United States
                    Environmental  Protection
                    Agency
Atmospheric Sciences
Research Laboratory              SI
Research Triangle Park NC 27711
                    Research and Development
EPA/600/S3-85/013 Apr. 1985
&ER&         Project  Summary
                    Ozone   Production  and   Transport
                    in   the  Atlanta,   Georgia   Region
                     Hal Westberg and Brian Lamb
                      An air quality monitoring program
                     was conducted in the Atlanta region
                     during Jury, 1981. This field study in-
                     cluded  data collection  at several
                     ground  stations as well  as airborne
                     measurements using an instrumented
                     aircraft.  Measurements  included
                     ozone,  oxides  of  nitrogen  (NOX).
                     peroxyacetyl nitrate (PAN),  individual
                     hydrocarbons (C, to C10), halocarbons,
                     condensation nuclei,  and  visual
                     distance plus numerous meteorologi-
                     cal parameters.  Isoprene and mono-
                     terpene  emission  rates  were de-
                     termined for the  most abundant na-
                     tural vegetation species in the Atlanta
                     region. Three tracer (SF,) experiments
                     were performed  in  order to better
                     understand dispersion patterns in the
                     Atlanta  area. Specific  objectives of
                     this research were (1) to quantify oxi-
                     dant transport and  production in the
                     Atlanta  plume; (2) to characterize an-
                     thropogenic and  biogenic ambient
                     hydrocarbon (HC) concentrations; and
                     (3)  to determine  the contribution of
                     natural hydrocarbon emissions to oxi-
                     dant production in the Atlanta area.
                      A well-defined pollutant plume was
                     observed  downwind of  Atlanta on
                     most afternoons  during the study
                     period. Ozone levels in the 130 to 160
                     ppb range were commonly observed
                     at distances of 35 to 45 miles from the
                     urban core. Elevated b,cat values were
                     also observed in  the Atlanta plume.
                     Nonmethane HC concentrations rang-
                     ing  from 113  to 1677  ppbC  were
                     recorded at Atlanta sampling  sites
                     during the 6 to 9 a.m. time period. A
                     mean concentration of 491 ppbC was
                     calculated from  about  50  samples.
                     Mean NOX concentrations varied from
                     44 to 68 ppb at three urban monitoring
sites. A mean HC/NOX ratio of 8.6 was
observed during the 6 to 9 a.m. period
in Atlanta. Biogenic HC including
isoprene,   a-pinene,    0-pinene,
A'-carene and myrcene were routinely
detected in air samples collected dur-
ing the 6 to 9 a.m. period. The natural
HC burden in these samples varied
from 2 to 7% at four sampling sites in
the Atlanta area.
  Ozone concentrations predicted by
city-specific Empirical Kinetic Model-
ing Approach (EKMA) Ozone Isopleth
Plotting Package,  (OZIPP) agreed
reasonably well  with observed  con-
centrations. This modeling effort con-
sisted  of assigning measured precur-
sor and meteorological parameters to
the 8 a.m.  Atlanta  air  parcel,
documenting the air parcel trajectory,
and comparing ozone concentrations
measured in the air parcel later in the
day with  model  predictions.  The
OZIPP ozone  concentrations  were
generally  about  10%  below the
observed levels.
  The  trajectory  analysis  used to
assign locations to the predicted max-
imum   ozone   concentrations   was
tested against the  results of the SF,
tracer experiments. At distances out
to 45 miles, the calculated trajectories
and the paths of  the  tracer plume
were in good agreement.
  An analysis of a recent HC and NOX
anthropogenic  emissions inventory for
the Atlanta area  indicated that the
HC/NO* ratio calculated  from the
emissions  data  was 1.5  while the
mean  ratio observed  in  ambient
samples was 8.6. Application of a sim-
ple box  model using the emissions
data yielded good agreement between
predicted and  observed NOX concen-

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nations,  but  the  predicted  an-
thropogenic  HC   concentration (99
ppbC) was approximately five times
less than the mean observed  concen-
tration (491 ppbC). These results sug-
gest that the anthropogenic HC emis-
sion  inventory  may  be severely
underestimated.
  An emission  inventory of blogenic
HC developed from a series of vegeta-
tion enclosure samples  collected dur-
ing  the  study  yielded  area-wide
average  fluxes  of  2500  ng/m2 h for
isoprene and  90 fig/m2 h for a-pinene.
These levels  are  similar to  those
reported  for  other  areas In the U.S.
Applications of the box model using
these rates provided an  upper bound
on the observed biogenic HC concen-
trations.   On  a  3.2-  x  3.2-km  (2-  x
2-mi) grid  average  basis, the  max-
imum    gridded    anthropogenic
hydrocarbon was 26,600 ^g/m2 h. The
97-  x  97-km  (60-  x  60-mi)  area
average   emission   flux   of  an-
thropogenic  HC was 1360 jtg/m2 h.
  This Project  Summary  was  devel-
oped by EPA's Atmospheric Sciences
Research  Laboratory,   Research
Triangle  Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same  title (see Project Report
ordering information at back).

