum
depths of vertical mixing, and (e) the
frequency of light winds.
Collectively, an assessment of these
parameters provides a measure of the
dilution climatology of an area, that is.
a history of the experience of air move-
ments as it relates to the dilution of pol-
lutants. This concept of dilution clima-
tology is em bodied in the High Air Pollu-
tion Potential Advisory System.
initiated by the National Center for Air
Pollution Centre] In the cart-
era milled Btataa In IM* and the western
United Slate in IMS, and no* adminia.
tered by the Environmental MeMe
Services AdmlaistJVtion (E8SA>. The
HAPP Advisory 3ntexa provide* a foiw-
can of weather conditions conducive to
the accumulation of air poOtstants over
large areas, a factor which was con-
sidered in the deflnHJon A the* AtakM.
pberic area*. •
Because of (he direct relationship of
the area boondarlw to the average ms-
teorological condition* of large-aeale
areas, these boradarke do aoi necessarily
reflect the actual meteorology in the
immediate vicinity of the boundaries. Ja
other word*, there wtt always be special
"boundary conditions" charaeterlatd by
the movement at air, together with air-
borne pollutants, aeroal the .boundary.
The boundaries are shown as aones on
the map in order to reflect this boundary
condition.
Furthermore, since the boundary be-
tween any two areas is defined by average
annual conditions, it fa) transitory on the
basis of shorter period. t«iil
conditions, with the result the* Wtts-
burgh. for exam pie, is under the Influenoe
of the average dilution cUmatoJogy of the
Appalachian Atmospheric ana during
certain umes of the year and under the
influence of the Ormt Ukes-Northeatt
Atmospheric area at other times (turns
the year. Sunllarly. Portland, ore*. New
York City, or any other place in the bear
' " ' ' '
rtelnlty of an Atmospheric area bound-
ary. «MM te under the Influence of a
Miffhborins AtmMpheile area during
certain periods.
Major topographical feature* are ako
reflected la Uw deUneatioa of Atmos-
pheric area*. The eastern boundary of
UW two AUmfapheric areas on the West
CoMUiM tor the magt pan at the 1.000-
to >,QOO-faot devatloB contour interval
on the western alopa of the first major
mountain chain, and it marks in gen-
eral the inland extent of the major
influence of maritime air, Tbe boundary
between the Rocky Mountain Area and
the Oreat Plata* Area is essentially
Mbktad at the 3*00- to «.000-fbot eleva-
!ttoa eontour interval TJfe eflecta of the
tains are apparent to the kraatkxn of
boundaries between Atmospheric areas
toi the eastern United States.
A brief itnn iljKli ii of each Atmo*-
* Pherie area is given in the attached table.
including the geographical extent of each
area aad the inajrc characteristic* of the
dilation climate. Definition of Atmos-
pheric area* ontaMe of the contiguous
United States has bean deferred.
; The existence of Atmospheric areas,
a* defined herein, don net to any way
Until the designation of Air Quality Con-
trol regions pursuant to section 107
of the Clean Air Act. M amended
;,, Dated: January S, 1863.
': tsxii) JOH» W. OABuno.
:;". ,-,'v-: '-. ' '• Secretary.
ATKOSPHOTC AfittS OF m UTtfTH) STATES
.. ::-:^..:tJ .^-.v., ,j..rfi .j'jf** •. •-. •• • •'- .AjB^rti^^tffctja/^i'.t**^-1.?'*: •».* •.'
ALIFORN1A
OREGON
COASTAL
AREA
~">rr>
-------
A-2
Atmospheric Area.s of the United States
NOTICIS
1 AiMBM^ie AMM *m_T"!M> c"***CT>ttt"e«« Aw Q«tun Act •» tMT,
-------
A-3
ATTACHMENT.
ADDITIONAL ATMOSPHERIC AREAS
Atmospheric Area
South Coastal Alaska
Extent of Aftea
From southern tip
along coast up to
30 miles Inland
to mouth of Yukon
River
North and Central
Alaska
The part of Alaska
excluding the
south coastal
section.
Tropical
Hawaiian Islands
Guam
Puerto Rico
American Samoa
Entire Areas.
Meteorological and
Topographical
Characteristics
Marl time air preva i1s
with light to moderate
winds along with
greater frequency of
fog, cloudiness and
precipitation and less
low level stability
than Inland and nor-
thern sections.
