United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S9-85/008 Apr. 1985
Project Summary
Conceptual Design for a
Gulf Coast Oxidant Transport
and Transformation Experiment:
Workshop Proceedings and
Recommendations
Walter F. Dabberdt, William Viezee, and Hanwant B. Singh
The transport of ozone and oxidant-
precursor emissions from the in-
dustrial areas of the Gulf Coast to
other areas of the United States, par-
ticularly the Northeast and Midwest,
may exacerbate documented smog
problems in those areas. The extent of
this transport is unknown. This docu-
ment presents the output of a
workshop held in Durham, NC,
November 1982, to develop a concep-
tual design for a Gulf Coast transport
and transformation experiment. It
outlines a field study designed to
quantify the amounts of material in-
jected into the large-scale flow and
the amount remaining in the Gulf
Coast area. Results of the field study
will help to describe such transport,
and aid in the application of the
Regional Oxidant Model to the Gulf
Coast area to perform sensitivity
studies on the regional transport of
ozone and precursors.
This Project Summary was devel-
oped by EPA's Atmospheric Sciences
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is ful-
ly documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction and Discussion
The basic objective of a Gulf Coast oxi-
dant study would be to "investigate the
unique meteorological and chemical proc-
esses in the Gulf Coast region that must
be understood to effectively adapt the
EPA Regional Oxidant Model to that
geographical area." Some of the more im-
portant and relevant processes to be
studied include
• Three-dimensional transport by land-
breeze and sea-breeze circulations
• Transport and diffusion under near-
stagnation conditions
• Ozone (and precursor) venting or
mixing by precipitating and non-
precipitating cumulus clouds
• Washout of nitrogeneous and oxy-
genated species and the impact on
oxidant production
• Parameterization of the over-water at-
mospheric surface layer
• Large-scale inflow to and outflow
from the region
• Investigation of anomalously low
values of the ratios of NOX/NMHC
and PAN/Os and the concentration
of PAN
• Nocturnal NO,, removal and trans-
formation mechanisms.
Thirty atmospheric scientists from
government, industry, academia, and the
private research sector participated in a
3-day workshop to develop a conceptual
design for the field study. Two working
groups were formed, focusing on prob-
lems of meteorology and atmospheric
chemistry, and measurement needs and
methods.
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Atmospheric Chemistry
The atmospheric chemistry working
group addressed and prioritized the trace
chemicals that must be measured during
any planned Gulf Coast oxidant study.
The exact platforms to be employed, fre-
quency of measurements, and spatial den-
sity of monitoring stations were issues
which could not be considered by the
working group since a detailed design of
the Gulf Coast study did not exist. The
group, therefore, focused on broader con-
siderations dealing with trace chemical
measurements and emissions data re-
quirements.
Trace chemical measurements (both
gas and liquid phases) were identified and
ranked according to the importance and
feasibility of the measurements. Among
the nonchemical parameters, liquid water
content and ultraviolet radiation measure-
ments were highly emphasized. It was
generally believed that gas-phase proc-
esses provide the dominant source for
ozone formation and hence constitute the
most important measurements. The roles
of aldehydes and H202 in liquid phases is
not well understood but may be potential-
ly important. Nitrate measurements in the
aqueous phase were ranked high because
of the sink potential of the aqueous phase
for N02 and HNO3. Despite the recog-
nized importance of gas-phase chemistry,
the working group felt that liquid-phase
processes may play a more important role
in the wet and humid environment of the
Gulf Coast, as compared to relatively dry
regions.
Tracers of opportunity were suggested,
but only chlorofluorocarbons were con-
sidered high priority. 'Be or 33P
stratospheric tracers were ranked low, in
part because of the complexity of data in-
terpretation. Injected specialty tracers are
unique tools to study long-range
transport, but are to be measured only
when a planned tracer experiment is
under way.
Recommendations and guidelines were
developed for the emissions data required
for input to the Regional Oxidant Model
(ROM) or other photochemical models;
these included
• A 2-km by 2-km gridded inventory of
emissions
• Hourly temporal resolution, i.e., diur-
nal and seasonal emission patterns
• Vertical resolution of emissions
sources
• Source types (stationary, mobile,
area, point, natural, etc.)
• Natural volatile organic compounds
(VOCs) on land
• Gulf Coast water emissions.
