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
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