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2.8.1.7.3 A Monitoring Planning Area may have one or more community monitoring zones (CMZ) for aggregation of data from eligible SLAMS and SPM sites for comparison to the annual NAAQS. The planning area has large gradients of average air quality and, as shown in Figure 2 may be assigned three CMZs: An industrial zone, a downtown central business district (CBD), and a residential area. (If there is not a large difference between downtown concentrations and other residential areas, a separate CBD zone would not be appropriate).
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2.8.1.7.4 Figure 3 of this appendix illustrates how CMZs and PM2.5 monitors might be located in a hypothetical MPA typical of a Western State. Western States with more localized sources of PM and larger geographic area could require a different mix of SLAMS and SPM monitors and may need more total monitors. As the networks are deployed, the available monitors may not be sufficient to completely represent all geographic portions of the Monitoring Planning Area. Due to the distribution of pollution and population and because of the number and spatial representativeness of monitors, the MPAs and CMZs may not cover the entire State.
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2.8.1.7.5 Figure 4 of this appendix shows how the MPAs, CMZs, and PM2.5 monitors might be distributed within a hypothetical State. Areas of the State included within MPAs are shown within heavy solid lines. Two MPAs are illustrated. Areas in the State outside the MPAs will also include monitors, but this monitoring coverage may be limited. This portion of the State may also be represented by CMZs (shown by areas enclosed within dotted lines). The monitors that are intended for comparison to the NAAQS are indicated by X. Furthermore, eligible monitors within a CMZ could be averaged for comparison to the annual NAAQS or examined individually for comparison to both NAAQS. Both within the MPAs and in the remainder of the State, some special study monitors might not satisfy applicable 40 CFR part 58 requirements and will not be eligible for comparison to the NAAQS.
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2.8.2 Substitute PM Monitoring Sites.
2.8.2.1 Section 2.2 of appendix C of this part describes conditions under which TSP samplers can be used as substitutes for PM10. This provision is intended to be used when PM10 concentrations are expected to be very low and substitute TSP samplers can be used to satisfy the minimum number of PM10 samplers needed for an adequate PM10 network.
2.8.2.2 If data produced by substitute PM samplers exceed the concentration levels described in appendix C of this part, then the need for this sampler to be converted to a PM10 or PM2.5 sampler, shall be considered in the PM monitoring network review. If the State does not believe that a PM10 or PM2.5 sampler should be sited, the State shall submit documentation to EPA as part of its annual PM report to justify this decision. If a PM site is not designated as a substitute site in the PM monitoring network description, then high concentrations at this site would not necessarily cause this site to become a PM2.5 or PM10 site, whichever is indicated.
2.8.2.3 Consistent with §58.1, combinations of SLAMS PM10 or PM2.5 monitors and other monitors may occupy the same structure without any mutual effect on the regulatory definition of the monitors.
3. Network Design for National Air Monitoring Stations (NAMS)
The NAMS must be stations selected from the SLAMS network with emphasis given to urban and multisource areas. Areas to be monitored must be selected based on urbanized population and pollutant concentration levels. Generally, a larger number of NAMS are needed in more polluted urban and multisource areas. The network design criteria discussed below reflect these concepts. However, it should be emphasized that deviations from the NAMS network design criteria may be necessary in a few cases. Thus, these design criteria are not a set of rigid rules but rather a guide for achieving a proper distribution of monitoring sites on a national scale.
The primary objective for NAMS is to monitor in the areas where the pollutant concentration and the population exposure are expected to be the highest consistent with the averaging time of the NAAQS. Accordingly, the NAMS fall into two categories:
Category (a): Stations located in area(s) of expected maximum concentrations, generally microscale for CO, microscale or middle scale for Pb, middle scale or neighborhood scale for population-oriented particulate matter, urban or regional scale for Regional transport PM2.5, neighborhood scale for SO2, and NO2, and urban scale for O3.
Category (b): Stations which combine poor air quality with a high population density but not necessarily located in an area of expected maximum concentrations (neighborhood scale, except urban scale for NO2). Category (b) monitors would generally be representative of larger spatial scales than category (a) monitors.
For each urban area where NAMS are required, both categories of monitoring stations must be established. In the case of Pb and SO2 if only one NAMS is needed, then category (a) must be used. The analysis and interpretation of data from NAMS should consider the distinction between these types of stations as appropriate.
For each MSA where NAMS are required, both categories of monitoring stations must be established. In the case of SO2 if only one NAMS is needed, then category (a) must be used. The analysis and interpretation of data from NAMS should consider the distinction between these types of stations as appropriate.
