EPA/600/A-97/031
Status of PAMS Meteorological Monitoring Activities
Gennaro H. Crescent!1 and Desmond T. Bailey2
Atmospheric Sciences Modeling Division
Air Resources Laboratory
National Oceanic and Atmospheric Administration
Research Triangle Park, North Carolina 27711
ABSTRACT
The Photochemical Assessment Monitoring Station (PAMS) requires surface and upper-air
meteorological data to assist in the development and evaluation of new ozone control strategies,
emissions tracking, trend analysis, exposure assessment, and numerical modeling. An emphasis is
placed on the acquisition of upper-air meteorological data. Wind and temperature profiles can be
obtained with in situ measurement systems such as expendable balloon systems (rawinsondes),
tethered balloon sondes, or with ground-based remote sensors such as Doppler sodars, radar wind
profilers, and radio acoustic sounding systems (RASS). This paper provides a summary of the
meteorological monitoring activities in support of PAMS planned for the 1997 summer ozone
season. The results of several air quality studies conducted in PAMS areas are cited as examples of
the importance of meteorological data in assessing ozone and precursor transport and dispersion.
INTRODUCTION
On February 12, 1993, the United States Environmental Protection Agency (EPA)
promulgated rules to establish enhanced ambient monitoring networks for ozone and ozone
precursors as required by Section 182 (c)(l) of the 1990 Clean Air Act Amendments. These
networks, known as Photochemical Assessment Monitoring Stations (PAMS), are required in ozone
nonattainment areas designated as serious, severe, and extreme. The PAMS requirements are
incorporated in the ambient air quality surveillance regulations (Title 40 Part 58 of the Code of
Federal Regulations). In addition to provisions for enhanced monitoring of ozone and its precursors,
surface and upper-air meteorological measurements must be made in each PAMS network.
The data gathered by PAMS are intended to enhance the ability of State and local air
pollution control agencies to effectively evaluate ozone nonattainment conditions and identify cost-
effective control strategies. The data will be used to evaluate, adjust, and provide input to the
photochemical grid models utilized by the States to develop ozone control strategies and demonstrate
their success; meteorological data of known accuracy are essential to this process.
A detailed knowledge of meteorological conditions is necessary to better understand the
mechanisms that are responsible for nonattainment episodes. Surface and upper-air meteorological
data can be used in statistical models to characterize distinct episode types and severity. Trajectory
models can be used to elucidate source-receptor relationships. A carefully designed network of
surface and upper-air meteorological sensors can provide information on the dynamical structure of
'On assignment to the National Exposure Research Laboratory, U. S. Environmental Protection Agency.
2On assignment to the Office of Air Quality Planning and Standards, U, S, Environmental Protection Agency.
-------
localized mesoscale circulations (sea/lake breeze, mountain valley flows) which are mechanisms for
mixing, transport, and dispersion. Upper-air meteorological data can be used to estimate the height
of the mixed layer. These data can also be used to infer the magnitude of vertical and lateral mixing
of the atmosphere which is a measure of pollutant dispersion. Hourly profiles of wind velocity and
temperature from ground-based remote sensors will improve numerical simulations from the Urban
Airshed Model (UAM) and other algorithms used to reproduce nonattainment episodes. This paper
provides a summary of the meteorological monitoring activities in support of PAMS planned for the
1997 summer ozone season. In addition, the results of several air quality studies conducted in
PAMS areas are cited as examples of the critical importance of utilizing meteorological data in
assessing ozone and precursor transport and dispersion.
METEOROLOGICAL PROGRAMS
Meteorological monitoring requirements are discussed in detail in Appendix N of the PAMS
Implementation Manual (U. S. Environmental Protection Agency, 1994). The required surface
measurements at all sites in each PAMS area include 10-m horizontal wind speed and wind
direction, air temperature, and relative humidity. Solar radiation, ultraviolet radiation, barometric
pressure, and precipitation measurements are required at one site in each PAMS area. Measurement
of these surface meteorological variables is normally accomplished with various types of in situ
sensors (U. S. Environmental Protection Agency, 1995). The required upper-air measurements in
the first several hundred meters of the boundary layer include horizontal wind speed and wind
direction, and air temperature at a representative location in each PAMS area. Estimation of the
mixed layer height is also recommended. As indicated in the PAMS Implementation Manual, "the
design of the upper-air monitoring program will depend upon region specific factors such that the
optimum design for a given PAMS region is expected to be some combination of remote sensing,
and conventional atmospheric soundings."
