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Photochemical Assessment Monitoring Stations (PAMS)


General Information

Network and Sites

Guidance Documents

Data Analysis and Reports

PAMS Re-Engineering


Section 182(c)(1) of the 1990 Clean Air Act Amendments (CAAA) required the Administrator to promulgate rules for the enhanced monitoring of ozone, oxides of nitrogen (NOx), and volatile organic compounds (VOC) to obtain more comprehensive and representative data on ozone air pollution. Immediately following the promulgation of such rules, the affected States were to commence such actions as were necessary to adopt and implement a program to improve ambient monitoring activities and the monitoring of emissions of NOx and VOC. Each State Implementation Plan (SIP) for the affected areas must contain measures to implement the ambient monitoring of such air pollutants. The subsequent revisions to Title 40, Code of Federal Regulations, Part 58 (40 CFR 58) required States to establish Photochemical Assessment Monitoring Stations (PAMS) as part of their SIP monitoring networks in ozone nonattainment areas classified as serious, severe, or extreme.

The principal reasons for requiring the collection of additional ambient air pollutant and meteorological data are the lack of attainment of the National Ambient Air Quality Standard (NAAQS) for ozone nationwide, and the need for a more comprehensive air quality database for ozone and its precursors.

The chief objective of the enhanced ozone monitoring revisions is to provide an air quality database that will assist air pollution control agencies in evaluating, tracking the progress of, and, if necessary, refining control strategies for attaining the ozone NAAQS. Ambient concentrations of ozone and ozone precursors will be used to make attainment/nonattainment decisions, aid in tracking VOC and NOx emission inventory reductions, better characterize the nature and extent of the ozone problem, and prepare air quality trends. In addition, data from the PAMS will provide an improved database for evaluating photochemical model performance, especially for future control strategy mid-course corrections as part of the continuing air quality management process. The data will be particularly useful to States in ensuring the implementation of the most cost-effective regulatory controls.

Data Quality Objectives

Data Quality Objectives (DQOs) are statements that relate the quality of environmental measurements to the level of uncertainty that decision-makers are willing to accept for results derived from the data. It is never possible to be absolutely certain that a future data set will satisfy the data needs exactly. There is always a chance that variables, variation, and uncertainty beyond the program's control will lead to a "softness" in the data and a resulting uncertainty that the subsequent decisions are appropriate. For example, it is not possible to be 100% certain that a downward trend in ozone concentration has been confirmed or denied, since it is possible that local meteorology unexpectedly affected the two highest-reading days, one way or the other. By carefully designing the equipment and schedules, however, it is possible to reduce to acceptable levels the possibility of making an erroneous call.

PAMS Site Descriptions

The PAMS network array for an area should be fashioned to supply measurements which will assist States in understanding and solving ozone nonattainment problems. EPA has determined that for the larger areas, the minimum network which will provide data sufficient to satisfy a number of important monitoring objectives should consist of five sites:

PAMS Network DesignSite #1 - Upwind and background characterization site. These sites are established to characterize upwind background and transported ozone and its precursor concentrations entering the area and will identify those areas which are subjected to overwhelming incoming transport of ozone. The #1 Sites are located in the predominant morning upwind direction from the local area of maximum precursor emissions and at a distance sufficient to obtain urban scale measurements. Typically, these sites will be located near the upwind edge of the photochemical grid model domain.

Site #2 - Maximum ozone precursor emissions impact site. These sites are established to monitor the magnitude and type of precursor emissions in the area where maximum precursor emissions representative of the MSA/CMSA are expected to impact and are suited for the monitoring of urban air toxic pollutants. The #2 Sites are located immediately downwind (using the same morning wind direction as for locating Site #1) of the area of maximum precursor emissions and are typically placed near the downwind boundary of the central business district (CBD) or primary area of precursor emissions mix to obtain neighborhood scale measurements. Additionally, a second #2 Site may be required depending on the size of the area, and should be placed in the second-most predominant morning wind direction.

Site #3 - Maximum ozone concentration site. These sites are intended to monitor maximum ozone concentrations occurring downwind from the area of maximum precursor emissions. Locations for #3 Sites should be chosen so that urban scale measurements are obtained. Typically, these sites are located 10 to 30 miles from the fringe of the urban area.