The concept of NAMS is designed to provide data for national policy analyses/trends and for reporting to the public on major metropolitan areas. It is not the intent to monitor in every area where the NAAQS are violated. On the other hand, the data from SLAMS should be used primarily for nonattainment decisions/ analyses in specific geographical areas. Since the NAMS are stations from the SLAMS network, station locating procedures for NAMS are part of the SLAMS network design process.
3.1 [Reserved]
3.2 Sulfur Dioxide (SO2) Design Criteria for NAMS. It is desirable to have a greater number of NAMS in the more polluted and densely populated urban and multisource areas. The data in table 3 show the approximate number of permanent stations needed in urban areas to characterize the national and regional SO2 air quality trends and geographical patterns. These criteria require that the number of NAMS in areas where urban populations exceed 1,000,000 and concentrations also exceed the primary NAAQS may range from 6 to 10 and that in areas where the SO2 problem is minor, only one or two (or no) monitors are required. For those cases where more than one station is required for an urban area, there should be at least one station for category (a) and category (b) objectives as discussed in section 3. Where three or more stations are required, the mix of category (a) and (b) stations is determined on a case-by-case basis. The actual number and location of the NAMS must be determined by EPA Regional Offices and the State Agency, subject to the approval of EPA Headquarters, Office of Air Quality Planning and Standards (OAQPS).
Table 3_SO2 National Air Monitoring Station Criteria
[Approximate number of stations per area] a
------------------------------------------------------------------------
High Medium Low
Population category concentration concentration concentration
b c d
------------------------------------------------------------------------
>1,000,000 6-10 4-8 2-4
500,000 to 1,000,000 4-8 2-4 1-2
250,000 to 500,000 3-4 1-2 0-1
100,000 to 250,000 1-2 0-1 0
------------------------------------------------------------------------
a Selection of urban areas and actual number of stations per area will
be jointly determined by EPA and the State agency.
b High concentration_exceeding level of the primary NAAQS.
c Medium concentration_exceeding 60 percent of the level of the primary
or 100% of the secondary NAAQS.
d Low concentration_less than 60 percent of the level of the primary or
100% of the secondary NAAQS.
The estimated number of SO2 NAMS which would be required nationwide ranges from approximately 200 to 300. This number of NAMS SO2 monitors is sufficient for national trend purposes due to the low background SO2 levels, and the fact that air quality is very sensitive to SO2 emission changes. The actual number of stations in any specific area depends on local factors such as meteorology, topography, urban and regional air quality gradients, and the potential for significant air quality improvements or degradation. The greatest density of stations should be where urban populations are large and where pollution levels are high. Fewer NAMS are necessary in the western States since concentrations are seldom above the NAAQS in their urban areas. Exceptions to this are in the areas where an expected shortage of clean fuels indicates that ambient air quality may be degraded by increased SO2 emissions. In such cases, a minimum number of NAMS is required to provide EPA with a proper national perspective on significant changes in air quality.
Like TSP, the worst air quality in an urban area is to be used as the basis for determining the required number of SO2 NAMS (see table 3). This includes SO2 air quality levels within populated parts of urbanized areas, that are affected by one or two point sources of SO2 if the impact of the source(s) extends over a reasonably broad geographic scale (neighborhood or larger). Maximum SO2 air quality levels in remote unpopulated areas should be excluded as a basis for selecting NAMS regardless of the sources affecting the concentration levels. Such remote areas are more appropriately monitored by SLAMS or SPM networks and/or characterized by diffusion model calculations as necessary.
3.3 Carbon Monoxide (CO) Design Criteria for NAMS. Information is needed on ambient CO levels in major urbanized areas where CO levels have been shown or inferred to be a significant concern. At the national level, EPA will not routinely require data from as many stations as are required for PM–10, and perhaps SO2, since CO trend stations are principally needed to assess the overall air quality progress resulting from the emission controls required by the Federal motor vehicle control program (FMVCP) and other local controls.
Although State and local air programs may require extensive monitoring to document and measure the local impacts of CO emissions and emission controls, an adequate national perspective is possible with as few as two stations per major urban area. The two categories for which CO NAMS would be required are: (a) Peak concentration areas such as are found around major traffic arteries and near heavily traveled streets in downtown areas (micro scale); and (b) neighborhoods where concentration exposures are significant (middle scale, neighborhood scale).
The peak concentration station (micro scale) is usually found near heavily traveled downtown streets (street canyons), but could be found along major arterials (corridors), either near intersections or at low elevations which are influenced by downslope drainage patterns under low inversion conditions. The peak concentration station should be located so that it is representative of several similar source configurations in the urban area, where the general population has access. Thus, it should reflect one of many potential peak situations which occur throughout the urban area. It is recognized that this does not measure air quality which represents large geographical areas. Thus, a second type of station on the neighborhood scale is necessary to provide data representative of the high concentration levels which exist over large geographical areas.