Characterized by
lenjtiiyj periods of very
strong "and persistent
Inversions in the cold
season. Long Alaskan
nights, almost eliminate
,the diurnal cycle of in-
verstoh - lapse conditions
typical of lower latitudes
Attendant Inversion
winds are quite low.
Storms are less frequent
than In South Coastal
Alaska.
The climate is predom-
inately tropical marine;
atmospheric stagnations
are prattlcally nonex-
istent; small incidences
of low level stability
except in topographically
protected inland areas.
Relatively good vertical
mixing prevails.
-------
B-l
APPENDIX B
The following are several possible methods for determining
a more adequate number of stations for an AQCR as contrasted to
the minimum required based on varying levels of Information.
Note that the actual number of stations finally decided upon for
a Region should be the result of tempering the derived number by
practical considerations, resources available, fuel use patterns,
and source configurations. Also the total adequate number of
monitors is found by summing the number necessary for the urban
area together with those needed for isolated point sources dis-
cussed in Section 3.5i
a. Method A Isopleth Maps (S02 and TSP Only)
An adequate number of stations can be approximated from in-
formation on existing levels of pollution as a function of the area
of the region. Isopleth maps resulting from diffusion models
(See Appendix D) are useful 1n this determination. At the present
time, use of this mathematical approach 1s limited to the design of
the monitoring networks for suspended partkulates and sulfur dioxide.
The equation for estimating adequate network size relates the
number of stations to the degree of pollution and the land area of
the region. It 1s based on the fact that more stations are needed
in zones where ambient air pollutant concentrations may be expected
to exceed the ambient air quality standards. The equation considers
distinct areas: the area, X, where the pollution levels are higher
than the ambient air quality standard; the area, Y, where pollution
-------
B-2
levels are above background but lower than the standard; and the area,
Z, where existing concentrations are at background levels. In these
equations all air quality data are expressed In terms of annual averages.
The total number of samplers, N, required for the entire region 1s ob-
tained by summing the estimated numbers of samplers for each of the three
subareas:
N = Nx + Ny + Nx
The subareas are described as follows:
N¥ = 0.0965 Cm " Cs X
f
S
Ny = 0.0096 Cs " Cb Y
~
Nz = 0.0004 Z
Where:
Cm = Value of maximum Isopleth (with a contour Interval of 10)* pg/m3
Cg = Ambient air quality standard, ug/m annual average
C^ = Value of the minimum Isopleth (with a contour Interval of 10),
o
n g/m annual average
X = Area wherein concentrations are higher than ambient air 'quality
standard, km
Y - Area wherein concentrations are above background but less than
2
ambient standard, km
2
Z = Area wherein concentrations are at background levels, km
Estimated background values for total suspended participates and S02
-------
B-3
TABLE 1
TSP AND S02 VALUES FOR NONURBAN BACKGROUND TERM
(yg/m3)
Proximate3 Intermediate Remote0
Total suspended 45 40 20
particulate
Sulfur dioxide 20 • 10 5
Proximate values based upon NASN stations in the following
states: Connecticut/ Delaware, District of Columbia, Maryland,
Massachusetts, New Jersey, New York, Pennsylvania, Rhode Island.
Intermediate values for all other states.
Remote values based upon NASN stations.in the following states:
Colorado, Idaho, Minnesota, Montana, Nebraska, Nevada,
New Hampshire, New Mexico, North Dakota, Utah, Wisconsin,
Wyoming.
-------
B-4
for use when Isopleth Information 1s not available are listed 1n Table 1.
Use of these equations requires the division of the region Into three
zones on the basis of Iso-lntenslty lines representing the ambient air
quality standard and the background value appropriate for the region. The
land areas of each zone are determined from the Isopleth map, as are the
maximum and minimum concentrations 1n the region. The above equations
should not be used to estimate the numbers of background stations where
regions encompass large unpopulated areas. No more than two or three
background stations should be necessary 1n any region.
The equation for determining number of stations was derived from
an analysis of the relationship between pollution levels and patterns,
geometric distribution of sources, meteorology, and land area 1n the
National Capital Interstate A1r Quality Control Region. The equation
was applied to several other cities 1n the United States with various
population and pollutant distributions. As mentioned earlier, 1t 1s
applicable only to S0« and TSP networks.
