DRAFT
GUIDELINE  SERIES
          OAQPS NO.  1.2-012
            September 1975
           GUIDANCE FOR
    AIR QUALITY MONITORING NETWORK
     DESIGN AND INSTRUMENT SITTING
             (REVISED)
  VS. ENVIRONMENTAL PROTECTION AGENCY
    Office of Air Quality Planning and Standards

      Research Triangle Park, North Carolina

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                                                     DRAFT
                 GUIDANCE  FOR
        AIR QUALITY MONITORING NETWORK
         DESIGN AND INSTRUMENT SITING
                  (REVISED)
             OAQPS Number  1.2-012
              September 1975
    Monitoring  and  Data Analysis Division
Office of Air Quality Planning and Standards
       ENVIRONMENTAL PROTECTION AGENCY
   Research Triangle Park, North Carolina

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                              CONTENTS




Section                                                           Page




I         GENERAL                                                 1-1




          1.   INTRODUCTION                                       1-1




               1.1  Purpose and Scope                             1-1




               1.2  Document Organization                         1-4




          2.   MONITORING OBJECTIVES                              1-5




               2.1  Definition of Objectives                      1-5




               2.2  Typical Monitoring Objectives                 1-8




II        BASIC MONITORING NETWORKS                               II-1




          1.   DESIGN OF THE NETWORK CONFIGURATION                II-1




               1.1  Network Size                                  II-2




               1.2  Factors Influencing Network Design            II-5




               1.3  General Patterns of Basic Networks            11-11




               1.4  Additional Guidance                           11-21




          2.   INSTRUMENT SITING AND PROBE EXPOSURE               II-22




               2.1  Site Selection                                11-22




               2.2  Probe Placement                               11-26




               2.3  Additional Guidance                           11-31




          3.   NETWORK OPERATION                                  11-35




               3.1  Monitoring Equipment Selection                11-35




               3.2  Operating Procedures                          11-37




III       REFERENCES                                              III-l
                                ii

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                         CONTENTS (continued)




Supplement




A         ADDITIONAL CO SITING GUIDANCE (attached)




B         POINT SOURCE MONITORING (forthcoming)
                                iii

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                               FIGURES

No.                                                                Page

II-1     Atmospheric Areas of the Contiguous United States          II-7

II-2     Mean Daily Solar Radiation (Langleys), Annual              11-10

II-3     Typical Chronology of Photochemical Smog Formation
         During the Day                                             11-17

II-4     Seasonal Differences in NO and N0? Peaks                   11-18

II-5     Averages of The 1969-1970 Annual Maximum Hourly CO
         Concentrations and Slant Distances at Air Monitoring
         Stations                                                   11-24

II-6     Schematic of Cross-Street Circulation in Street
         Canyon                                                     11-25

II-7     The Vertical Distribution of CO Concentration On A
         Street With Traffic Volume of 1,500 Vehicles/Hour          11-29

II-8     Horizontal CO Patterns At Three Heights Near An
         Intersection                                               11-30

II-9     Ninety-five Percent Confidence Intervals About The
         Annual Primary Standard for TSP For Various Sampling
         Frequencies (Assume the Standard Geometric Deviation
         Equals 1.6)                                                11-39
                                iv

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                               TABLES

No.                                                                Page

1-1      General Monitoring Objectives                              1-7

1-2      Matrix of Monitor Orientation and Data Uses                1-9

1-3      Monitoring Objectives By Pollutant                         1-10

II-1     Regulatory Minimum Number of Monitoring Sites              II-4

II-2     Atmospheric Areas of the United States                     II-8

II-3     Distribution of Continuous and Bubbler S02                 11-12

II-4     Comparison of Hi-Vol Data At Two Different
         Heights - Franklin Institute, Philadelphia                 11-27

II-5     Summary of Guidelines For Station Siting and Probe
         Placement                                                  11-32

II-6     Probability of Selecting Two or More Days When
         Site Exceeds Standard                                      11-40
                                v

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                              SECTION I
                               GENERAL

I.I  INTRODUCTION

1.1.1  Purpose and Scope

The purpose of this document is to provide the Regional Offices of the
Environmental Protection Agency and the various State and local air pol-
lution control agencies with guidance and assistance relating to the
technical problems associated with the design of air quality monitoring
networks and the selection of sites for instrument placement.  It con-
solidates, updates, and expands the information contained in several
previous documents:
    •   Guidelines:  Air Quality Surveillance Networks,
        Environmental Protection Agency, AP-98, May 1971.
    •   Guidelines for Technical Services of a State Air
        Pollution Control Agency - Appendix A, Environmental
        Protection Agency,  APTD-1347,  November 1972
    •   OAQPS Guideline Series 1.2-007, Air Quality Monitoring
        Interim Guidance, August 1973.
    •   OAQPS Guideline Series 1.2-012, Guidance for Air
        Quality Monitoring Network Design and Instrument
        Siting, DRAFT VERSION, January 1974.

It does not deal specifically with the issues of quality assurance in the
operation of air quality monitoring networks, although these issues are
closely related to the current topic;  for guidance on these issues, the
reader should consult the following documents:
                                1-1

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    •   Quality Control Practices in Processing Air Pollu-
        tion Samples, Environmental Protection Agency,
        APTD-1132, March 1973.
    •   Guidelines for Development of a Quality Assurance
        Program? Environmental Protection Agency, EPA-R4-73-028,
        a through e, June 1973.
Although the discussion in this document is concerned primarily with the
six pollutants for which air quality standards have been set, and with
associated meteorological monitoring, the principles on which it is based
are equally applicable to monitoring programs directed at other pollutants.

The ultimate purpose of providing this document is to further the goal of
increasing the usefulness of, and the compatibility among the various
sources of, ambient air quality data throughout the country; the use of
this information by States and EPA Regions should lead to a more con-
sistent, more reliable national data base that will minimize the risk of
making inappropriate policy choices or of designing control strategies that
are either inadequate or unduly stringent.

This document, however, is not intended to, and indeed could not, supplant
the need for the States and Regional Offices to develop and maintain
expertise in these matters on their own technical staffs.  The issues of
network design and instrument siting involve difficult tradeoffs between
air quality information needs and available resources, and between demands
for data representativeness and instrument site availability.  There is
no reasonable way that specific guidance covering all the possible aspects
of these complex tradeoffs can be provided in detail by a document of this
type.  On the other hand, it is equally clear that the compatibility of the
resulting data requires a large degree of adherence to some consistent set
of guidelines, so that the practical, close-at-hand problems with re-
sources and site availability do not totally dominate the necessary
decisions.
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Accordingly, this guideline document has been prepared not as a pre-
spective policy document, but rather as a technical document, intended to
identify the problems that typically arise in the process of network
design and instrument siting, and to offer the generally-accepted levels
of resolution of these problems.  It primarily provides the technical
information required to permit the State and Regional Office personnel
responsible for these issues to make intelligent, informed decisions based
on a reasonable knowledge of the consequences.

The reader will likely note that the tone of this document implies that
much more consideration, in both manpower and monetary resources, should
be applied to the issue of siting monitoring facilities than is currently
the common practice.  This is a deliberate element of philosophy under-
lying this guidance material.  It is considered inconsistent to undertake
a monitoring effort involving resources in the tens of thousands of
dollars without investing the far smaller effort involved in resolving
the issues of proper siting of the monitoring instruments.

It must be emphasized that this material is guidance, to be applied with
judgment, not a set of rigid rules to be applied in isolation.  If an
existing monitoring site does not meet the placement criteria contained
herein, that does not in itself mean the data from that site cannot be
used for various purposes.  Rather, it merely means that consideration of
the effects of the siting must be included in the interpretation of data
from the sites.  If there are valid reasons for siting a monitoring in-
strument outside the bounds recommended here, they can and should take
precedence, and sites should not be arbitrarily moved.  On the other hand,
if there are no compelling reasons for the existing siting, gradual
changes toward closer conformance with the guidelines are appropriate, in
order to reduce the overall national range of variation in siting
parameters.

Because the technical information available to bring to bear on these
problems is not completely adequate, nor as quantitative as would be

                                1-3

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desirable, the Monitoring and Data Analysis Division of OAQPS has under-
taken an extensive program to develop more quantitative data, especially
on the effects of site exposure parameters.  As this effort progresses,
and such information becomes available, this document will be expanded
and revised as appropriate.