It was recommended that some sen-
sitivity studies should be performed with
existing models to estimate the im-
portance of source emissions, particularly
natural VOCs of land or water origin. One
of the most pernicious problems is the
very nature of the emissions inventory. In
principle, emissions data (temporally and
spatially resolved) should be available for
individual species. This is not possible in
practice. Current models can use groups
of chemicals (alkanes, alkenes, and
aromatics) and this is a desirable specia-
tion of emission data. It was suggested,
however, that carbon bond mechanisms
may be employed in a future version of
ROM.
Meteorology
The meteorology working group
discussed a wide range of atmospheric
circulations and phenomena which were
judged to be potentially important in
determining oxidant concentrations in the
Gulf Coast and interior regions down-
wind; these features included
• Land-breeze and sea-breeze circula-
tions
• Convective cumulus cloud venting
• Synoptic-scale transport and disturb-
ances
• Surface deposition and destruction
• Synoptic-scale subsidence
• Characteristics of planetary layer over
the Gulf of Mexico.
On the basis of these discussions, the
working group made recommendations
and developed conceptual designs for a
mesoscale sea-breeze experiment, a
medium-range transport study, and an
enhanced monitoring network.
An Eulerian box-budget experiment
would be carried out for the sea-breeze
study in a rectangular area, 300 km north-
to-south, and 200 to about 400 km east-
to-west. This area would include the sea-
breeze circulation and coastal emission
sources of the Houston-Galveston-Lake-
Charles area. The box would be 3 km
deep (the average depth of the sea
breeze).
The sea-breeze program should also in-
clude studies of venting by cumulonimbus
and cumulus congestus clouds that form
in the afternoon inland along the sea-
breeze convergence zone. This zone
roughly parallel to the coastline is fairly
lengthy and these clouds occur with high
frequency. Therefore, these clouds may
be an effective mechanism for transport
of ozone precursors out of the Gulf Coast
emissions source region, thereby minimiz-
ing local ozone formation but impacting
regions further downwind. It was recom-
mended that an inert gas tracer would be
a useful tool for quantifying the effects of
cumulus-cloud venting.
An intermediate-range oxidant transport
experiment would involve a total time of
30 to 48 h for atmospheric measurements.
The experiment would cover a horizontal
distance of 400 to 500 km from the Gulf
Coast emissions source, which would take
the experiment from the Houston-
Galveston area northward into Oklahoma
and Arkansas. It would focus on ozone
and its precursors, and on released
tracers. The intermediate transport experi-
ment would take place under conditions
of synoptic-scale southerly flow,
preferably during the occurrence of a noc-
turnal low-level jet.
A wide variety of in situ and remote
measurement systems were considered
necessary for successful completion of
the sea-breeze and intermediate-range
transport experiment; these included air-
borne backscatter and differential-
absorption laser radar (lidar) systems, air-
borne Doppler radar and ground-based
Doppler sodar, in situ aerometric sampling
aircraft, and meteorological profiling
systems.
The work group recommended that an
enhanced network of surface and upper-
air observations be operated throughout
the time period that the mesoscale sea-
breeze and intermediate-range transport
programs are conducted. The network
area was outlined as extending from Fon
Worth, Texas, eastward to the Alabama
border (about 300 km), and then 600 km
southward to a point approximately 20C
km offshore. The existing Nationa
Weather Service (NWS) radiosonde sta-
tions within the network area (about six]
would be enhanced by five or six addi-
tional stations, including two stations off
shore, to double the spatial resolution o
the NWS network. Vertical profiles o
ozone would be obtained to 700 mba
(10,000 ft MSL) by single-engine aircraf
at each of 12 available radiosonde loca
tions. The network would be operated fo
a 3-month period.
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Walter F. Dabberdt, William Viezee, and Hanwant B. Singh are with SRI
International, Menlo Park, CA 94025.
Jason K. S. Ching is the EPA Project Officer (see below).
The complete report, entitled "Conceptual Design for a Gulf Coast Oxidant
Transport and Transformation Experiment: Workshop Proceedings and
Recommendations,"(OrderNo. PB85-173 789/AS; Cost:$11.50, subjectto
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
U.S. GOVERNMENT PRINTING OFFICE: 1985-559-016/27036
United States
Environmental Protection
Agency
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