The category (b) (middle scale or neighborhood scale) should be located in areas with a stable, high population density, projected continuity of neighborhood character, and high traffic density. The stations should be located where no major zoning changes, new highways, or new shopping centers are being considered. The station should be where a significant CO pollution problem exists, but not be unduly influenced by any one line source. Rather, it should be more representative of the overall effect of the sources in a significant portion of the urban area.
Because CO is generally associated with heavy traffic and population clusters, an urbanized area with a population greater than 500,000 is the principal criterion for identifying the urban areas for which pairs of NAMS for this pollutant will be required. The criterion is based on judgment that stations in urban areas with greater than 500,000 population would provide sufficient data for national analysis and national reporting to Congress and the public. Also, it has generally been shown that major CO problems are found in areas greater than 500,000 population.
3.4 Ozone (O3) Design Criteria for NAMS. The criterion for selecting locations for ozone NAMS is any urbanized area having a population of more than 200,000. This population cut off is used since the sources of hydrocarbons are both mobile and stationary and are more diverse. Also, because of local and national control strategies and the complex chemical process of ozone formation and transport, more sampling stations than for CO are needed on a national scale to better understand the ozone problem. This selection criterion is based entirely on population and will include those relatively highly populated areas where most of the oxidant precursors originate.
Each urban area will generally require only two ozone NAMS, One station would be representative of maximum ozone concentrations (category (a), urban scale) under the wind transport conditions as discussed in section 2.5. The exact location should balance local factors affecting transport and buildup of peak O3 levels with the need to represent population exposure. The second station (category (b), neighborhood scale), should be representative of high density population areas on the fringes of the central business district along the predominant summer/fall daytime wind direction. This latter station should measure peak O3 levels under light and variable or stagnant wind conditions. Two ozone NAMS stations will be sufficient in most urban areas since spatial gradients for ozone generally are not as sharp as for other criteria pollutants.
3.5 Nitrogen Dioxide (NO2) Criteria for NAMS. Nitrogen dioxide NAMS will be required in those areas of the country which have a population greater than 1,000,000. These areas will have two NO2 NAMS. It is felt that stations in these major metropolitan areas would provide sufficient data for a national analysis of the data, and also because NO2 problems occur in areas of greater than 1,000,000 population.
Within urban areas requiring NAMS, two permanent monitors are sufficient. The first station (category (a), middle scale or neighborhood scale) would be to measure the photochemical production of NO2 and would best be located in that part of the urban area where the emission density of NOX is the highest. The second station (category (b) urban scale), would be to measure the NO2 produced from the reaction of NO with O3 and should be downwind of the area of peak NOX emission areas.
3.6 Lead (Pb) Design Criteria for NAMS. In order to achieve the national monitoring objective, one NAMS site must be located in one of the two cities with the greatest population in the following ten regions of the country (the choice of which of the two metropolitan areas should have the lead NAMS requirement is made by the Administrator or the Administrator's designee using the recommendation of the Regional Administrators or the Regional Administrators' designee):
Table 1_EPA Regions & Two Current Largest MSA/CMSAs (Using 1995
Census Data)
------------------------------------------------------------------------
Region (States) Two Largest MSA/CMSAs
------------------------------------------------------------------------
I (Connecticut, Massachusetts, Maine, Boston-Worcester-Lawrence CMSA,
New Hampshire, Rhode Island, Vermont). Hartford, CT MSA.
II (New Jersey, New York, Puerto Rico, New York-Northern New Jersey-
U.S. Virgin Islands). Long Island, CMSA, San Juan-
Caguas-Arecibo, PR CMSA.
III (Delaware, Maryland, Pennsylvania, Washington-Baltimore CMSA,
Virginia, West Virginia, Washington, Philadelphia-Wilmington-
DC). Atlantic City CMSA.
IV (Alabama, Florida, Georgia, Miami-Fort Lauderdale CMSA,
Kentucky, Mississippi, North Carolina, Atlanta, GA MSA.
South Carolina, Tennessee).
V (Illinois, Indiana, Michigan, Chicago-Gary-Kenosha CMSA,
Minnesota, Ohio, Wisconsin). Detroit-Ann Arbor-Flint CMSA.
VI (Arkansas, Louisiana, New Mexico, Dallas-Fort Worth CMSA, Houston-
Oklahoma, Texas). Galveston-Brazoria CMSA.
VII (Iowa, Kansas, Missouri, Nebraska). St. Louis MSA, Kansas City MSA.
VIII (Colorado, Montana, North Dakota, Denver-Boulder-Greeley CMSA,
South Dakota, Utah, Wyoming). Salt Lake City-Ogden MSA.
IX (American Samoa, Arizona, Los Angeles-Riverside-Orange
California, Guam, Hawaii, Nevada). County CMSA, San Francisco-
Oakland-San Jose CMSA.