The guidance for acquisition of upper-air meteorological data provides considerable
flexibility with regard to both selection of the measurement system and the siting of that equipment.
In particular, the selection of a site for upper-air meteorological monitoring for PAMS is not
constrained by the location of the nonattainment area. A PAMS upper-air site may be located in a
different State and may serve multiple PAMS nonattainment areas. As described by Crescenti
(1994), several different types of measurement platforms may used to acquire upper-air
meteorological data. These include aircraft, tall towers (typically up to 500 to 600 m), expendable
balloon systems (rawinsondes), tethered balloon sondes, and ground-based remote profilers such as
Doppler sodars, radar wind profiler, and radio acoustic sounding systems (RASS). Wind speed,
wind direction, air temperature, and relative humidity data can be easily measured by aircraft, tower-
mounted sensors, and balloon sondes. Doppler sodars and radar wind profilers acquire wind speed
and wind direction, while RASS collect profiles of temperature. The backscattered signal from
either a sodar or radar wind profiler is also useful in tracking the height of the mixed layer. As with
any measurement system, each has advantages and disadvantages. A detailed overview of these
remote sensor technologies is given by Clifford et al. (1994).
A minimum of four soundings per day is recommended to monitor the growth of the
convective boundary layer. These profiles should be acquired just prior to sunrise when the
atmospheric boundary layer is most stable; in mid-morning when the growth of the boundary layer
is most rapid; during mid-afternoon when surface temperatures are maximum; and in late-afternoon
when the boundary layer depth is largest. In special cases, an upper-air monitoring plan may be
-------
augmented with data from a nearby National Weather Service (NWS) station which launches
rawinsondes twice per day (00 and 12 GMT).
Table 1 summarizes the PAMS upper-air meteorological monitoring programs either in place
or expected to be in place for the 1997 summer ozone season. Included in the table is the EPA
Region, affected area, classification, the minimum number of surface sites required for that area, the
type of upper-air measurement platform, owner and/or operator responsible for maintaining the
platform, and the status of the monitoring program. Blank cells in the table mean that no
information is currently available. Figure 1 shows the locations of these sites. As of this writing,
fourteen radar/RASS systems, seven Doppler sodars, and two rawinsonde programs are expected to
be in used in support of PAMS during the 1997 summer ozone season. The ground-based remote
sensors are configured to acquire profiles of wind and temperature data as one-hour averages. A
rawinsonde program is operated at Baton Rouge by the Louisiana Department of Environmental
Quality (LDEQ); this program provides four rawinsonde releases per day on forecast episode days
during the ozone season. All PAMS networks have access to the twice-per-day rawinsonde data
provided by the NWS. The PAMS network for Atlanta, for example, makes use of the NWS
rawinsonde data acquired at Peachtree City, Georgia.
PREVIOUS AIR QUALITY STUDIES IN PAMS AREAS
The use of upper-air data has lead to a better understanding of the mechanisms which lead
to ozone exceedences. Ground-based remote sensors are especially valuable since they are capable
of resolving the temporal variability of the atmosphere on time scales of less than an hour. When
configured into a network, these sensors are capable of resolving spatial variability of the atmosphere
on the order of several tens of kilometers. The following are examples of how these technologies
have been used in urban areas which experience ozone exceedences.
The 1991 Lake Michigan Ozone Study (LMOS) included a comprehensive field
measurement program to gather data to understand the complex meteorology and air quality of the
Lake Michigan Air Quality Region (LMAQR) and to verify predictions from air quality models (Dye
et al., 1995). The LMAQR, which encompasses parts of Wisconsin, Illinois, Indiana, and Michigan,
experiences ozone concentrations that exceed the National Ambient Air Quality Standard (NAAQS)
of 120 ppb in urban and rural areas primarily during the summer. Most of the local ozone precursor
emissions originate in the urban and industrial areas of northern Indiana (i.e., Gary), northeastern
Illinois (i.e., Chicago), and southeastern Wisconsin (i.e., Milwaukee) (Dye et al., 1995). The highest
ozone concentrations typically occur along the Wisconsin and Michigan shorelines.