An application of the above to Washington, D.C. data for suspended
partlculate matter yields the following:
Cm = 100 g/m3
Cs = -75 g/m3
Cb = 40 g/m3
X = 417 Km2
Y = 3889 Km2
Z = 2231 Km2
-------
B-5
N¥ = 0.0965 (100 - 75) 417
^ •••••^••pMiWHMMir
= 13
N = 0.0096 (75 - 40) 3889
y ^__
= 17
Nz = .0004 (2231) ;
= 1 . ' ' . ' ' ' .
N = N + N + N
" Jr , 2 - '
= 13+17+1
= 31
b. Method B Multiplication Factors (S02, TSP, Oxidants, N02)
If past air quality and/or model Information are not available, then the
adequate number of monitoring stations for partlculates, sulfur dioxide,
nitrogen dioxide, and oxidants can be determined by adjusting the mini-
mum number through a multiplication process with factors which influence
air quality levels discussed 1n Section 3.1. The procedure is outlined
below:
Np = (TF x CF) X Mp
where N = adequate number of stations required for a given pollutant
Tp = Topography Factor
Cr = Climatology Factor
r /
Mp = Minimum number of monitoring stations for a particular
pollutant (from Table 1 Section 3.2)
-------
B-6
Regime
Valley-ridge
Hilly-
mountainous
Shoreline
Level or
gently rolling
TOPOGRAPHY FACTOR
Description Factor
Continuous contours 1.8
of greater than 300
feet between a valley
and a ridge within a
mile of the horizontal
distance
Terrain elevations 1.5
greater than 800-1000
feet between hills or
mountains and valley
f 1 oor
Bodies of water of a 1.2
size at least equal
to the Great Salt Lake
No marked contours 1.0
or shorelines
These topographic factors are relative numbers based on the factors
influencing air quality discussed in the previous section for each of the
regimes listed. The description used should describe the urban area of
the AQCR or where the worst pollution areas are located rather than the
entire sampling area to be covered. It may be necessary to subdivide the
AQCR if the topographic features are significantly variable.
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B-7
CLIMATOLOGY FACTOR
Atmospheric Area5 Short-Termb Long«Tertnc
California-Oregon 2.0 1.6
coastal
Washington coastal 1.4 1.4
Rocky Mountain 2.0 1.1
Great Plains 1.0 1.0
Great Lakes-Northeast 1.1 1.4
Appalachian 1.6 1.4
Mid-Atlantic coastal 1.4 1.0
South Florida 1.0 1.0
Tropical 1.0 1.0
South Coastal Alaska 1.5 1.5
North and Central Alaska 2.0 1.8
Note: The use of the short and long-term factors should be according
to the particular pollutant for which the network is being designed.
Pol1utant Faetor
Nitrogen dioxide Long-term
Sulfur dioxide Short-term; long-term
Suspended Short-term; long-term
particulates
Oxidants Short-term
For sulfur dioxide and particulates, the choice of factor should
be based on which one is quantitatively greater in the particular
Atmospheric Area being considered.
a See Appendix A
b Based on isopleths of total number of forecast-days of high meteorological
potential for air pollution in a 5-year period. (Holzworth, AP-101, 1972
(Fig. 71))
c Based on a consideration of ranking average ventilation factors (Holzworth,
AP-101, 1972 (Table 3))
-------
B-8
As an example} the determination of an adequate number of sulfur
dioxide samplers for a Region with the following characteristics 1s as
follows:
Population = 7,800,000
Topography = shoreline
Atmospheric Area = Mid-Atlantic coastal
TF (shoreline) =1.2
Cp (Mid-Atlantic coastal) = 1.4 (short-term 1s higher)
Mp (sulfur dioxide) = 6 + 0.05 per 100,000 population
= 6 + 0.05 (78)
= 10
= (1.2 x 1.4) x 10
sulfur dioxide _ ,,
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c-i
APPENDIX C
SCREENING PROCEDURE* FOR DETERMINING THE NECESSITY
OF MONITORING ELEVATED POINT SOURCES
The screening procedure In a step-by-step manner 1s as follows:
Steps 1 through 4 are used to determine plume rise for various wind
speeds. If there Is more than 1 stack, each stack should be considered
separately through Step 8. Step 5 determines the effective height of
emission for the various wind speeds. Steps 6 through 8 determine
the maximum 1-hour concentration from the source and Step 9 estimates
the concentration for a slightly longer averaging time. Step 10 es-
timates the total maximum concentration by adding the background to
that due to the point source. Step 11 compares the estimated
maximum concentration with the standard and the result Indicates
whether or not the source exceeds the standard. The required
source Information 1s:
Q » maximum emission rate at peak production of the plant
for the pollutant considered* g sec~
h « physical stack height above the ground, m
d « Inside top diameter of the stack, m.
vs= stack gas exit velocity, m sec"
TS» stack gas exit temperature, °K : .
