- In a nutshell...
- As mandated by the 1990 Clean Air Act
Amendments, EPA is requiring more extensive monitoring of ozone
and its precursors in areas with persistently high ozone levels (mostly
large cities). The states must establish air monitoring sites, called
Photochemical Assessment Monitoring Stations, or PAMS, to collect and
report detailed data for volatile organic compounds, nitrogen oxides,
ozone, and meteorology. Analysis of the data will help EPA and the states
to understand better the underlying causes of ozone pollution, devise
effective remedies, and measure improvement.
Background
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.
OBJECTIVE 1
Provide a speciated ambient air database which is both representative and
useful for ascertaining ambient profiles and distinguishing among various
individual VOC. These data can later be used as evaluation tools for control
strategies, cost-effectiveness, and for understanding the mechanisms of
pollutant transport.
- DQO #1.1 The data for any given pollutant measured at a PAMS site
must be able to show the presence of a diurnal pattern, if one exists,
with an 80% confidence level.
- DQO #1.2 The data for any given pollutant measured at a PAMS site
must be able to show a change in the diurnal pattern, if a change exists,
with an 80% confidence level.
OBJECTIVE 2
Provide local, current meteorological and ambient data to serve as initial
and boundary condition information for photochemical grid models. These
data can later be used as a baseline for model evaluation and to minimize
model adjustments and reliance on default settings.
- DQO #2.1 The speciated VOC, ozone, NOx and meteorological data must
satisfy the regulations, including monitor siting, operation, and data
quality criteria.
OBJECTIVE 3
Provide a representative, speciated ambient air database which is characteristic
of source emission impacts. These data can be particularly useful in analyzing
emissions inventory issues and corroborating progress toward attainment.
- DQO #3.1 The monitoring data for Total Volatile Organic Compound (Total
VOC) concentrations collected at #2 Sites must be able to demonstrate
a 3% annual trend (upward or downward) over a 5-year monitoring period,
if it exists, with an 80% confidence level.
- DQO #3.2 The speciated VOC monitoring data collected at a #2 Site,
when composited into categories, must be able to demonstrate a 20% change
(upward or downward) in the seasonal average between two consecutive
years, if it exists, with an 80% confidence level.
OBJECTIVE 4
Provide ambient data measurements which would allow later preparation of
unadjusted and adjusted pollutant trends reports.
- DQO #4.1 The composite monitoring data for a given MSA/CMSA for ozone,
NOx, and speciated VOC must be able to demonstrate a yearly downward
trend with an 80% confidence level until an area achieves attainment.
OBJECTIVE 5
Provide additional measurements of selected criteria pollutants. Such measurements
can later be used for attainment/nonattainment decisions and to construct
NAAQS maintenance plans.
- DQO #5.1 The ozone (and NO2 where appropriate) monitoring data must
satisfy the criteria specified in the NAMS and SLAMS monitoring regulations,
including monitor siting, operation, and data quality criteria.
OBJECTIVE 6
Provide additional measurements of selected criteria and non-criteria pollutants
from properly-sited locations. Such measurements can later be used for evaluating
population exposure to air toxics as well as criteria pollutants.
- DQO 6.1 The speciated VOC monitoring data must be able to provide
annual average concentration data at #2 Sites to within +/-50%, with
a confidence level of 80%.
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:
 Site #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.
For More Information...
More complete and detailed information about enhanced ozone monitoring is
available from OAR's Technology Transfer Network (TTNWEB)
site.
International Symposium on Toxic Air Pollutants
The twelfth annual International Symposium on the Measurement of Toxic and
Related Air Pollutants co-sponsored by the U.S. Environmental Protection
Agency's National Exposure Research Laboratory (NERL) and the Air and Waste
Management Association (A&WMA;) will be held in Research Triangle Park, North
Carolina, April 29 -May 1, 1997. A special session has been set aside for
oral papers concerning the Photochemical Assessment Monitoring Stations
(PAMS) program, click here for more information.
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