Introduction
  It has become  apparent in recent years
that  photochemical smog problems exist
in  many  sections of the  United States.
Ambient ozone concentrations commonly
exceed the National Ambient Air Quality
Standard  (NAAQS) around the major ur-
ban  centers  in  California,  Texas,  and
throughout much of the midwestern and
eastern United States.  Oxidant  levels  in
excess of the standard  are  recorded  in
rural as well as urban regions of the coun-
try. Many studies have been undertaken
to  determine  the source(s)  of the high
ozone concentrations in these urban and
rural areas. The production of oxidants  in
urban plumes  and  subsequent transport
into  rural  regions   is   now  well
documented. However, considerable con-
troversy   still   exists   regarding
photochemical  ozone  production  from
naturally emitted  hydrocarbons.  In  many
cases,  natural  hydrocarbon  emission
estimates appear  to be comparable to an-
thropogenic hydrocarbon emission inven-
tories. However, the direct  comparison  of
natural and anthropogenic emission inven-
tories is probably not a valid method for
apportioning ozone contributions.  Uncer-
tainties  in  anthropogenic   hydrocarbon
emission  inventories  and in  the fate  of
naturally emitted organics make it difficult
to predict the  impact that each of these
categories will  have  upon  the develop-
ment of oxidants in a particular region.
  In order to improve our knowledge  of
the factors governing oxidant production
and transport in different regions of the
United States, a comprehensive air quality
monitoring program was  conducted in the
Southeast during the summer  of 1981.
The  Atlanta,  GA area  was  selected  for
study because it provided a large, isolated
city  surrounded by  natural  vegetation.
Specific goals of the  research program  in-
cluded:   (1)   measurement  of  an-
thropogenic  ozone precursor concentra-
tions in  Atlanta,  (2) development of a
natural hydrocarbon  emissions  inventory
for a 100-by-100-km area around Atlanta,
(3) documentation of  ozone production in
and around Atlanta, and  (4) acquisition  of
a meteorological data base sufficient for
air quality modeling.  All  of these objec-
tives were  achieved, although  the data
base is somewhat limited in that the field
study spanned  only three  weeks. Air
quality  data were collected between July
13 and August 3,  1981. The purpose  of
this report is to provide  a tabulation and
discussion of the data collected during the
study period.


Procedure
  The data collection phase of this pro-
gram consisted  of a joint effort involving
research  teams from Washington State
University and  the Environmental  Protec-
tion Agency   (Atmospheric   Sciences
Research  Laboratory, Research  Triangle
Park). Two special field study laboratories
and an instrumented aircraft were used  to
obtain air quality information in the Atlan-
ta region. Parameters that were measured
include ozone, oxides of nitrogen (NOJ,
halocarbons, Peroxyacetyl Nitrate  (PAN),
individual HC in  the  C2  to C,0 molecular
weight range, and numerous  meteorologi-
cal  parameters. Additional air quality  in-
formation was obtained  from  existing
monitoring stations operated  by federal,
state, and local agencies. Figure 1 shows
the location  of  surface stations and lists
the pollutants that were measured at each
site.
  Aircraft sampling  missions were con-
ducted  on  14 days during the  study
period. Two flights were flown on most
of the  14 days. An  early morning flight
was designed to establish boundary con-
ditions on  the upwind  side  of Atlanta.
The  morning  mixing  height  as  well  as
ozone  and  oxidant  precursor  transport
aloft were monitored during  the  morning
flight. Afternoon flights were conducted
in  the region downwind  of Atlanta  to
establish  dimensions  of the  urban plume
and  to  locate  the  region  of maximum
ozone buildup.

Results and Discussion
  Specific components of  the  intensive
monitoring program conducted in Atlanta
during July,  1981,  included measurement
of  ozone  precursor  concentrations  in
Atlanta, chemical characterization of the
upwind air flow, and monitoring of oxi-
dant production and  transport downwind
of Atlanta. The results of this sampling ef-
fort were used for  evaluation of  the city-
specific  Empirical  Kinetic  Modeling Ap-
proach  (EKMA) model Ozone  Isopleth
Plotting  Package  (OZIPP).   Trajectories
calculated from wind observations during
the study were used  to locate  predicted
maximum concentrations, and several SFe
urban tracer  releases  were  performed  to
aid  in the analysis of pollutant  transport
originating in Atlanta. This work also in-
cluded the documentation of available an-
thropogenic  HC and NOX  emission inven-
tories and  the  estimation   of  a similar
biogenic  HC  emission inventory based
upon series  of  vegetation enclosure
samples collected during the field study.
The  various  tasks  directly  related to the
investigation of ozone formation were ac-
complished through the operation of  an
instrumented  aircraft during 14 days along
with the  use  of two special field  monitor-
ing  laboratories  and several  existing  air
quality monitoring  sites during a total of
22 sampling days.