The LMOS measurement program included a sodar, seven radar wind profilers, seven
rawinsonde sites, and research aircraft. Dye et al. (1995) were able to develop a five-stage
conceptual model of ozone and precursor transport from this network of upper-air observations
around and over Lake Michigan. First, the land breeze and general offshore flow (i.e., southerly to
west-southwesterly winds) during the early morning transported emissions confined in the stable
nocturnal boundary layer into the stable air (conduction layer) over Lake Michigan. Second, a sharp
horizontal temperature gradient developed by 0900 CDT along the western shoreline and effectively
cut off additional injections of shore-emitted precursors into the conduction layer over the lake. The
strong stability of the conduction layer limited pollutant dispersion. Third, by midmorning, the
developing convective boundary layer grew as convection vertically mixed ozone. Next, the
prevailing winds transported polluted air to the downwind receptor regions which were either the
Wisconsin or Michigan shorelines depending on the large-scale wind flow. Finally, when the ozone-
-------
laden air flowed onshore at the downwind receptor regions, air with the highest ozone concentrations
located in approximately the first 300 m of the atmosphere mixed down (fumigated) to the surface
first, causing the highest ozone concentrations along the shoreline. Eventually, air from higher
altitudes mixed down to the surface farther inland, but ozone concentrations in these air masses had
lower concentrations.
The 1992 Atlanta Field Intensive was designed to investigate the various chemical and
meteorological factors leading to the continued exceedences of the NAAQS for ozone in and around
the city of Atlanta, Georgia (Marsik et al., 1995). Intensive chemical and meteorological
measurements were made on a series of eight ozone exceedence days from mid-July to late-August.
The upper-air meteorological systems used in this study included three wind profiling radars with
RASS, two aerosol lidars, and a rawinsonde system. These data were used to determine the mixing
height of the planetary boundary layer. This parameter is of particular importance to air pollution
modelers. The ability of photochemical and dispersion models to accurately predict surface pollutant
concentrations is dependent upon the accurate representation of the time-varying mixing height.
This is because the mixing height determines the effective volume in which chemical reactions take
place. Overall, the rawinsonde appeared to give the most accurate mixing height estimates. The
radar wind profiler estimates were found to be erroneously high during the early morning hours due
mainly to the use of a setup configuration that precluded detection on the newly developing mixed
layer below 400 to 600 m. However, during the day under convective conditions, estimates of the
mixing height from the radar wind profiler were comparable to that of the rawinsonde.
Two regional air quality studies were conducted in southeast Texas and Louisiana during the
summer of 1993 to collect meteorological and air quality data to analyze conditions that lead to
exceedences of Federal and State ozone standards and to support meteorological and photochemical
modeling studies of these ozone episodes (Lindsey et al,, 1994, 1995). The Gulf of Mexico Air
Quality Study (GMAQS) and the Coastal Oxidant Assessment in Southeast Texas (COAST) project
employed a network of seven radar/RASS systems. Lindsey et al. (1994, 1995) found that every
ozone exceedence was associated with a reversal of the sea breeze/land breeze circulation. Days on
which the flow reversal did not occur were generally non-exceedence days. Normally, the weak land
breeze (offshore flow) during the early morning hours is nonexistent since the local thermal
gradients set up by the land/sea temperature difference is not large enough to overcome the large-
scale, synoptically forced southwesterly flow of the Bermuda high pressure system. However, they
speculated that when the Bermuda high moved westward, the synoptic scale gradients weaken
allowing for the formation of the land breeze during the evenings. When this happened, the land
breeze would push the polluted air from the Houston airshed offshore. This polluted air would be
pushed back onshore during the next day with the onset of the sea breeze, thereby adding to the
locally-generated ozone in the Houston area. It is clear from the analysis by Lindsey et al. (1995)
that without the hourly-averaged radar wind profiles, it would have been difficult to assess what
mechanisms were responsible for the ozone exceedences.
An array of four radar/RASS systems were deployed in the northeastern United States in the
summer of 1994 to acquire upper-air data (Lindsey et al., 1996). These sensors were located in New
Brunswick, New Jersey, Bermudian Valley, Pennsylvania, Schenectady, New York, and Bridgeport,
Connecticut. The profiles of wind, temperature, and backscatter intensity were used to examine the
mesoscale and synoptic scale processes that influence ozone and precursor transport. Analyses
showed that on ozone exceedence days, growth of the convective mixed layer was slower than on
prior days. This slower growth confined morning emissions to a shallower layer. Consequently,
-------
photochemistry likely occured in the presence of higher precursor concentrations. During the
evening, the surface-based nocturnal boundary layer would develop to a depth of about 200 m.