1.1.2  Document Organization

The variety of reasons and purposes for ambient air quality monitoring
have understandably led to a variety of different types of networks
relating to one or another circumstance, each with its own special needs
and special sets of problems.  To accommodate these differences as meaning-
fully as possible, this guideline considers three general types of
monitoring as distinct situations, although it is of course recognized
that there will be some circumstances where monitoring efforts fall into
gray areas between these categories.  The three major types of monitoring
considered are:
    •   Basic, fixed, ongoing monitoring networks
    •   Monitoring systems around major single sources
    •   Monitoring for indirect source review and planning

In this categorization, a basic, fixed, ongoing network is a network
deployed throughout a significant geographical area, and intended to pro-
vide consistent, ongoing data over a period of many years.  Although such
networks are labeled "fixed," this is done only in a relative sense, to
distinguish them from shorter-term special purpose efforts.  The network
design and siting decisions in such a network are not immutable; and in
fact they must be reevaluated periodically as existing air quality patterns
become known and as new land use and population growth and development
occurs.  In contrast to the basic, ongoing network, the other two types
of networks are generally developed for specific shorter-term purposes,
and are usually much more intensive in both time and space.  Each is
                                1-4

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intended to monitor the air quality impact from a specific source, rather
than the overall air quality from a receptor viewpoint.

Monitoring for such purposes as transportation control planning and air
quality maintenance planning, which are basically components of the on-
going implementation planning process, require essentially ongoing
monitoring efforts, and hence are considered part of the basic fixed net-
work.  The fixed network may be supplemented by mobile or portable type
monitoring for short-term surveillance of the local impact of specific
control tactics.

This document discusses the objectives of monitoring, in the context of
all three categories, and the way in which the careful definition of
objectives can assist in making the necessary design and siting decisions,
and then considers the first of the three major categories of monitoring
listed above, the basic fixed network.  Supplement A contains additional
detailed guidance on CO siting, summaries of which are contained within
this volume.  Supplement B, which is still in preparation, will present
a discussion of monitoring around isolated point sources.
1.2  MONITORING OBJECTIVES

1.2.1  Definition of Objectives

It is generally agreed that the design of an ambient air quality monitoring
network should ultimately depend on the purpose of the network; that is,
on the reasons for which the monitoring is to be conducted, or the pur-
poses which the data are intended to serve.  Although this is a commonly
stated goal, its implementation in practice has generally been difficult.
When considered carefully, this difficulty is usually seen to result from
variations in the detail with which the objectives are specified.  The
clear, policy-oriented goal that is provided by the Clean Air Act, for
                                 1-5

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instance, is usually too general to be of specific help in planning
monitoring operations, while the specific questions like "How many times
do the ambient levels exceed the standards?" frequently seem too prosaic
or too narrow to be considered "objectives."

In order to clarify this difficulty, and to provide a framework within
which our thinking about monitoring objectives might be structured, it
is proposed that monitoring objectives can be conveniently and accurately
thought of as occurring in three levels of detail:
    •   Fundamental goal of monitoring
    •   General monitoring objectives
    •   Detailed requirements of data base

1.2.1.1  Fundamental Goal of Monitoring

The basic, fundamental goal of ambient air quality monitoring efforts, as
with other air pollution control efforts, is the protection of human
health and welfare under the Clean Air Act.  Since this is far too general
to be of specific help, more definitive objectives have been stated as
EPA regulations, and in further guidance, such as this document.  All
this other information, however, is still rooted in the basic purpose
of the law, which should not be overlooked in the process of making net-
work design decisions.

1.2.1.2  General Monitoring Objectives

This category includes those statements about the purpose of monitoring
that are derived from the basic fundamental goal, but which are not de-
tailed specifications of needed data.  They are derived from the basic
goal in the sense that they represent judgments about what is required to
protect human health and welfare in an operational sense.  These objec-
tives are typically most relevant to the decisions on the station-location
aspects of network design,  as opposed to the more detailed data
                                1-6

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 specifications, which are more relevant to decisions on sampling frequency
 and other operating parameters of the network.  The list in Table 1-1 il-
 lustrates the  level of definition meant to be associated with this
 category; it includes the objectives of this type that are believed to be
 widely meaningful on a national scale.

               Table 1-1.  GENERAL MONITORING OBJECTIVES

  •  Provide data for research
  •  Provide data for air quality planning efforts
  •  Provide data for emergency episode prevention
  •  Monitor time trends and patterns
  •  Monitor source compliance with regulations
  •  Ascertain attainment and maintenance of NAAQS (population exposure)
  •  Determine impact of specific proposed or constructed facilities or
     source concentration
  •  Provide data to support enforcement actions

 1.2.1.3  Detailed Requirements of Data Base

 The most detailed type of monitoring purposes are those that specify the
 precise data needed for a specific purpose; e.g., "the number of days
 particulate levels exceeded the 24-hour standard."  These detailed
 specifications of data requirements, when they can be precisely estab-
 lished, are of great value for planning purposes;  primarily for
planning the operational aspects of a network rather than the overall
configuration or instrument siting aspects.  In general, these data needs
will differ with the pollutant under consideration, and they may well
differ with the changing nature of the pollution problems from one part
of the country to another or from one AQCR to another.
                                1-7

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1.2.2  Typical Monitoring Objectives

It is apparent that in general it is the monitoring objective, the second
level of detail of the three above, that primarily affects the location of
sites and the placement of sensors.  It is not the purpose of this document
to prescribe, as a matter of policy, what the objectives of a monitoring
program should be or what priorities various objectives should have.  How-
ever, some discussion of typical objectives and the structures into which
they fall is necessary in order to illustrate the way in which the general
objectives are refined Into more specific decisions with respect to
monitoring sites and the way in which careful consideration of these ob-
jectives can assist in the determination of definition of specific data
needs.

One useful structure that includes the objectives in Table 1-1 can be de-
veloped by considering various combinations of the location, or orienta-
tion, of a monitoring effort and the intended use of the data from that
effort; this matrix-type structure is presented in Table 1-2.  Clearly, a
monitoring site can be primarily directed at pollutant sources, at pol-
lutant receptors (population), or at a background situation where neither
sources nor population is generally present, although for some purposes
this three-way classification might be usefully subdivided.

The subdivision on the other dimension of the matrix in Table 1-2, the sub-
division of data uses into compliance, trends, and planning, is somewhat
less clear-cut.  To focus on the essentials of station placement, the three
categories were defined on the basis of the fundamental conceptual require-
ments made of the data by each intended use.  Thus, attainment and mainte-
nance of standards involves primarily the absolute magnitude of the re-
sulting data, while trend evaluation requires only that the data be
consistent over time.  Most planning purposes require in addition, joint
information over various spatial points or for several pollutants.
                                 1-8

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Table 1-2.  MATRIX OF MONITOR ORIENTATION AND DATA USES
Data uses
Standards
attainment
and
maintenance
Trends
Air quality
planning
Monitor orientation
Source-oriented
• Enforce property-
line regulations
• Monitor control
progress trends
of grouped
sources
• New source per-
mit review and
planning
Population-oriented
• Peak population
exposure
• Typical
population
exposure
• Trends in
exposure
• Geographic pat-
tern for control
strategy
planning
Background


• Control strategy
planning
• Determine urban
impact

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reasoning behind the common practice of monitoring for the two pollutants
at the same sites.  Similarily, the general lack of similarity among the
other gaseous pollutants indicates that each will require separate con-
sideration, rather than routinely placing all gaseous instrumentation
together.