* Abstracted from "A Sample Screening Technique for Estimating the
Impact of a Point Source of A1r Pollution Relative to the A1r
Quality Standards," D^B. Turner and E.L. Martinez, EPA, April 1973.
this paper Is'still In draft form and has not been offi-
cially cleared, therefore, this procedure 1s interim and
subject to some later revision.
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C-2
Step V
Find stack gas volume flow from:
Yf = 0.785 v$d2
Step 2
Find the buoyancy flux parameter from:
F* 3.12 V s
T. - 293
f V
Step 3
Find the product of plume rise times wind speed by the
following:
If F 1s less than 55:
AH. • 21.4 F 3/4 .
where AH 1s plume rise, m
and u 1s wind speed, m sec ~
If F 1s greater than or equal to 55:
AH.u •• 38.7 F375
Step 4
Determine the plume rise, H, for each of these five wind
speeds: 0.5, 1.0, 2.0, 3.0, and 5.0 m sec*
These are found from: /
AH • (AH.u)/u
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C-3
Step 5
Find the effective height of emission, H, for each of the
above wind speeds. H 1s 1n meters.
H - 4H + h
Step 6
For each of the 5 H's corresponding to the 5 wind speeds
estimate xu/Q from Figure 5 as a function of H,
Alternatively, each xu/Q can be estimated from the equation:
xu/Q • a Hb
where a and b are as given in the following table for the appropriate
range of H.
Range of H
(meters)
10 to 20
20 to 50
50 to 100
100 to 2000
a
0.05405
0.07537
0.03612
0.02164
b
-1.587
-1.698
-1.510
-1.399
Step 7
For each xu/Q found 1n Step 6, determine the x/Q corresponding
to each wind speed as follows:
x/Q B xu/Q
u . '
If there Is more than one stack being considered, Steps 1
/
through 8 must.be applied for each stack separately. The values
-------
found for each stack In Step 8 are then added together. This value
of the concentration can be considered a maximum for the 1-hour
averaging time.
Step 8
Using the maximum of the five x/Q values found in Step 7,
find the concentration. xpn» due to this point source from:
Xph(ugnf3) - 106QX/Q
Step 9
If the above value Is to be compared with an air quality
standard having a different averaging time, determine the xp by
multiplying xph by the appropriate value 1n the following table.
-------
C-5
Figure 1. Maximum xu/Q as a Function of Effective Height of
Emission, H, where x is Concentration, u is Wind
Speed, and Q is Emission Rate.
10
10-3
10
JiJLJUJJ-
S I. 7 >.
-------
C-6
Figure 1, Continued
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-------
C-7
Averaging Time Correction
«
1 hour 1.0
3 hours 0.75
24 hours 0.25
Step 10 ,
Find the quantity x,^. where B 1s the maximum expected back-
ground concentration of the pollutant considered for the averaging
time and frequency of occurrence of the standard within a 10 kilometer
radius of the source considered,, that Is, due to other sources than
the one being considered, and xp 1s the maximum short-term concentra-
tion from the point source from Step 9.
Step 11
^•5
S 1s the short-term air quality standard (pg m" ). If y^x 1s
less than 1/2 S, 1t is probable that the source considered will not
cause concentrations exceeding the short-term air quality standard
and therefore source monitoring 1s not required.
If x^x 1s more than 2S, It Is almost certain that the source
concerned will cause concentrations exceeding the short-term standard
and therefore source monitoring should be undertaken.
•<
If Xjjujj Is more than 1/2S but less than 2S, more detailed analysis
of the Impact of this source upon air quality should be performed to
determine 1f source monitoring Is required.
-------
C-8
An example of this procedure 1s as follows:
A source emits sulfur dioxide at a rate of 1200 grams per
second from a stack which 1s 100 meters high and has an Inside
diameter of 3 meters. The stack gas velocity 1s 7.6 meters per
second and the stack gas temperature 1s 420°F (489° Kelvin). Sho
Should monitoring be recommended for this plant?