X (Alaska, Idaho, Oregon, Washington).. Seattle-Tacoma-Bremerton CMSA,
Portland-Salem CMSA.
------------------------------------------------------------------------
In addition, one NAMS site must be located in each of the MSA/CMSAs where one or more violations of the quarterly Pb NAAQS have been recorded over the previous eight quarters. If a violation of the quarterly Pb NAAQS is measured at a monitoring site outside of a MSA/CMSA, one NAMS site must be located within the county in a populated area, apart from the Pb source, to assess area wide Pb air pollution levels. These NAMS sites should represent the maximum Pb concentrations measured within the MSA/CMSA, city, or county that is not directly affected from a single Pb point source. Further, in order that on-road mobile source emissions may continue to be verified as not contributing to lead NAAQS violations, roadside ambient lead monitors should be considered as viable NAMS site candidates. A NAMS site may be a microscale or middle scale category (a) station, located adjacent to a major roadway (e.g., >30,000 ADT), or a neighborhood scale category (b) station that is located in a highly populated residential section of the MSA/CMSA or county where the traffic density is high. Data from these sites will be used to assess general conditions for large MSA/CMSAs and other populated areas as a marker for national trends, and to confirm continued attainment of the Pb NAAQS. In some cases, the MSA/CMSA subject to the latter lead NAMS requirement due to a violating point source will be the same MSA/CMSA subject to the lead NAMS requirement based upon its population. For these situations, the total minimum number of required lead NAMS is one.
3.7 Particulate Matter Design Criteria for NAMS.
3.7.1 Table 4 indicates the approximate number of permanent stations required in MSAs to characterize national and regional PM10 air quality trends and geographical patterns. The number of PM10 stations in areas where MSA populations exceed 1,000,000 must be in the range from 2 to 10 stations, while in low population urban areas, no more than two stations are required. A range of monitoring stations is specified in table 4 because sources of pollutants and local control efforts can vary from one part of the country to another and therefore, some flexibility is allowed in selecting the actual number of stations in any one locale.
3.7.2 Through promulgation of the NAAQS for PM2.5, the number of PM10 SLAMS is expected to decrease, but requirements to maintain PM10 NAMS remain in effect. The PM10 NAMS are retained to provide trends data, to support national assessments and decisions, and in some cases to continue demonstration that a NAAQS for PM10 is maintained as a requirement under a State Implementation Plan.
3.7.3 The PM2.5 NAMS shall be a subset of the core PM2.5 SLAMS and other SLAMS intended to monitor for regional transport. The PM2.5 NAMS are planned as long-term monitoring stations concentrated in metropolitan areas. A target range of 200 to 300 stations shall be designated nationwide. The largest metropolitan areas (those with a population greater than approximately one million) shall have at least one PM2.5 NAMS stations.
3.7.4 The number of total PM2.5 NAMS per Region will be based on recommendations of the EPA Regional Offices, in concert with their State and local agencies, in accordance with the network design goals described in sections 3.7.5 through 3.7.7 of this appendix. The selected stations should represent the range of conditions occurring in the Regions and will consider factors such as total number or type of sources, ambient concentrations of particulate matter, and regional transport.
3.7.5 The approach for PM2.5 NAMS is intended to give State and local agencies maximum flexibility while apportioning a limited national network. By advancing a range of monitors per Region, EPA intends to balance the national network with respect to geographic area and population. Table 5 presents the target number of PM2.5 NAMS per Region to meet the national goal of 200 to 300 stations. These numbers consider a variety of factors such as Regional differences in metropolitan population, population density, land area, sources of particulate emissions, and the numbers of PM10 NAMS.
3.7.6 States will be required to establish approximately 50 NAMS sites for routine chemical speciation of PM2.5. These sites will include those collocated at approximately 25 PAMS sites and approximately 25 other core SLAMS sites to be selected by the Administrator. After 5 years of data collection, the Administrator may exempt some sites from collecting speciated data. The number of NAMS sites at which speciation will be performed each year and the number of samples per year will be determined by the Administrator.
3.7.7 Since emissions associated with the operation of motor vehicles contribute to urban area particulate matter levels, consideration of the impact of these sources must be included in the design of the NAMS network, particularly in MSAs greater than 500,000 population. In certain urban areas particulate emissions from motor vehicle diesel exhaust currently is or is expected to be a significant source of particulate matter ambient levels. The actual number of NAMS and their locations must be determined by EPA Regional Offices and the State agencies, subject to the approval of the Administrator as required by §58.32. The Administrator's approval is necessary to ensure that individual stations conform to the NAMS selection criteria and that the network as a whole is sufficient in terms of number and location for purposes of national analyses.