These latter points illustrate the type of conclusions concerning network
configuration that can be drawn from various approaches to structuring the
objectives.  The first four rows and to some extent the last row of
Table 1-3 are the objectives that are normally intended to be met by the
basic fixed network, the others being relevant to source-oriented networks.
Similarly, in Table 1-2, the source-oriented column would be generally
assigned to specific source-oriented networks, other than possibly an
isolated single fixed site in a heavy industrial area, which might be used
to observe air quality trends admist a complex of sources.  Based on con-
sideration of these two structures, several different types of stations
(Peak, Neighborhood, and Background) have been defined for each of the six
major pollutants, primarily for purposes of discussion throughout this
document:
    •   Peak Station - Located at one of the points within the
        Region where the highest concentrations and exposures
        are expected to occur.
    •   Neighborhood Station - Located to typify a broad area of
        uniform land use, not necessarily residential, but in-
        cluding also homogeneous industrial or commercial areas.
    •   Background Station - Located in nonurban or rural areas
        to provide information on levels of a pollutant trans-
        ported into a Region.
                                 1-11

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                              SECTION II
                      BASIC MONITORING NETWORKS

Basic fixed monitoring networks, in the context of this discussion, are
those monitoring systems that are directed at the overall, ongoing,
regional problem of guiding the federal-state-local pollution control
programs designed to attain and maintain the National Ambient Air Quality
Standards.  This includes the basic network established in support of the
original State Implementation Plan, and any extensions and expansions
subsequently made in conjunction with transportation control planning,
air quality maintenance planning, prevention of significant deteriora-
tion, and so on, as these latter efforts are essentially just SIP
extensions for specific purposes.

The ongoing development of a permanent air quality monitoring network
involves the determination of the number and location of sampling sites,
selection of appropriate instrumentation, determination of the frequency
and schedule of sampling, and establishment of instrument and probe siting
criteria.  These four basic elements of any air quality monitoring net-
work are discussed separately in subsequent portions of this section.

2.1  DESIGN OF THE NETWORK CONFIGURATION

The configuration of an air quality monitoring network involves two ele-
ments:  the number of sensors or sampling sites of various types, and
their geographical location.  Under differing circumstances, decisions
on the two elements can be made in either order; an overall number of
sensors or sites may be selected, based on a criterion such as resource
                              II-1

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availability, and then distributed geographically, or specific sites may
be selected first, based on a criterion such as the need for the data,
with the aggregate number of sites then being just the total number of
sites selected.  In the past, and to some extent still at the present
time, the first approach has been necessarily taken, and approaches to
determining network size are discussed herein.  In the longer term,
however, it is considered appropriate that actual data needs be the ulti-
mate determinant of network size, and that the availability of resources
should affect only the speed with which that ultimate size is reached.
With this approach, one considers the various requirements of the network,
establishes sites to provide the required data, and lets the size of the
network be whatever it turns out to be.  In this way, the relevant param-
eters of the area - the overall size, the distribution of "unique" pockets
of sources and receptors, the topography, etc., - are all taken into
account.

2.1.1  Network Size

Historically, when the national control effort under the Clean Air Act
began, emphasis was on developing not only new networks but also the
resources, both manpower and monetary, to support them.  Consequently, it
was necessary that networks be sized directly or indirectly in relation
to the resources available, and the sites then distributed with as much
consideration of sources, topography, etc., as was possible.

The Environmental Protection Agency Regulations (40 CFR 51.17)   detailing
the requirements for a State Implementation Plan include specification of
a minimum number of monitoring sites in the AQCR as a function of the
AQCR population and the priority classification assigned to it for each
criteria pollutant.  Population is a meaningful index for determining the
number of sites because geographic area, fuel use, industrial capacity,
and many other relevant parameters which affect air quality are roughly
correlated with population.
                               II-2

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Ihese minimum regulatory requirements are tabulated in Table II-1; they
are designed to meet the bare minimum essential requirements of a net-
work, in the context of the resource situation of the early 1970's.  It
is generally recognized that, in the present context, these minimum
requirements are not adequate in every urban area or AQCR, nor are they
necessarily adequate for proper conduct of those implementation planning
responsibilities that have arisen since the original SIP planning pro-
cess.  For example, in some AQCR's carbon monoxide and oxidant monitoring
is inadequate for control planning purposes, and the geographical extent
of monitoring in relatively unpolluted areas is inadequate for use in
air quality maintenance planning.

As was indicated above, the ultimate determination of a monitoring net-
work configuration should be made on the basis of data needs to meet
specified monitoring objectives, rather than on the basis of any prior
determination of the number of sensors to be included.  However, recog-
nizing that for at least the next several years, resource availability
"ill ^mtinua ±o_QDera.te__ aga_constraint._ A reallocation of network
facilities may be more feasible than an increase in network size.
Redistribution of instruments from densely monitored urban core areas
to sparsely monitored suburbs and rural areas, necessitated by non-
degradation and air quality maintenance area considerations may be needed.
Trade-offs between too much monitoring in some areas, such as TSP and
S02, and too little monitoring for pollutants like ozone and CO may need
to be considered in the light of budgeting requirements.  However, the
monitoring budget should not be the overriding factor.  For example,  the
resources required to establish and operate additional CO and oxidant
stations should be considered not in isolation, but rather in light of
the resources required to develop,  promulgate, and implement (and possibly
litigate) a state implementation plan based on the data developed.
                                II-3

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-------
 2.1.2  Factors Influencing Network Design

 The  factors that are typically involved in estimating an adequate network
 size are of course also the factors involved in designing an ultimate
 network configuration as well, primarily climatological and topographic
 factors.  These factors are typically cited as meaningful in network
 design, but it is frequently difficult to make practical use of them.
 This is because they are significant primarily in the extremes, as noted
 below, rather than in the broad middle range prevalent throughout most of
 the  country.

 2.1.2.1  Meteorology and Climatology - The meteorological factors that
 have the greatest effects on ambient pollution concentrations are the
 horizontal wind (speed and direction, and the vertical distribution of
 both) and the vertical mixing structure (stability, mixing heights).  At
 most locations, however, these parameters vary significantly over time
 scales in hours and distance scales in tens of meters.  Thus, while they
 are  of significance in a number of air pollution areas, they are not of
 much help in the design of networks, which depends on longer-term average
 parameters.

 Dilution climatology is defined as the long-term average combination of
 those meteorotogical conditions that affect the interchange and disper-
 sion of pollutants over relatively large areas and long time intervals.
These factors,  the frequency,  persistence,  and height variations of wind
 speed and direction,  of stable (inversion)  layers of air, and of mixing
heights,  collectively provide  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,
 that exert their influence at that scale.   The relative frequency of
recurrence of short-term phenomena such as  stagnation episodes is also
 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 climatologies
                           II-5

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have been defined on a geographic basis for the contiguous United States.
They are illustrated in Figure II-l and described in Table II-2; interim
definitions for areas outside the contiguous United States in which
AQCR's have been designated are also included in Table II-2.  Figure II-2
presents isopleths of mean annual solar radiation which, in conjunction
with the dispersion characteristics of the various atmospheric areas,
relates to the potential for formation of photochemical pollutants.

As was noted above, these climatological factors are of primary signifi-
cance in the extremes.  The Great Plains Area has frequent high winds
which, coupled with the nature of the fuel use patterns, reduces concern
with S09; however, because of increased fugitive dust entrainment, par-
ticulate problems require increased concern.  Considering north-to-south
variations in solar radiation, it is apparent that the Southwest and the
Gulf Coast will have an accordingly greater concern with photochemical
oxidant levels.

2.1.2.2 Topography - The dispersion patterns in some sectors of an Air
Quality Control Region can be significantly altered by local topographi-
cal factors.  The most significant with respect to their influence on a
monitoring network are:
         Valley Effects - Valleys tend to channel the wind flow
         along their axis, restrict horizontal dispersion, in-
         crease the tendency for inversions to form,  and may
         cause aerodynamic downwash from stacks not  extending
         above the valley walls. "Air quality discontinuities
         between valley-ridge sectors often exist.   Thus, val-
         leys almost always need monitors in ;excess  of the
         requirement for level terrain.
                          II-6

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                                                60
II-7

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                   Table  II-2.    ATMOSPHERIC  AREAS OF  THE  UNITED  STATES
       Atmospheric area
                                             Extent of area
                                                                              Meteorological And topographical
                                                                                       characteristtca
California-Oregon coastal area
Washington coastal area
tocky Mountain area
Great Plains arta
Great Lakes Northeast  area
Appalachian area
                                 Extends about 20 to SO nlles  Inland  fro
                                 the Pacific Ocean.
 Extend* about 20 to 30 nlles  Inland  from
 the Puget Sound region, frora  which
 the eastern boundary extends  south-
 westward to the vicinity of Lon^view
 on the Columbia River and then west-
 ward to the coast.
Extends eastward froo the  California
Oregon and Washington coastal  areas  to
terminate as a north-south oriented
eastern boundary, essentially  core-
• pond ing to the 3.000 to -.,000 toot oean
sea level contour interval which  in gen-
eral defines the eastern oost  extension
of the major mountain ranges.   This
eastern boundary stretches troa the
Canadian border in Montana south-
vard through extreoe  eastern Colorado,
eastern N
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      Table   II-2   (continued).    ATMOSPHERIC AREAS  OF   THE  UNITED  STATES
       Atmospheric ar«a
                                               Extent of area
                                                                                 Meteorological and topographical
                                                                                          characteristic*
ttd-AtlantU araa
South rlorlds-Carlbbesn *raa
Hawaiian-Pacific ara«
Alaska* feclCia Knltl** av*a
Alaskan Baring Maritime  araa
Alaskan Arctic Maritlma  araa
Alaskan Continental  araa
Encompasses the Atlantic  coastal plain
from extreme southwestern Connecticut,
Including the New York City  and Long
Island region, southward  to  the South
Carolina border at the coastline, and
extends Inland to the  Appalachian araa.