Between the top of the nocturnal boundary layer and the top of the previous day's convective
boundary layer, a residual layer developed. This decoupled layer, which contained high
concentrations of ozone and precursors, was effectively cut off from surface processes that might
have titrated ozone concentrations. The moderate stability of this layer probably limited further
diffusion until vigorous convective mixing to the surface (fumigation) during the next day. Within
this decoupled layer, a low-level jet was observed at the profiler sites on all nights preceding an
exceedence day. The core of the jet was usually centered between 400 and 800 m above the ground
with velocities ranging between 5 to 15 m s"1 from the southwest to west-southwest. Lindsey et al.
(1996) speculated that this low-level jet was capable of transporting ozone and its precursors over
long distances during the evening. Once again, with out the aid of hourly wind and temperature data
from the radar/RASS, it would have been difficult to determine the exact nature of this decoupled
layer and low-level jet.
SUMMARY
This paper has presented a brief overview of the various PAMS meteorological monitoring
activities with an emphasis placed on the upper-air monitoring components. Most of the
implementing agencies are using ground-based remote sensors such as Doppler sodars, radar wind
profilers, and radio acoustic sounding systems to acquire upper-air information necessary to better
understand the mechanisms that are responsible for nonattainment episodes. The results of several
air quality studies conducted in PAMS areas have been cited as examples of the critical importance
of upper-air meteorological data in assessing ozone and precursor transport and dispersion.
DISCLAIMER
This document has been reviewed in accordance with U. S. Environmental Protection
Agency policy and approval for publication. Mention of trade names or commercial products does
not constitute EPA endorsement or recommendation for use.
REFERENCES
Clifford, S. F.; Kaimal, J. C.; Lataitis, R. J.; Strauch, R. G. "Ground-based remote profiling in the
atmospheric studies: An overview." Proc. IEEE 1994 8.2, 313-355.
Crescenti, G. H. "Overview of PAMS meteorological monitoring requirements," in Proceedings of
the EPAJAWMA Symposium on Measurement of Toxic and Related Air Pollutants, Air &
Waste Management Association, Durham, NC, 1994, 245-253.
Dye, T. S,; Roberts, P. T.; Korc, M. E. "Observations of transport processes for ozone and ozone
precursors during the 1991 Lake Michigan Ozone Study," J. Appl. Meteor. 1995 34,1877-
1889.
Lindsey, C. G.; Dye, T. S.; Anderson, J. A.; Wolfe, D. E. "Observations of the marine boundary
layer over southeast Texas and the Gulf of Mexico using 915 MHz radar profiler and RASS,"
in Preprints of the Eighth Symposium on Air Pollution Meteorology with the AW MA, Amer.
Meteor. Soc., Nashville, TN, 1994,301-308.
Lindsey, C. G.; Dye, T. S.; Roberts, P. T.; Anderson, J. A.; Ray, S. E. "Meteorological aspects of
ozone episodes in southeast Texas," in Proceedings of the 88th Annual Meeting &
Exhibition, Air & Waste Management Association, San Antonio, TX, 1995, paper TP15P.03.
-------
Lindsey, C. G.; Dye, T. S.; Blumenthal, D. L.; Ray, S. E.; Arthur, M. "Meteorological aspects of
summertime ozone episodes in the northeast," in Preprints of the Ninth Symposium on Air
Pollution Meteorology with the AW MA, Amer. Meteor. Soc., Atlanta, GA, 1996, 233-237.
Marsik, F. J.; Fischer, K. W.; McDonald, T. D.; Samson, P. J. "Comparison of methods for
estimating mixing height used during the 1992 Atlanta Field Intensive." J. Appl. Meteor.
199524,1802-1814.
U. S. Environmental Protection Agency. Photochemical Assessment Monitoring Stations
Implementation Manual. EPA-454/B-93-051, Research Triangle Park, NC, 1994.
U. S. Environmental Protection Agency. Quality Assurance Handbook for Air Pollution
Measurement Systems. Volume IV: Meteorological Measurements. EPA-600/4-90-003,
Research Triangle Park, NC, 1995.
Sodar
Rawinsonde
Radar/RASS Wind Profiler
PAMS Area
Figure 1. PAMS upper-air meteorological monitoring locations.
-------
Table 1. PAMS Upper-Air Meteorological Sites and Systems.
Re-
§ion
1
I
I
I
I
11
111
III
HI
IV
V
V
VI
VI
VI
Affected Area
Portsmouth
Springfield
Providence
Boston
Greater Connecticut
New York
Washington, D. C.