* • •
a. Compute the stack gas volume flow from:
V" 0.785 V$d2 « (0.785) (7.6) (3)2 » 53.7 m3/sec
b. Compute the buoyancy flux F•» 3.12 V /I- a\. Assume ambient
temperature 1s 68°F = 293K. F = (3.12) (§3.7) 0- |ff) =
67.2 m4/sec3
c. Since F 1s greater than 55, AH.u • 38.7 F3/5.- (38.7)(67.2)3/5*
483 m2/sec
d. Determine plume rise for each of five wind speeds:
(1) u « 0.5, AH « (AH.u)/u - 483/.05 « 966m
(2) u « 1.0, AH « 483/1 -483m
(3) u « 2.0, AH » J83/2 - 242m
(4) u » 3.0, AH • 483/3 - 161m
(5) u = 5.0, AH = 483/5 » 97m
e. Find the effective height of emission (plume height) H » AH + h,
*
»
for each wind speed
(1) ' 966 + 100 • 1066 '
(2) 483 + 100 » 583
(3) 242 * 100 • 342
-------
C-9
(4) 161 + 100 • 261
(5) 97 + 100-197
f. Estimate xu/Q from Figure 4 for each wind speed, and divide by u
1n each case to get x/Q:
(1) (1.25-10~6)/(0.5) » 2.5 X 10~6
(2) (2.9'10^6)/(1.0) - 2.9 X 10"6
(3) (6.2'1(T6)/(2.0) - 3.1 X 10~6
(4) (9.5-10"6)/(3.0) « 3.1 X 10"6
(5) (13.6'10~6)/(5.0) " 2.7 X 10~6
g. The maximum x/Q In the above step Is 3.1 X 10 . Using this
value, and a Q of 1200 g/sec. » Cx/Q](Q) B (3.1 X 10"6j (1200)
« 3700'1 0"6g/m3 " 3700 yg/m3.
Since this value (3700) 1s more than 1/2S (or 1300) but less
than 2S (or 5200), a more detailed analysis of the Impact of this
source should be performed for air monitoring purposes.
-------
o-r
APPENDIX D
COMPUTERIZED ATMOSPHERIC DIFFUSION MODELS
AVAILABLE FROM EPA
Numerous variations of atmospheric diffusion models exist which may
be utilized in the design of air quality monitoring networks. The A1r
Quality Display Model (AQDM) 1s suitable for the long-term, urban appli-.
cations involving sulfur oxides and particulate matter. Other models
are available including those in the EPA UNAMAP system designed for inter-
active remote computer terminal operation and are readily available to
EPA Regional Offices. The latest UNAMAP catalog of models, with a brief
description of each, is presented below. A comprehensive air quality
modeling guideline is presently being developed by the Monitoring and
Data Analysis Division.
There are no models which adequately describe the source-receptor
relationship for photochemical air pollutants. A few models of this
type are under development and some may be available in the near future.
-------
D-2
UNAMAP - USERS NETWORK FOR APPLIED MODELING OF AIR POLLUTION
Contact: Dr. Ron Ruff, Chief, Computer Techniques Group
Division of Meteorology
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Phone 919/549-4566
CATALOG OF PROGRAMS as of 06/01/73
APRAC - A short-term Urban Diffusion Model that calculates the automotive
contribution to Carbon Monoxide. The model was developed by Stan-
ford Research Institute (SRI). A 120 page manual 1s available on
the" model.
HIWAY - A model that calculates a pollutant concentration In the vtdrvfty
of a roadway. The model 1s self-documenting.
PTMAX - An Interactive program which performs an analysis of the maximum,
short-term concentration from a point source as a function of
stability and wind speed.
PTDIS - An Interactive program which computes short-term concentrations
downwind from appoint source at distances specified by the user.
PTMTP - An Interactive program which computes, at multiple receptors,
short-term concentrations resulting from multiple point sources.
CDM - The Cllmatologlcal Dispersion Model (COM) determines long-term
(seasonal or annual) quasi-stable pollutant concentrations at any
ground level receptor using average emission rates from point and
area sources and a Joint frequency distribution of wind direction,
wind speed, and stability for the same period. This model differs
from the A1r Quality Display Model (AQDM) primarily In the way In
which concentrations are determined from area sources, the use of
Sriggs' plume rise, and the use of an exponential Increase In wind
speed with height dependent upon stability. CDM uses a separate
da tar. set for the area of Interest.
The CDM model requires a source listing for a user to understand the
data set formats. Manuals for the above models are 1n preparation
and should be available by December 1973. TAPRAC Manual ts now
available).
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