Extends south from the DaytQns Beach
Cedar Key line to Include the aoothern
half of Florida. Puerto Rico, and ths.
Virgin Islands.
                                  Includes sll of the islands making  up
                                  the State of Hawaii, and the territories
                                  of Guam snd American Samoa.
Bound*4 by tVi* Unltsd  Statst-Csnsd* bor-
der to th« southeast)  the Chugateh Moun-
tain Range to the  north, and  the Aleutian
Range to the northwest.  As such this araa
Includes the Alexander Archipelago, the
coastal regions of the Gulf of Alaska,
Kodlsk Island, the Alaskan Peninsula, and
the Aleutian Islands.

Bounded by the southwestern and western
slopes of mountain'ranges and the ridge
line of the Sevard Peninsula.  As such,
the area Includes  the  coastal plateaus and
valleys of the southwest and western main-
land, the southern half of the Seward
Peninsula, and offshore island*.
                                  Bounded by the western slopes of mountain*
                                  from the Scward Peninsula  northward to tha
                                  Brooks Mountain Range  then eastward to
                                  United States-Canadian border.  As such,
                                  this area includes the northern half of tha
                                  Seward Peninsula,  the  coastal regions to
                                  tha north, and the tundra  region between
                                  the Brooks Range and  the Arctic Ocean.
                                  Bounded by tha inland portion of  tha
                                  Alaska-Canadian border to  the east and
                                  tha previously described Atmospheric Area
                                  boundaries to the north, south, and west.
                                                                              Shallow mixing depths,  less  frequent low-
                                                                              level stability and higher wind speeds
                                                                              are features of the dilution climate that
                                                                              distinguish this cosatsl  art*  fron thosa
                                                                              adjacent.
The climate of this ares Is  predominantly
tropical-marine In nature*   Atmospheric
stagnation Is practically nonexistent;
there 1* a small frequency of  low-level
stability; snd relatively good' vertlcsl
mixing prevails.

Relatively good ventilation; occasional
surface-based nocturnal  Inversion* In In-
land areas; persistent period* of stag-
nation are rare.

Undor th* influence o! Pacific Matitlma
weather patterns; relatively good ventila-
tion associated with frequent  storms; oc*
caatonal strong nocturnal inversions may
persist throughout the daytime during the
winter season; persistence of  such condl*
tlons Is not marked, however, because of
the frequency of atormlness.

Under the Influence of Bering Maritime
weather conditions.  Air Pollution cli-
matology varies from that of the Pacific
Maritime area because of less  frequent
storm activity and the resultant poten-
tial of greater persistence  of surface-
based inversions.  In spite  of difference*,
persistent stagnations are not frequent.

Under the influence of two,  seasonally-
oriented weather conditions; continental
during tha winter months when the ocean,
la frozen; maritime during the warmer
months when the ocean is partially free
of Ice.   Relatively high wind speeds pro-
vide good ventilation; the lack of solar
radiation in the winter  snd  cold maritime
winds during summer days result in the
highest annual frequency of  daytime
surface-based Inversions of  any of the
areas discussed here.

Under the influence of continental
weather conditions; sheltered  from mari-
time Influence by medium-to-high mountain
ranges on all sides; has the highest an-
nual frequency of nighttime, surface-
based inversions of any  of the adjacent
areas; low wind speed during the winter,
combined with extremely  persistent ground-
level inversions, gives  this araa tha most
restrictive pollution climatology of any
AoMspharlc Araa*
                                                    II-9

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11-10

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         Shoreline Effects - Airflow along shorelines undergoes
         frequent changes brought about by the changes in rela-
         tive temperature of the air and water.  Discontinuities
         and convergence zones in the dispersion patterns occur
         which indicate need for monitoring beyond required
         minimums.

         Hilly and Mountainous Terrain Effects - Complexities
         introduced by hills and mountains include disrupted
         airflow patterns, intersection of their interface by
         elevated plumes, induced mechanical turbulence and more
         frequent inversions in low-lying protected areas.
         Hilly and mountainous terrain usually increase the need
         for monitors.
In general, these concerns are greatest in the case of SC^ and particu-

lates which are often dispersed from major point sources.  They are of

lesser importance for automotive pollutants such as CO, or secondary
pollutants like CL and N0?.


2.1.3  General Patterns of Basic Networks


The overall configuration of a basic fixed network is primarily a function

of the purpose of the monitoring and the typical spatial distribution of

the pollutant under consideration.  It is important to initially design a

separate network for each pollutant under consideration, and only then to

consider whether  and to what extent the networks may be combined, with

sensors at common sites.  The following sections consider each pollutant

in turn, discussing the configuration of networks as they typically exist

and suggesting changes as appropriate.
                               11-11

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2.1.3.1  Sulfur Dioxide - The general configuration of a typical sulfur
dioxide network is one of roughly uniform distribution over the built-up
or populated portion of a Region, usually with a decreasing density in
the areas farther from the urban center.  One or more of the sites is
usually in the area of anticipated maximum levels, to monitor for the
attainment and maintenance of NAAQS, while the others serve to monitor
the exposure in neighborhoods (residential, downtown, commercial, etc.).
The primary goals of SO,, monitoring are all relatively well-served by
such a population-oriented network with a typical site-to-site distance
of at least 2 to 4 kilometers.  Typically regional S02 networks consist
of a mixture of continuous instrumentation and bubbler sites, and this
is considered appropriate; an acceptable distribution between the two
types is presented in Table II-3.  The use of continuous instrumentation
at more sites than indicated in Table II-3 at all sites,  is acceptable
(if somewhat expensive);  the use of less continuous and more bubbler sites
is not recommended.
                Table II-3.  DISTRIBUTION OF CONTINUOUS AND
                             BUBBLER S02 INSTRUMENTATION
                        Number of S02 Sensors
Total
1
2
3
4
5
6
10
15
20
25
30
35
40
Continuous
0
0
0
1
1
2
3
5
7
10
13
15
17
Bubbler
1
2
3
3
4
4
7
10
13
15
17
20
23
                              11-12

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This overall assessment of adequacy of SCL networks is based on  the
use of emission inventories to develop S02 emission density patterns
with special consideration given to any major industrial process S02  .
source that might cause significant deviations from a relatively smooth
geographic distribution.  In those few Regions with no significant S02
emissions, relatively less dense networks are adequate.

It  there  are significant industrial sources, or concentrations of  smaller
sources,  the network should include additional sites  to monitor  exposures
in  any adjacent residential areas.  In this context,  significant S02
source is intended  to refer to such as refineries, smelters, etc., that
have numerous emission points.  Major fuel-burning sources, such as power
plants, which have  only a very few elevated emission  points, should be
considered in the context of the discussions in Supplement B.  A third
situation requiring a significant deviation in the density of the  network
is  that of unusual  topography.  Major topographic features, such as hills
and valleys, that destroy the smooth uniformity of air quality patterns,
require additional monitoring to define the discontinuity.