Table 4_PM10 National Air Monitoring Station Criteria
[Approximate Number of Stations per MSA] \1\
----------------------------------------------------------------------------------------------------------------
High Medium Low
Population Category Concentration Concentration Concentration
\2\ \3\ \4\
----------------------------------------------------------------------------------------------------------------
>1,000,000...................................................... 6-10 4-8 2-4
500,000-1,000,000.................................................. 4-8 2-4 1-2
250,000-500,000.................................................... 3-4 1-2 0-1
100,000-250,000.................................................... 1-2 0-1 0
----------------------------------------------------------------------------------------------------------------
1 Selection of urban areas and actual number of stations per area will be jointly determined by EPA and the
State agency.
2 High concentration areas are those for which ambient PM10 data show ambient concentrations exceeding either
PM10 NAAQS by 20 percent or more.
3 Medium concentration areas are those for which ambient PM10 data show ambient concentrations exceeding 80
percent of the PM10 NAAQS.
4 Low concentration areas are those for which ambient PM10 data show ambient concentrations less than 80 percent
of the PM10 NAAQS.
3.7.7.1 Selection of urban areas and actual number of stations per area will be jointly determined by EPA and the State agency.
3.7.7.2 High concentration areas are those for which: Ambient PM10 data show ambient concentrations exceeding either PM10 NAAQS by 20 percent or more.
3.7.7.3 Medium concentration areas are those for which: Ambient PM10 data show ambient concentrations exceeding either 80 percent of the PM10 NAAQS.
3.7.7.4 Low concentration areas are those for which: Ambient PM10 data show ambient concentrations less than 80 percent of the PM10 NAAQS.
Table 5_Goals for Number of PM2.5 NAMS by Region
------------------------------------------------------------------------
Percent of National
EPA Region Number of NAMS \1\ Total
------------------------------------------------------------------------
1 15 to 20 6 to 8
2 20 to 30 8 to 12
3 20 to 25 8 to 10
4 35 to 50 14 to 20
5 35 to 50 14 to 20
6 25 to 35 10 to 14
7 10 to 15 4 to 6
8 10 to 15 4 to 6
9 25 to 40 10 to 16
10 10 to 15 4 to 6
-------------------------------------------------
Total 205-295 100
------------------------------------------------------------------------
\1\ Each region will have one to three NAMS having the monitoring of
regional transport as a primary objective.
4. Network Design for Photochemical Assessment Monitoring Stations (PAMS)
In order to obtain more comprehensive and representative data on O3 air pollution, the 1990 Clean Air Act Amendments require enhanced monitoring for ozone (O3), oxides of nitrogen (NO, NO2, and NOX), and monitoring for VOC in O3 nonattainment areas classified as serious, severe, or extreme. This will be accomplished through the establishment of a network of Photochemical Assessment Monitoring Stations (PAMS).
4.1 PAMS Data Uses. Data from the PAMS are intended to satisfy several coincident needs related to attainment of the National Ambient Air Quality Standards (NAAQS), SIP control strategy development and evaluation, corroboration of emissions tracking, preparation of trends appraisals, and exposure assessment.
(a) NAAQS attainment and control strategy development. Like SLAMS and NAMS data, PAMS data will be used for monitoring O3 exceedances and providing input for attainment/nonattainment decisions. In addition, PAMS data will help resolve the roles of transported and locally emitted O3 precursors in producing an observed exceedance and may be utilized to identify specific sources emitting excessive concentrations of O3 precursors and potentially contributing to observed exceedances of the O3 NAAQS. The PAMS data will enhance the characterization of O3 concentrations and provide critical information on the precursors which cause O3, therefore extending the database available for future attainment demonstrations. These demonstrations will be based on photochemical grid modeling and other approved analytical methods and will provide a basis for prospective mid-course control strategy corrections. PAMS data will provide information concerning (1) which areas and episodes to model to develop appropriate control strategies; (2) boundary conditions required by the models to produce quantifiable estimates of needed emissions reductions; and (3) the evaluation of the predictive capability of the models used.
(b) SIP control strategy evaluation. The PAMS will provide data for SIP control strategy evaluation. Long-term PAMS data will be used to evaluate the effectiveness of these control strategies. Data may be used to evaluate the impact of VOC and NOX emission reductions on air quality levels for O3 if data is reviewed following the time period during which control measures were implemented. Speciation of measured VOC data will allow determination of which organic species are most affected by the emissions reductions and assist in developing cost-effective, selective VOC reductions and control strategies. A State or local air pollution control agency can therefore ensure that strategies which are implemented in their particular nonattainment area are those which are best suited for that area and achieve the most effective emissions reductions (and therefore largest impact) at the least cost.