Site #4 - Extreme downwind monitoring site. These sites are established to characterize the extreme downwind transported ozone and its precursor concentrations exiting the area and will identify those areas which are potentially contributing to overwhelming ozone transport into other areas. The #4 Sites are located in the predominant afternoon downwind direction from the local area of maximum precursor emissions at a distance sufficient to obtain urban scale measurements. Typically, these sites will be located near the downwind edge of the photochemical grid model domain.

Areas Subject to PAMS

In 1997, the revision to the O3 NAAQS set forth that the 1-hour standards will no longer apply to an area once EPA determines that the area has air quality data meeting the 1-hour standards. Subsequent to that change, EPA revoked the 1-hour O3 NAAQS in most counties in the United States, leaving 226 counties (and 38 nonattainment areas) where the 1-hour standard still applies. Currently, 24 of the 38 1-hour ozone nonattainment areas are classified as either serious, severe, or extreme and hence, are subject to PAMS. The 24 areas have a total population of about 84 million people. Because the flexibility of the PAMS regulations allow areas in close proximity to one another to consolidate their monitoring operations, only 22 operating networks actually exist. See Area List and table endnotes in the Networks and Sites section.

PAMS Target Parameters

The data collected at the PAMS sites include measurements of O3, NOx, a target list of VOCs including several carbonyls, as well as surface and upper air meteorology. Most PAMS sites measure 56 target hydrocarbons on either a hourly or 3-hour basis during the O3 season. The Type 2 sites also collect data on 3 carbonyl compounds (formaldehyde, acetaldehyde, and acetone) every three hours during the O3 monitoring period. Included in the monitored VOC species are ten compounds classified as hazardous air pollutants (HAPs). All stations must measure O3, NOx, and surface meteorological parameters on an hourly basis. Below are the parameters monitored at the surface PAMS sites.

Ozone, nitrogen oxides, VOC sums Surface Meteorological
Ozone 44201 Temperature 62101
Wind Speed 61101/3
Nitric Acid 42601 Wind Direction 61102/4
Nitrogen Dioxide 42602 Relative Humidity 62201
Oxides of Nitrogen 42603 Solar Radiation 63301
uv Radiation 63302/4
Total NMOC 43102 Barometric Pressure 64101
Sum of Targeted HCs 43000 Precipitation 65102
Hydrocarbons (HCs) - listed in elution sequence
Ethylene 43203 2,3-dimethylpentane 43291
Acetylene 43206 3-methylhexane 43249
Ethane 43202 2,2,4-trimethylpentane 43250
Propylene 43205 n-Heptane 43232
Propane 43204 Methylcyclohexane 43261
Isobutane 43214 2,3,4-trimethylpentane 43252
1-Butene 43280 Toluene 45202
n-Butane 43212 2-methylheptane 43960
t-2-Butene 43216 3-methylheptane 43253
c-2-Butene 43217 n-Octane 43233
Isopentane 43221 Ethylbenzene 45203
1-Pentene 43224 m&p-Xylenes 45109
n-Pentane 43220 Styrene 45220
Isoprene 43243 o-Xylene 45204
t-2-pentene 43226 n-Nonane 43235
c-2-pentene 43227 Isopropylbenzene 45210
2,2-Dimethylbutane 43244 n-Propylbenzene 45209
Cyclopentane 43242 m-Ethyltoluene 45212
2,3-dimethylbutane 43284 p-Ethyltoluene 45213
2-methylpentane 43285 1,3,5-Trimethylbenzene 45207
3-Methylpentane 43230 o-Ethyltoluene 45211
2-Methyl-1-Pentene 43246 1,2,4-trimethylbenzene 45208
n-hexane 43231 n-Decane 43238
Methylcyclopentane 43262 1,2,3-trimethylbenzene 45225
2,4-dimethylpentane 43247 m-Diethylbenzene 45218
Benzene 45201 p-Diethylbenzene 45219
Cyclohexane 43248 n-Undecane 43954
2-methylhexane 43263
Formaldehyde 43502
Acetone 43551
Acetaldehyde 43503


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