In  general, current SCL state monitoring efforts are  typically adequate
in comparison to the monitoring efforts directed at other pollutants.  The
primary need in the near future will be for some reallocation of monitors
in the form of increased density in designated Air Quality Maintenance
Areas for S02 and around major isolated point sources, from the urban
core area or the CBD.
2.1.3.2  Suspended Particulate Matter - The general pattern of particu-
late networks is usually similar to that for S0«, in many cases consist-
ing of the same sites.  This is reasonable, since the two pollutants both
have a widespread multitude of small sources, frequently the same sources.
There are, however, differences in the nature of the two pollutants that
may lead to some differences in the network configuration.  Since entrain-
ment from the ground and other "fugitive dust" sources can be important
                               11-13

-------
for participates, the issues of actual siting become of greater importance
than with S0?.  In the past, a suspended particulate network that was
largely coincident with the S0~ configuration was generally considered
adequate.  However, as the traditionally important particulate sources
(industrial processes and fuel combustion, small coal-fired boilers) have
been eliminated or controlled, other types of sources (re-entrained urban
dust, rural fugitive emissions) have become of jajor concern.  Hence, a
reallocation of monitors to neighborhood and rural sites,  as opposed to indus-
trial peak sites, will be needed to understand these new problems and
develop appropriate control tactics.

2.1.3.3  Carbon Monoxide - In contrast to the case with S02 and particu-
lates, the general configuration of a typical CO monitoring network is
neither well-defined nor adequate.  In most cases, CO monitoring is con-
ducted at only three or four sites in an urban AQCR.  Because the measured
CO levels are very sensitive to the exact placement of the inlet probe,
the possibility of biased information resulting from this scarcity of
sites is greatly increased.

Designing a CO monitoring network  is, thus, quite complicated in com-
parison to other pollutants.  This is because of the nature of the NAAQS
for CO, and the differing circumstances in which they are typically vio-
lated.  As there is no long-term (annual or seasonal) standard for CO,
the objective of determining trends and patterns is of a good bit less
importance, and the objective of monitoring attainment and maintenance of
NAAQS is more complicated.  The issue is further complicated by the dif-
fering circumstances under which the 1-hour and 8-hour standard are typi-
cally  violated, which is determined by the interaction of the strong
daily cycle in CO source strength with the seasonal and daily cycles of
atmospheric mixing potential.  The 1-hour NAAQS for CO is typically vio-
lated under circumstances of maximum traffic during the morning rush hour,
often on mornings when a nocturnal radiation inversion has persisted
until the time of the rush hours.  Because they depend on having heavy
                                11-14

-------
 traffic  for a  short  period,  the peak  1-hour  levels  typically  occur  near
 points of major  traffic volumes.   In  contrast,  the  highest  8-hour CO  levels
 tend  to  occur  in the evening and overnight,  and may well  occur  quite  apart
 from  short-term  traffic peaks.  This  is due  primarily  to  differential cooling,
 down  slope drainage  and a  general  reduction  in mixing  height, commonly occuring
 in  the evenings  and  early  morning.

 It  is recommended that the overall CO network configuration should  involve
 sites of four  types  which  are discussed in detail and  prioritized in  Supplement f.
 These types are:
     •   Street  Canyon
            - Peak
            - Average
     •   Neighborhood
            - Peak
            - Average
     •   Corridor
     •   Background

As discussed in  Supplement A, there is generally little likelihood of
 totally defining an  area's CO air quality patterns with a monitoring  net-
work, because the variation  in CO levels is  so dramatic over such short
distances that the number  of monitoring sites required would be totally
prohibitive.  Rather, it is  considered appropriate  to monitor a few care-
 fully selected neighborhood  and street canyon sites.  These should be
 selected to typify population exposures under a variety of  conditions, so
 that one can develop from  these a relationship adequate to  project the
 impact in other  similar areas.

2.1.3.4  Photochemical Oxidants/Ozone - The  typical configuration used
 for oxidant or ozone monitoring has been too often only one site in the
urban center of  an AQCR, and frequently the precursor pollutants are mon-
itored at the same site.   Because oxidant, as a secondary pollutant,  is
not closely related  to any geographic source pattern, oxidant levels have
been presumed to be relatively uniform over  large areas, and one downtown
                               11-15

-------
sampling site was not considered too grossly inadequate.  This is not neces-
necessarily the wisest practice, however, due to the scavenging effect of
freshly generated NO from mobile sources.  Figure II-3 presents the typical
diurnal afctern experienced at such a combined site.  The maximum oxidant
levels are not coincident in time with the peak levels of the precursors
and hence are not likely to be coincident in space either.  This leads to
the recommendation that peak sites be located 15 to 25 km from the center
of the city in at least two general directions.  These two general areas
should be selected based on wind directions during the ozone season.  This
season varies, according to local climatology, from May to September in the
North to April to October in the South.  Generally, ozone levels above the
NAAQS are not found when daytime ambient temperatures are below 15°C (60°F).
Consideration may well be given to reduced operation of isolated 03 monitors
during the winter months.

In addition to these peak sites, several neighborhood sites may be necessary
for monitoring population exposures in residential, commercial, and downtown
areas, depending on the population and size of the Region.  For purposes of
determining possible transport of ozone into the region, it may be necessary
to have sites in remote areas upwind.

2.1.3.5  Nitrogen Dioxide - Nitrogen dioxide has a dual role in air pollu-
tion, so that two different sets of network needs must be considered.  There
is an NAAQS for N02, so that peak and neighborhood population exposure must
be monitored.  Because of the lag time indicated in Figure II-3, the peak
N02 exposure will not necessarily be at major traffic points of high NO
emissions.   However, the timing of the peak can vary significantly through
the year (Figure II-4), so that it does not provide a very rigorous
guide for placing sites.  In general, in areas where levels exceed the
standards,  a population-oriented network involving both bubbler and con-
tinuous monitoring should be done in peak areas, while the intermittent
monitoring should be at neighborhood and background sites.  The peak sites
should be located similar to the peak ozone sites, except that they should
be only 10 to 15 km from the center city.
                           11-16

-------
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2.1.3.6  Nonmethane Hydrocarbons and Nitric Oxide - The existing monitoring
of nonmethane hydrocarbon and nitric oxide is  typically a very  limited
effort with one or a few continuous sites in an area.  Since there are no
NAAQS, population-oriented monitoring is not necessary and in most areas
is not conducted.

However, data on both NO and nonmethane hydrocarbons are required along
with N0» and oxidant data to provide research  and planning information with
respect to photochemical oxidant reduction.  Single sites at the  urban
center are clearly not adequate for this purpose, as they do not permit any
resolution of spatial distribution and transport-reaction time  questions.
It is recommended (although not required) that hydrocarbon and  paired NO
                                                                        X
sensors be located in the CBD of the urban core area when reliable instru-
ments for measuring non-methane hydrocarbons become available.
2.1.3.7  Meteorological Sensors - In addition to data on pollutant concen-
trations, it is necessary to have available some source of meteorological
data for use in dispersion modeling and other data analysis efforts utiliz-
ing the monitoring network data.  Hie data should include wind speed, wind
direction, and vertical stability information, although most networks
include only wind speed and direction, since vertical temperature param-
eters are difficult to monitor in urban areas.

Wind data may often be adequately supplied by the National Weather Service
or by commercial consultants.  In other cases, however, the National
Weather Service airport site may be too remote, or the data otherwise less
than adequate, and wind speed and direction sensors should be included in
the air quality monitoring network.  Such sensors, if included, should be
placed at sites where several continuous instruments are housed together,
in order to obtain the greatest use of the data for modeling and research
purposes.  An adequate number of meteorological sensors would probably be
on the order of one-half or less of the number of such stations.
                                 11-19

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Information on vertical stability can usually be adequately obtained in-
directly by utilizing inferred relationships between wind conditions, time
of day, insolation and vertical stability classes.  Observations of temper-
ature at several heights near the surface are very useful to infer stability
for short-term modeling and air quality forecasting, but extensive measure-
ment of vertical parameters is usually only done on a research basis.

2.1.3.8  Combined Sites - As has been noted above, it has been common prac-
tice to consider the configuration of an entire network covering all pol-
lutants, as a whole rather than on a strict pollutant-by-pollutant basis.
This is, of course, done as a matter of economy, both of cost and manpower,
it generally being more economical to have as many sensors collected at
one site as possible.

It is considered appropriate to combine instruments to a certain extent.
However, it is not appropriate to routinely house all instruments for all
pollutants together as has often been common practice, except for back-
ground sites.