(c) Emissions tracking. PAMS data will be used to corroborate the quality of VOC and NOX emission inventories. Although a perfect mathematical relationship between emission inventories and ambient measurements does not yet exist, a qualitative assessment of the relative contributions of various compounds to the ambient air can be roughly compared to current emission inventory estimates to evaluate the accuracy of the emission inventories. In addition, PAMS data which are gathered year round will allow tracking of VOC and NOX emission reductions, provide additional information necessary to support Reasonable Further Progress (RFP) calculations, and corroborate emissions trends analyses. While the regulatory assessments of progress will be made in terms of emission inventory estimates, the ambient data can provide independent trends analyses and corroboration of these assessments which either verify or highlight possible errors in emissions trends indicated by inventories. The ambient assessments, using speciated data, can gauge the accuracy of estimated changes in emissions. The speciated data can also be used to assess the quality of the VOC speciated and NOX emission inventories for input during photochemical grid modeling exercises and identify potential urban air toxic pollutant problems which deserve closer scrutiny.
The speciated VOC data will be used to determine changes in the species profile, resulting from the emission control program, particularly those resulting from the reformulation of fuels.
(d) Trends. Long-term PAMS data will be used to establish speciated VOC, NOX, and limited toxic air pollutant trends, and supplement the O3 trends database. Multiple statistical indicators will be tracked, including O3 and its precursors during the events encompassing the days during each year with the highest O3 concentrations, the seasonal means for these pollutants, and the annual means at representative locations.
The more PAMS that are established in and near nonattainment areas, the more effective the trends data will become. As the spatial distribution and number of O3 and O3 precursor monitors improves, trends analyses will be less influenced by instrument or site location anomalies. The requirement that surface meteorological monitoring be established at each PAMS will help maximize the utility of these trends analyses by comparisons with meteorological trends, and transport influences. The meteorological data can also help interpret the ambient air pollution trends by taking meteorological factors into account.
(e) Exposure assessment. PAMS data will be used to better characterize O3 and toxic air pollutant exposure to populations living in serious, severe, or extreme areas. Annual mean toxic air pollutant concentrations will be calculated to help estimate the average risk to the population associated with individual VOC species, which are considered toxic, in urban environments.
4.2 PAMS Monitoring Objectives. Unlike the SLAMS and NAMS design criteria which are pollutant specific, PAMS design criteria are site specific. Concurrent measurements of O3, NOX, speciated VOC, and meteorology are obtained at PAMS. Design criteria for the PAMS network are based on selection of an array of site locations relative to O3 precursor source areas and predominant wind directions associated with high O3 events. Specific monitoring objectives are associated with each location. The overall design should enable characterization of precursor emission sources within the area, transport of O3 and its precursors into and out of the area, and the photochemical processes related to O3 nonattainment, as well as developing an initial, though limited, urban air toxic pollutant database. Specific objectives that must be addressed include assessing ambient trends in O3, NO, NO2, NOX, VOC (including carbonyls), and VOC species, determining spatial and diurnal variability of O3, NO, NO2, NOX, and VOC species and assessing changes in the VOC species profiles that occur over time, particularly those occurring due to the reformulation of fuels. A maximum of five PAMS sites are required in an affected nonattainment area depending on the population of the Metropolitan Statistical Area/Consolidated Metropolitan Statistical Area (MSA/CMSA) or nonattainment area, whichever is larger. Specific monitoring objectives associated with each of these sites result in four distinct site types. Note that detailed guidance for the locating of these sites may be found in reference 19.
Type (1) sites are established to characterize upwind background and transported O3 and its precursor concentrations entering the area and will identify those areas which are subjected to overwhelming transport. Type (1) sites are located in the predominant morning upwind direction from the local area of maximum precursor emissions during the O3 season and at a distance sufficient to obtain urban scale measurements as defined in section 1 of this appendix. Typically, type (1) sites will be located near the edge of the photochemical grid model domain in the predominant morning upwind direction from the city limits or fringe of the urbanized area. Depending on the boundaries and size of the nonattainment area and the orientation of the grid, this site may be located outside of the nonattainment area. The appropriate predominant morning wind direction should be determined from historical wind data occurring during the period 7 a.m. to 10 a.m. on high O3 days or on those days which exhibit the potential for producing high O3 levels, i.e., O3-conducive days as described in reference 25. Alternate schemes for specifying this morning wind direction may be submitted as a part of the network description required by §§58.40 and 58.41. Data measured at type (1) sites will be used principally for the following purposes:
• Future development and evaluation of control strategies,
• Identification of incoming pollutants,
• Corroboration of NOX and VOC emission inventories,
• Establishment of boundary conditions for future photochemical grid modeling and mid-course control strategy changes, and
• Development of incoming pollutant trends.