Baltimore
Philadelphia
Atlanta
Milwaukee
Chicago
Beaumont2
Baton Rouge
El Paso
Class-
ification
Serious
Serious
Serious
Serious
Serious
Severe
Serious
Severe
Severe
Serious
Severe
Severe
Serious
Serious
Serious
Min.
Sites
2
3
4
5
5
5
5
5
5
5
4
5
2
3
3
Location
Boston
Millstone Point
New Brunswick
Redhook
Baltimore
Gettysburg
Holbrook
Peachtree City
Waukegan
Jefferson County Airport
Baton Rouge
Univ. Texas - El Paso
Lower Valley
Sun Metro
NW site
Upper-air
System
radar/RASS
radar/RASS
radar/RASS
radar/RASS
radar/RASS
radar/RASS
radar/RASS
rawinsonde1
sodar
radar/RASS
rawinsonde3
radar/RASS
sodar
sodar
sodar
Owner/Operator
State of Massachusetts
Northeast Utilities
Rutgers University
NARSTO-NE
University of Maryland
NARSTO-NE
NARSTO-NE
NWS
1L Dept. Nuclear Safety
TNRCC
LDEQ
UTEP
TNRCC
TNRCC
TNRCC
Status
pending 97
inactive
active
ended Aug. 96
pending 97
ended Aug. 96
ended Aug. 96
active
active
active
active
active
active
pending 98
-------
Table 1. (continued)
Re-
gion
VI
VI
VII
IX
IX
IX
IX
IX
IX
Affected Area
Houston
Dallas4
St. Louis"
Southeast Desert Air Basin
Ventura County
Sacramento
San Joaquin Valley
San Diego
Los Angeles
Class-
ification
Severe
Severe
Severe
Serious
Serious
Severe
Extreme
Min.
Sites
5
2
3
4
5
5
5
Location
Clear Lake City
Galveston Airport
Wharton Power Plant
Ship channel
Dallas/Fort Worth Airport
Upwind rural site
Hinton
Denton Airport
Simi Valley Landfill
Franklin Field
Hanford/Lemoore
Point Loma NAS
Los Angeles Int. Airport
Ontario County Airport
Upper-air
System
radar/RASS
sodar
sodar
sodar
radar/RASS
sodar
sodar
sodar
radar/RASS
radar/RASS
radar/RASS
radar/RASS
radar/RASS
radar/RASS
Owner/Operator
TNRCC
TNRCC
TNRCC
TNRCC
TNRCC
TNRCC
TNRCC
TNRCC
VCAPCD
SMAQMD
SJVAPCD
SDAPCD
SCAQMD
SCAQMD
Status
pending 97
active
active
pending 98
pending 98
pending 98
active
active
active
pending 96
pending 97
active
active
active
'Rawinsondes launched two times per day by NWS.
Declassified on June 1,1996 to moderate nonattainment status and therefore not required to implement PAMS program.
3Rawinsondes launched four times per day by LDEQ on nonattainment days during ozone season.
4Pending classification to nonattainment status.
-------
TECHNICAL REPORT DATA
REPORT NO.
600/A-97/031
2.
4. TITLE AND SUBTITLE
Status of PAMS Meteorological Monitoring Activities
5.REPORT DATE
6.PERFORMTNG ORGANIZATION CODE
7. AUTHOR(S)
CRESCENT!, Gennaro H., and BAILEY, Desmond T.
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Same as Block 12
10.PROGRAM ELEMENT NO.
II. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/9
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The Photochemical Assessment Monitoring Station (PAMS) requires si'rface and upper-air meteorological data to assist in the
development and evaluation of new ozone control strategies, emissions tracking, trend analysis, exposure assessment, and
numerical modeling. An emphasis is placed on the acquisition of upper-air meteorological data. Wind and temperature profiles
can be obtained with in silu measurement systems such as expendable balloon systems (rawinsondes), tethered balloon sondes, or
with ground-based remote sensors such as Doppler sodars, radar wind profilers, and radio acoustic sounding systems (RA.SS).
This paper provides a summary of the meteorological monitoring activities in support of PAMS planned for the 1997 summer
ozone season. The results of several air quality studies conducted in PAMS areas are cited as examples of the importance of
meteorological data in assessing ozone and precursor transport and dispersion.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
^IDENTIFIERS/ OPEN ENDED TERMS
c.COSATI
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21.NO. OF PAGES
20. SECURITY CLASS (This Page)
UNCLASSIFIED
22. PRICE
------- |