The peak and neighborhood type sites for total suspended particulate and
SOp may very reasonably be combined.  As was noted, it is specifically
recommended that in the case of research and planning sites, hydrocarbon
and oxides of nitrogen sensors be collected together together into sta-
tions, which may also reasonably include hi-vols and 862 sensors.
However, as also noted above, the locations of peak levels of the various
pollutants are in most cases not at the same location within the area.
Most prominent example of this is carbon monoxide.  Although it is obvi-
ously convenient to have all the continuous sensors together, it is
extremely rare to find a site large enough for a full monitoring station
that is also in an appropriate location for peak CO monitoring and,
indeed, sites suitable for CO monitoring are not necessarily suitable for

                                  11-20

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other pollutants, depending on the purpose.   Hence it is not prudent to

presume that CO sensors can be located with the others, although if pos-

sible of course it should be done.


2.1.4  Additional Guidance


Other recent and current EPA contract efforts relevant to the issues of

network design, optimization, and evaluation include:

     Guidelines for Air Quality Maintenance Planning and Analysis,
     Volume 11;  "Air Quality Monitoring and Data Analysis"

          Subject Matter;  This document provides states with
          planning information and guidance for the preparation
          and implementation of a monitoring system which is
          compatible with the goal of air quality maintenance
          and the need for the development of Air Quality Main-
          tenance Plans.
          Status;  The guideline document (also identified as
          EPA-450/4-74-012 and OAQPS #1.2-030) has been completed
          by the GGA Corporation, September 1974.

          EPA Project Officer:  Alan J. Hoffman, MRB, HDAD, OAQPS.

     Collection and Integration of Operational Characteristics of
     Existing Pollutant Monitoring Networks

          Subject Matter;  This study deals with the analysis of
          operational data gathered from five superior air and
          water monitoring networks to identify the most efficient
          and economical methodology by which a monitoring network
          can satisfy its responsibilities and optimize the cost-
          effectiveness of daily operations.  The goal of the pro-
          ject is the development of manuals that would furnish
          the desired techniques for evaluating operations, and to
          provide methodologies by which the efficiency and/or
          cost-effectiveness of all operations could be readily
          considered along with the effects  of alternative actions
          where the evaluation indicates that improvement is needed,
          while remaining within budgetary constraints and meeting
          network objectives.

          Status;   The project is being carried out by URS Research
          Corp.  and is expected to be completed by November 1975.

          EPA Project Officers:  Edward A.  Schuck and
                                 Leslie Dunn,  MSA, NERC-LV

                               11-21

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2.2  INSTRUMENT SITING AND PROBE EXPOSURE

After the general location of a sampling site is selected, based on con-
sideration of the Region-wide configuration, it is necessary to select a
site for the sensor or station, and then within the confines of that
choice to determine the precise location of the inlet probe in the case
of gaseous pollutants.

2.2.1  Site Selection

The selection of a precise site, once a general area has been
selected, is primarily a question of availability, accessibility, secu-
rity, and the potential effect of surrounding structures.  The issues of
accessibility and security are the ongoing concerns of the daily opera-
tion of a network, and there is little additional guidance to be offered.
The issues of ground-level versus rooftop sites might be considered a
site-selection problem, as availability is one of the primary reasons for
seeking rooftop sites; however, the impact of the choice is more in the
nature of a probe placement issue, and it is so considered here.

Sulfur dioxide is considered to be rather well mixed near the ground, at
least at receptors not overly affected by specific point sources.  There-
fore, either ground or roof-top sampling is adequate, and the choice can
be made on the basis of site availability.  However, care must be taken to
ensure that rooftops are 'clean,'  i.e., free from space heating vents,
laboratory hood vents, and the like, that may have S02 emissions.  Once above
the effect of reentrainment from the ground, it is generally considered
that TSP is also fairly well mixed for the next few hundred feet above the
ground.   Hence rooftop sampling has traditionally been recommended in order
to avoid influence of possible reentrainment effect, and rooftops up to
several stories high have been used, particularly at center city sites.  If
the reentrainment is to be considered, however, perhaps as part of the popu-
lation exposure, then a site that  permits ground level (2 to 3 meters)
sampling is required.   If such a site is not attainable, an alternate
arrangement such as a portable sampler should be considered.   This is a
                                11-22

-------
clear instance where the purpose of the monitoring needs to be very
precisely stated to determine the appropriate siting action.

The obvious case where station siting depends on the purpose of the
monitoring is with CO, where a station may be either a street canyon,
neighborhood, corridor, or background station.  In contrast to the case
with SC>2, the horizontal distribution of CO across an urban area consists
of so many alternating areas of peak and valley levels, one at each
street or major traffic center, that one must consider site locations
for CO primarily in probe placement terms, in scale of plus or minus a
meter or two.  Hence a peak station site needs to be essentially adja-
cent to the street in question and needs to permit nose-level sampling,
while a neighborhood site must be located at least 35 meters from the
nearest street.  This setback will limit the influence of the nearest street
to about 1 ppm and make the reading more representative of the general
community in which the monitor is located.  The strong dependence of carbon
monoxide concentration upon distance from the nearest roadway has been
illustrated in a number of studies. '   Generally it was found that the
concentrations experienced by pedestrians exceeded those measured at a
typical air monitoring site, while concentrations at randomly selected
locations throughout the survey grid were less than those at the site.
More specifically, the data in one study indicated that average concentra-
tions determined by the monitor would be reduced to near the urban back-
ground level by moving the monitor approximately 200 feet farther back
                o
from the street.   Figure II-5 indicates how the CO levels at the various
stations in Los Angeles are closely related to the slant distance from
the street, despite presumably different traffic volumes in the various
locales.  It is also known that for peak CO sampling within street canyons,
the side of the street which is opposite the side facing the rooftop-level
winds will experience the higher concentrations (see Figure II-6).  Hence
in any location with a significantly prevailing wind direction, even the
choice of the side of the street becomes a relevant siting question.
                               11-23

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                      11-24

-------
                                                          BACKGROUND
                                                        CO CONCENTRATION
                               PRIMARY     RECEPTOR
                               VORTEX
                                   TRAFFIC
                                    LANE
                               -W-
Figure II-6.   Schematic of cross-street  circulation in street  canyon'
                                 11-25

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2.2.2  Probe Placement

Within the several meters scale involved in a typical monitoring site,
there is general latitude in the precise placement of the inlet probe.
For the gaseous pollutants (excepting CO), this is an issue primarily
involving security from vandalism, the avoidance of any restrictions
to the air flow, such as from the station itself, trees, etc., and any
undue influence from a minor local source, such as a stack located on
the roof of a building where the air inlet is located.  These require-
ments are generally taken to indicate a height above the ground of 3
to 15 meters, and either a vertical clearance above the roof of 1 to
2 meters or, in a different configuration, a horizontal clearance
beyond the supporting structure of at least 2 meters.

In the case of particulates, the hi-vol represents a special situation.
Historically, the NASN hi-vols have been on rooftops, sometimes 8 to
10 stories high.  This avoids reentrained surface dust, and the atten-
dant variability, and in so doing provides a smoother, more reliable
record for trend purposes.  However, it can be argued that elevating
the sampler in this way makes the resulting data an inaccurate reflec-
tion of true population exposure.  Table II-4 provides, as an example,
a comparison of 5 months' data from the CAMP Station in Philadelphia
and the Franklin Institute site operated by the Philadelphia Department
of Public Health.  The CAMP Station hi-vol, at 11 feet, reads consis-
tently higher than the City Station, at the same location, which is at
about 50 feet.  It is probably also true, though perhaps less thoroughly
demonstrated, that the distance of the hi-vol from a nearby street is of
importance.   Since streets, walkways, and other such areas are a source
of reentrained particulate matter, it is probable that placing a hi-vol
on a one-story roof, for instance, is not the same as placing it in an
open area or on a trailer, even if the height above the ground is the
same.
                               11-26

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The pollutants NMHC, NO, N02 and Oo are tied together in a precursor -
secondary product relationship and should therefore be considered as
an integrated system in site selection.  While hydrocarbons are emitted
in much the same pattern as CO, an elevated site in the CBD is more appro-
priate than a ground level one.  This is to limit the influence of any
single street and provide a more representative measurement of the CBD
as a whole.  NO and N0£ should be monitored at this location to provide
information on ratios of NMHC to NO and N02-