Type (2) sites are established to monitor the magnitude and type of precursor emissions in the area where maximum precursor emissions are expected to impact and are suited for the monitoring of urban air toxic pollutants. Type (2) sites are located immediately downwind of the area of maximum precursor emissions and are typically placed near the downwind boundary of the central business district to obtain neighborhood scale measurements. The appropriate downwind direction should be obtained similarly to that for type (1) sites. Additionally, a second type (2) site may be required depending on the size of the area, and should be placed in the second-most predominant morning wind direction as noted previously. Data measured at type (2) sites will be used principally for the following purposes:
• Development and evaluation of imminent and future control strategies,
• Corroboration of NOX and VOC emission inventories,
• Augmentation of RFP tracking,
• Verification of photochemical grid model performance,
• Characterization of O3 and toxic air pollutant exposures (appropriate site for measuring toxic emissions impact),
• Development of pollutant trends, particularly toxic air pollutants and annual ambient speciated VOC trends to compare with trends in annual VOC emission estimates, and
• Determination of attainment with the NAAQS for NO2 and O3.
Type (3) sites are intended to monitor maximum O3 concentrations occurring downwind from the area of maximum precursor emissions. Locations for type (3) sites should be chosen so that urban scale measurements are obtained. Typically, type (3) sites will be located 10 to 30 miles downwind from the fringe of the urban area. The downwind direction should also be determined from historical wind data, but should be identified as those afternoon winds occurring during the period 1 p.m. to 4 p.m. on high O3 days or on those days which exhibit the potential for producing high O3 levels. Alternate schemes for specifying this afternoon wind direction may also be submitted as a part of the network description required by §§58.40 and 58.41. Data measured at type (3) sites will be used principally for the following purposes:
• Determination of attainment with the NAAQS for O3 (this site may coincide with an existing maximum concentration O3 monitoring site),
• Evaluation of future photochemical grid modeling applications,
• Future development and evaluation of control strategies,
• Development of pollutant trends, and
• Characterization of O3 pollutant exposures.
Type (4) sites are established to characterize the extreme downwind transported O3 and its precursor concentrations exiting the area and will identify those areas which are potentially contributing to overwhelming transport in other areas. Type (4) sites are located in the predominant afternoon downwind direction, as determined for the type (3) site, from the local area of maximum precursor emissions during the O3 season and at a distance sufficient to obtain urban scale measurements as defined elsewhere in this appendix. Typically, type (4) sites will be located near the downwind edge of the photochemical grid model domain. Alternate schemes for specifying the location of this site may be submitted as a part of the network description required by §§58.40 and 58.41. Data measured at type (4) sites will be used principally for the following purposes:
• Development and evaluation of O3 control strategies,
• Identification of emissions and photochemical products leaving the area,
• Establishment of boundary conditions for photochemical grid modeling,
• Development of pollutant trends,
• Background and upwind information for other downwind areas, and
• Evaluation of photochemical grid model performance.
States choosing to submit an individual network description for each affected nonattainment area, irrespective of its proximity to other affected areas, must fulfill the requirements for isolated areas as described in section 4 of this appendix, as an example, and illustrated by Figure 5. States containing areas which experience significant impact from long-range transport or are proximate to other nonattainment areas (even in other States) should collectively submit a network description which contains alternative sites to those that would be required for an isolated area. Such a submittal should, as a guide, be based on the example provided in Figure 6, but must include a demonstration that the design satisfies the monitoring data uses and fulfills the PAMS monitoring objectives described in sections 4.1 and 4.2 of this appendix.
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Alternative PAMS network designs should, on a site-by-site basis, provide those data necessary to enhance the attainment/nonattainment database for criteria pollutants and explain the origins of overwhelming O3 transport. The alternative PAMS data should be usable for the corroboration and verification of O3 precursor emissions inventories and should comprise a qualitative (if not quantitative) measure of the accuracy of RFP calculations. The data should be sufficient to evaluate the effectiveness of the implemented O3 control strategies and should provide data necessary to establish photochemical grid modeling boundary conditions and necessary inputs including appropriate meteorological parameters, and provide measurements which can serve as model evaluation tools. Further, utilizing its PAMS database (alternative or not), a State should be able to draw conclusions regarding population exposure and conduct trends analyses for both criteria and non-criteria pollutants. Overall, the PAMS network should serve as one of several complementary means, together with modeling and analysis of other data bases (e.g., inventories) and availability of control technology, etc., for States to justify the modification of existing control programs, design new programs, and evaluate future courses of actions for O3 control.
4.3 Monitoring Period. PAMS precursor monitoring will be conducted annually throughout the months of June, July and August (as a minimum) when peak O3 values are expected in each area; however, precursor monitoring during the entire O3 season for the area is preferred. Alternate precursor monitoring periods may be submitted for approval as a part of the PAMS network description required by §58.40. Changes to the PAMS monitoring period must be identified during the annual SLAMS Network Review specified in §58.20. PAMS O3 monitors must adhere to the O3 monitoring season specified in section 2.5 of appendix D. To ensure a degree of national consistency, monitoring for the 1993 season should commence as follows:
One in 3-day sampling—June 3, 1993.