As photochemically produced secondary pollutants, N02 and 03 are con-
sidered to be well mixed vertically and of relatively uniform concen-
tration over a large area.  Therefore, either rooftop or ground level
sampling are adequate and the prime concern is the location of a
favorable distance downwind of the CBD to locate the zone of maximum
concentration.  Under normal wind speeds, this zone thought to be 10-
15 km for N0£ and 15-25 km for oxidants.  Special precaution should be
taken not to locate 03 sites within 100 meters of major traffic
arteries or large parking areas due to the scavenging effect of NO
emissions.
                               II-26B

-------
Table II-4.  COMPARISON OF HI-VOL DATA AT TWO DIFFERENT
             HEIGHTS - FRANKLIN INSTITUTE, PHILADELPHIA
Date
Nov. 1, 1974
Nov. 13, 1974
Nov. 19, 1974
Nov. 25, 1974
Dec. 1, 1974
Dec. 7, 1974
Dec. 13, 1974
Dec. 19, 1974
Dec. 25, 1974
Dec. 31, 1974
Jan. 1, 1975
Jan. 6, 1975
Jan. 8, 1975
Jan. 12, 1975
Jan. 18, 1975
Jan. 24, 1975
Jan. 30, 1975
Feb. 5, 1975
Feb. 23, 1975
Mar. 1, 1975
Mar. 7, 1975
Mar. 13, 1975
Mar. 19, 1975
Mar. 25, 1975
Mar. 31, 1975
Geometric mean
City
199
48
122
69
73
113
174
94
101
54
31
88
107
42
54
153
44
45
64
80
119
84
56
84
46
76
CAMP
264
76
187
116
117
154
237
133
143
82
52
190
136
71
76
228
81
76
138
254
206
122
92
128
94
125
Ratio
1.33
1.58
1.53
1.68
1.60
1.36
1.36
1.41
1.42
1.52
1.68
2.16
1.27
1.69
1.41
1.49
1.84
1.69-
2.16
3.18
1.73
1.45
1.64
1.52
2.15
1.64
                         11-27

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It is recognized that the effect of height seen in Table 2, and other
similar concerns, indicate that many of the hi-vol networks and sam-
pling sites that have been used in the past are generally not as com-
parable with each other as is the case with other pollutants.  Ulti-
mately, the need for a greater degree of homogeneity will likely require
that adjustments be made in the way hi-vols are typically placed.  How-
ever, because of the large number of sites involved, and the length of
historical record at many of them, such an adjustment would be an issue
of major concern and significance.  Since a large amount of good quanti-
tative information on the topic is not currently available, it is con-
sidered inappropriate to make major recommendations at the present.  The
effect of height, etc., can be taken into consideration in interpreting
hi-vol data, and it is recommended that this be consistently done.
Several study programs are underway that will provide much better infor-
mation on these questions in the near future, and the guidance material
will then be revised as appropriate.  It is expected that guidance in this
area will be in the form of a supplement to this document, similar to the
CO Supplement, and will be issued in early 1976.

However, the issue of probe placement is the most serious concern in the
case of CO.  Even within the scale of a typical monitoring site, CO
levels can vary dramatically.  As indicated in Figure II-7, CO levels
can change with vertical height at a rate more than 1/2 ppm per meter.
Figure II-8 illustrates the sizable changes possible with short hori-
zontal changes in the vicinity of a typical peak site location.  Thus,
while there is no single "right" position for a CO probe, it is obious
that some major degree of standardization is needed to ensure uniformity.
The currently recommended positions are discussed in Supplement A.  These
positions were selected not only to standardize probe and station
locations, but also to provide a reasonable measure of population exposure
in the breathing zone.

A summary of the current recommendations concerning station siting and
probe placement is presented Table II-5.
                                   11-28

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                    40
                     30
                    20
                 UJ
                 X
                     10
                                                   LEEWARD SIDE
                                                   OF STREET
        WINDWARD SIDE
        OF STREET
                         i  I   I  I   I  I  I  I   I  V  i  i  i   i  I
                       0
10          15

   CO,ppm
20
s
              Figure  II-7.  The vertical distribution of CO concentration on a

                           street with traffic volume of 1,500 vehicles/hour''
                                          11-29

-------
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11-30

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2.2.3  Additional Guidance


Other recent and current EPA contract studies relevant to the issues

of site selection and probe placement include:

     "Selecting Sites for Carbon Monoxide Monitoring"

          Subject Matter;  This report presents procedures and
          criteria for selecting appropriate locations for CO
          monitoring stations which fulfill specific monitoring
          objectives.  Procedures are given for selecting loca-
          tions that will provide CO measurements representative
          of downtown street canyon areas, urban neighborhoods,
          and larger interurban regions.   Specific recommenda-
          tions are given for inlet heights, distance from major
          and minor roadways and placement re ative to urban
          areas.  Ihe rationale behind each specific recommenda-
          tion is also given.

          Status;  The first draft report prepared for EPA by
          Stanford Research Institute is  being reviewed.   A
          final report is expected by the end of September 1975

          EPA Project Officer;  Neil J.  Berg, Jr., MRB, MDAD, OAQPS
                              11-31

-------
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8

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"Determine Optimum Site Exposure Criteria for TSP Monitoring"

     Subject Matter;  The purpose of this contract is to develop
     specific optimum site exposure criteria for TSP monitoring
     which could be applied generally.  Criteria will be developed
     for a limited number of different types of sites, each of
     which achieves some specific monitoring objective or set of
     objectives.  This will be accomplished by the following:
     (1) conduct a literature search on the nature and purpose
     of ambient TSP monitoring; (2) determine a specific set of
     objectives to be achieved by ambient TSP monitoring and the
     relative importance of each objective; (3) delineate repre-
     sentative types of monitoring sites which achieve one or
     more of the monitoring objectives; (4) for each representa-
     tive type of site, determine optimum exposure criteria which
     could be applied uniformly to that type of site; and (5) for
     each type of site, determine the relative effects of various
     TSP sources both nearby emitters and those further away.

     Status;  Stanford Research Institute has been chosen to
     perform this study.

     The expected completion date is March 1, 1976.

     EPA Project Officer;  Neil J. Berg, Jr., MRB, MDAD, OAQPS.

"Determine Optimum Site Exposure Criteria for SO^ Monitoring"

     Subject Matter:  This project is similar to the one for TSP
     monitoring described above.

     Status:   The Center for Environment and Man has been chosen

     to perform this study.   Estimated completion date is February 1,  1976.

     EPA Project Officer;  Neil J. Berg, Jr., MRB, MDAD, OAQPS.
     Monitoring and Data Analysis Division.

"Study of the Feasibility of Determining Optimum Site Exposure
Criteria for 0,_, NO,,, and Hydrocarbon Monitoring"
              y~-   L

     Subject Matter:  The purpose of this contract is to in-
     vestigate the feasibility of determining optimum site
     exposure criteria for Ox, N02 and hydrocarbon monitoring
     which could be applied generally.  This will be accom-
     plished by the following:  (1) conduct a literature search
     on the nature and purposes of Ox, N02 and HC monitoring;
     (2) determine a specific set of objectives to be achieved
     by Ox, N02 and HC monitoring, and the relative importance
                          11-34

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          of each (if there is a lack of data which precludes this
          determination of monitoring objectives, fully document
          this data void and suggest means to obtain the necessary
          information); (3) delineate representative types of moni-
          toring sites which achieve one or more of the monitoring
          objectives; and (4) prepare a final report summarizing as-
          sumptions, findings, and conclusions of this study.

          Status;  Stanford Research Institute has been chosen to
          perform this study.  Estimated completion date is December 1,

          1975.
          EPA Project Officer;  Neil J. Berg, Jr., MRB, MDAD, OAQPS

     "Development of a Study Plan to Determine the Air Quality Grad-
     ients at Air Monitoring Sites"

          Subject Matter;   The purpose of this contract is to develop
          a study plan to define the area for which a point samplers
          data may be "representative."  The study plan should address
          various pollutants, differing monitoring objectives, and
          site exposure criteria in determining the three-dimensional
          air quality gradients around monitoring sites.   The plan
          should define limits of "representativeness" as well.

          Status:   Rockwell  International  Air Monitoring  Center has

          been chosen to perform this study.   The expected completion

          date is December 1, 1975

          EPA Project Officer;  Alan J. Hoffman,  MRB, MDAD, OAQPS


2.3  NETWORK OPERATION


In addition to defining the configuration of the  network and actually
siting the monitors, the process of monitoring network design also in-
cludes the selection of appropriate instrumentation and the definition
of various procedures for the operation of the network.