One in 6-day sampling—June 6, 1993.
These monitoring dates will thereby be coincident with the previously-established, intermittent schedule for particulate matter. States initiating sampling earlier (or later) than June 3, 1993 should adjust their schedules to coincide with this national schedule.
4.4 Minimum Monitoring Network Requirements. The minimum required number and type of monitoring sites and sampling requirements are based on the population of the affected MSA/CMSA or nonattainment area (whichever is larger). The MSA/CMSA basis for monitoring network requirements was chosen because it typically is the most representative of the area which encompasses the emissions sources contributing to nonattainment. The MSA/CMSA emissions density can also be effectively and conveniently portrayed by the surrogate of population. Additionally, a network which is adequate to characterize the ambient air of an MSA/CMSA often must extend beyond the boundaries of such an area (especially for O3 and its precursors); therefore, the use of smaller geographical units (such as counties or nonattainment areas which are smaller than the MSA/CMSA) for monitoring network design purposes is inappropriate. Various sampling requirements are imposed according to the size of the area to accommodate the impact of transport on the smaller MSAs/CMSAs, to account for the spatial variations inherent in large areas, to satisfy the differing data needs of large versus small areas due to the intractability of the O3 nonattainment problem, and to recognize the potential economic impact of implementation on State and local government. Population figures must reflect the most recent decennial U.S. census population report. Specific guidance on determining network requirements is provided in reference 19. Minimum network requirements are outlined in table 2.
Table 2_PAMS Minimum Monitoring Network Requirements \1\
------------------------------------------------------------------------
Minimum Minimum
Required speciated carbonyl
Population of MSA/CMSA or site type VOC sampling sampling
nonattainment area \2\ \3\ frequency frequency
\4\ \4\
------------------------------------------------------------------------
Less than 500,000.............. (\1\) A or C ............
(\2\) A or C D or F \5\
500,000 to 1,000,000........... (\1\) A or C ............
(\2\) B E
(\3\) A or C ............
1,000,000 to 2,000,000......... (\1\) A or C ............
(\2\) B E
(\2\) B E
(\3\) A or C ............
More than 2,000,000............ (\1\) A or C ............
(\2\) B E
(\2\) B E
(\3\) A or C ............
(\4\) A or C ............
------------------------------------------------------------------------
\1\ O3 and NOX (including NO and NO2) monitoring should be continuous
measurements.
\2\ Whichever area is larger.
\3\ See Figure 5.
\4\ Frequency Requirements are as follows: A_Eight 3-hour samples every
third day and one additional 24-hour sample every sixth day during the
monitoring period; B_Eight 3-hour samples, every day during the
monitoring period and one additional 24-hour sample every sixth day
year-round; C_Eight 3-hour samples on the 5 peak O3 days plus each
previous day, eight 3-hour samples every sixth day, and one additional
24-hour sample every sixth day, during the monitoring period; D_Eight
3-hour samples every third day during the monitoring period; E_Eight 3-
hour samples every day during the monitoring period; F_Eight 3-hour
samples on the 5 peak O3 days plus each previous day and eight 3-hour
samples every sixth day during the monitoring period. (NOTE: multiple
samples taken on a daily basis must begin at midnight and consist of
sequential, non-overlapping sampling periods.)
\5\ Carbonyl sampling frequency must match the chosen speciated VOC
frequency.
Note that the use of Frequencies C or F requires the submittal of an
ozone event forecasting scheme.
For purposes of network implementation and transition, EPA recommends the following priority order for the establishment of sites:
• The type (2) site which provides the most comprehensive data concerning O3 precursor emissions and toxic air pollutants,
• The type (3) site which provides a maximum O3 measurement and total conversion of O3 precursors,
• The type (1) site which delineates the effect of incoming precursor emissions and concentrations of O3 and provides upwind boundary conditions,
• The type (4) site which provides extreme downwind boundary conditions, and
• The second type (2) site which provides comprehensive data concerning O3 precursor emissions and toxic air pollutants in the second-most predominant morning wind direction on high O3 days.
Note also that O3 event (peak day) monitoring will require the development of a scheme for forecasting such high O3 days or will necessitate the stipulation of what meteorological conditions constitute a potential high O3 day; monitoring could then be triggered only via meteorological projections. The O3 event forecasting and monitoring scheme should be submitted as a part of the network description required by §§58.40 and 58.41 and should be reviewed during each annual SLAMS Network Review specified in §58.20. (continued)