2.3.1  Monitoring Equipment Selection


The selection of monitoring instruments for use in a network is an im-

portant aspect of overall network planning.   EPA  has established a set

of procedures for establishing whether monitoring methods are reference

                                11-35

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methods or equivalents, and thus acceptable for meeting SIP requirements.
This was published as a regulation in 40 CFR 53 on February 18, 1975.
The burden of proof of whether an analyzer is a reference method or
equivalent falls upon the manufacturer.  Many analyzers currently in
use are no longer manufactured per se (that is the specific make and
model).  Since the vendor will have no incentive to test these analyzers
for reference method or equivalency, EPA will in most cases make the
necessary tests.

2.3.1.1  Reference Method Determination - For S0? and TSP, the measure-
ment principle specified is a manual method.  (Pararosaniline for SCL,
hi-vol for TSP) thus, there is only one reference method for S02 and TSP
since the method consists of a series of mechanical steps or chemical
operations to be performed.  For CO, ozone and N0«, only the measurement
principle and calibration procedure has been specified.  Any analyzer
utilizing the specified measurement principle and calibration procedure
and which meets the performance specifications in 40 CFR 53 will be
designated as a reference method.  Thus, as an example, there could be
as many reference methods for CO as there are different models  of
NDIR analyzers.

2.3.1.2  Equivalency Determination - In general, equivalency to a refer-
ence method is determined by passing the tests for demonstrating a
consistent relationship to a reference method and by meeting performance
specifications.  If the candidate equivalent method is a manual method
only the consistent relationship need by established.  If the method is
an automated method then both the consistent relationship and performance
specification tests must be passed in order to be designated as an
equivalent method.

At the present time, reference methods exist only for SO  and TSP which
are described in 40 CFR 50.  They are the high volume procedure for TSP
and the pararosaniline (sulfamic acid) procedure for S0~.  Any other
manual methods for these pollutants are unacceptable.

                               11-36

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For CO and ozone, EPA is awaiting data from manufacturers before designat-
ing any reference methods.  For the present time, any instrument utiliz-
ing the NDIR measurement principle for CO and the chemiluminescent prin-
ciple for ozone will be acceptable.  It is possible that instruments
utilizing the NDIR principle for CO or the chemiluminescent for 0,. will
be unacceptable.  This situation could occur if the manufacturer fails
(or if EPA tests the analyzer and it fails) to pass the performance
specifications tests.

For NO-, no reference measurement principle or methods exists since the
Jacobs-Hochheiser (J-H) technique was rescinded.  The chemiluminescent
measurement principle will be proposed very soon to replace the J-H tech-
nique.  The triethanolamine guiacol sulfite orifice method (TGS) and the
sodium arsenite orifice (ARS) method will be tested for equivalency as
soon as a reference method is designated.

Unacceptable manual methods should be changed to the reference method
or equivalent within 6 months.  Unacceptable analyzers (automated methods)
should be changed to a reference method or equivalent as soon as prac-
ticable but no later than 5-years (February 1980).

Automated analyzers not utilizing the reference measurement principle
and calibration procedure and which fail equivalency tests should be
replaced with a reference method as soon as practicable but no later
than 5-years (February 1980).

2.3.2  Operating Procedures

There are at least two types of operational decisions that affect the
design of the network in the sense that they affect the type of data
produced.  In the case of intermittent sampling, the frequency of opera-
tion is such a decision, and in the case of continuous monitoring, the
selection of the instrument operation range is also.  Note that the many
                                11-37

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other operating procedures associated with the quality assurance aspects
of a monitoring network are not considered here, although they are none-
theless of major importance also.

2.3.2.1  Intermittent Sampling Frequency - The entire point of sampling
intermittently, such as the every-6-days schedule used for hi-vols and
bubblers, is to provide some measure of air quality knowledge at a cost
less than that associated with more frequent sampling.  Such a program
necessarily introduces some uncertainty into the statements that can be
made based on the resulting data.  However, standard statistical pro-
cedures are available to provide estimates of this uncertainty, and to
indicate how to adjust the sampling frequency to provide an appropriate
degree of uncertainty.

Figure II-9 indicates how the range of uncertainty with respect to the
NAAQS varies with the sampling frequency.  At 61 samples per year, an
                                         3
annual mean TSP level of 75 may be 8 ug/m  higher or lower (95 percent
confidence limits); if the sampling frequency is tripled, the uncer-
                        3
tainty drops to + 3 (ig/m .  Thus, with sites having levels near the
standard, greater sampling frequency may be needed to precisely define
compliance, while at sites with levels well above or well below the
standard, less frequent sampling may be adequate.  It should also be
noted that the uncertainty increases or decreases linearly with the
value of the standard geometric deviation; the 1.6 used to calculate
Figure II-9 is a typical value.

Table II-6 presents similar information relevant to the 24-hour standards;
specifically the table presents the probability, for each of three sam-
pling frequencies,  that at least 2 of the days over the 24-hour standard
will be detected; i.e., that the site will be considered in violation of
the standard.  Note that, again, if the site is only marginally in viola-
tion, quite frequent sampling is needed to detect this, while a site a
large number of excursions is almost assured of being so identified„
                               11-38

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                 11-39

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  Table II-6.  PROBABILITY OF SELECTING TWO OR MORE DAYS WHEN SITE
               EXCEEDS STANDARD
Actual number of
excursions
2
4
6
8
10
12
14
16
18
20
22
24
26
Sampling frequency, days/year
61/365
0.03
0.13
0.26
0.40
0.52
0.62
0.71
0.78
0.83
0.87
0.91
0.93
0.95
122/365
0.11
0.41
0.65
0.81
0.90
0.95
0.97
0.98
0.99
0.99
0.99
0.99
0.99
183/365
0.25
0.69
0.89
0.96
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
2.3.2.2  Instrument Operating Range - Since continuous instruments can
usually be adjusted electronically to operate in various concentration
ranges, the selection of such range is a necessary decision in the pro-
cess of network design.  Generally, the decision is simply to utilize
the smallest range that will encompass the maximum expectable levels,
and this is usually adequate.  However, in the case where very high
levels (usually S09) from a major source are received at a site that
normally experiences low background levels, the use of a single range may
not be possible.  If the range is set too low, accurate documentation of
the peaks is lost offscale, while if it is chosen high, there will not be
adequate precision in the data concerning the low levels.  There is no
way to resolve this with a single instrument.  In such a case, one or the
other orientation (population or source)  must be selected as primary, and
the instrument site coded 01 or 02 as appropriate.   A good solution would
                                11-40

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be to have a continuous instrument adjusted to measure the peak levels,
and a bubbler for long term population exposure.
                               11-41

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                               SECTION III

                               REFERENCES


1.  Code of Federal Regulations.  Title 40.  Section 51.17.

2.  Federal Register.  Volume 33, Number 10.  January 16, 1968.

3.  McCormick, Robert A.  Air Pollution Climatology.  Chapter 9 in
    Stern A.C., Air Pollution.  2nd Edition.  Academic Press.  1968.

4.  Lynn, David A.  Air Pollution-Threat and Response (in press)
    Addison-Wesley.  Reading, Mass.  1976.

5.  CAMP in Washington, B.C. 1962-1963.  Publication Number AP-23.
    Department of Health, Education and Welfare.  1966.

6.  Kinosian, John R. and Dean Simeroth.  The Distribution of Carbon
    Monoxide and Oxidant Concentrations in Urban Areas.  California
    Air Resources Board.  1973.

7.  Johnson, W. B. et al.  Field Study for Initial Evaluation of
    an Urban Diffusion Model for Carbon Monoxide (APRAC-la).  Contract
    CAPA-3-68 (1-69).  Stanford Research Institute.  1971.

8.  Ott, Wayne R.  An Urban Survey Technique for Measuring the Spatial
    Variation of Carbon Monoxide Concentrations in Cities.  Depart-
    ment of Civil Engineering.  Stanford University.  1971.

9.  Guidelines for the Interpretation of Air Quality Standards.  OAQPS
    Guideline Numbers 1.2 - 008.  1974.
                              III-l

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