Oxidant Precursors
  Early  morning   (6  to  9   a.m.)  total
nonmethane  hydrocarbon  (NMHC)  con-
centrations  were  obtained  from   gas
chromatographic analyses  of  individual
species.  The  average  concentrations
varied between 113 and 1677 ppbC with a
mean equal  to  491  ppbC  at  four ur-
ban/suburban sites.  These  values  are
somewhat   low  compared   to  similar
measurements from  a number  of other
U.S. cities. The mean distribution of HC
was  approximately 55%   paraffin,  15%
olefin,  and  30%  aromatic,   but  this
distribution varied widely from day to day.
  Biogenic HC were routinely detected in
the early morning samples at the DeKalb
CC  site  and on  most days at Georgia
Tech  and  DeKalb-Peachtree. These  in-
cluded  isoprene,  a-pinene,  0-pinene,

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                                             Dekalb-Peachtree
                                                    HC, PAN, NO* Halocarbon, 03
                                         Georgia Tech  HC, PAN, NOX, 03

                                         Fulton Co. Health  HC, NO,
                                               • South Dekalb C. C.
        Chattahoochee River
Figure 1.    Location of ground level sampling sites in Atlanta.
A3-carene,  and  myrcene. The total
biogenic  contribution  to  ambient NMHC
varied from 2% to 7%. Isoprene typically
constituted 1% of the total NMHC.
  Average   concentrations   of  NOX
measured during  the 6 to 9 a.m. period
ranged from 10 to 200 ppb, and the mean
NOX concentrations measured at four sites
were  between  44  and  68  ppb.  Mean
HC/NOX  ratios at these sites were similar
with a mean  of 8.6, which is quite com-
parable to ratios observed in other urban
areas.

Oxidant Production and
Transport
  The NAAQS for ozone of  120 ppb was
exceeded on 3 different days at a site 24
miles downwind of urban  Atlanta, and the
standard was  exceeded at urban sites dur-
ing one  of  those days.  The maximum
hourly  average  ozone concentration was
172 ppb  observed in  the urban  center.
Daily  maximum  hourly  average ozone
concentrations were less  than 60 ppb  on
seven days, in the range 80 to 110 ppb on
fourteen days, and greater than  150 ppb
on  one  day.  Maximum  hourly average
concentrations of  PAN closely tracked the
ozone levels and  varied from less than 1
ppb to 4 ppb.
  During  most  of  the  flight  days,
moderate winds from  the northwest pro-
duced a well-defined, broad ozone plume
downwind  of  Atlanta  by midafternoon.
Ozone  levels in the 130 to 160 ppb range
were   commonly  observed   within  the
mixed  layer 35 to 45  mi  from the urban
core. These concentrations were generally
50 to 70 ppb above background concen-
trations.
  Stagnant wind conditions produced by
a stationary front over Atlanta created the
worst-case  ozone  formation  of  all  the
study  days.   Winds  were   light   and
variable,  and  the vertical mixing height
was limited to approximately 925 m during
the day.  Unlike the days  with  northwest-
erly  winds,  maximum  ozone  concentra-
tions were observed in the city at the  sur-
face and aloft. The maximum ozone con-
centration recorded with  the aircraft  was
approximately  190  ppb on July  24.  The
hourly  average maximum at  the  surface
on that day was 172 ppb. Outside of ur-
ban  Atlanta, the maximum surface con-
centration was 120 ppb.

EKMA  Evaluation
  Ozone production during the two types
of wind  conditions was  modeled using
city-specific EKMA with the  OZIPP com-
puter code. Model  input  data were taken
from surface and  aircraft measurements
during   each  modeled   day.  Maximum
ozone   concentrations   predicted  with
OZIPP  were approximately 10% less than
those observed. In addition,  a simple air
trajectory  analysis based  upon available
surface and upper-air data indicated that
the  predicted  ozone  maxima  occurred
very near  the locations and  times where
ozone  maxima were actually observed.
Results from three SFe tracer tests also in-
dicated that predicted trajectories correct-
ly  simulated   gas  transport  paths
originating in Atlanta and extending as far
as 45 mi downwind.


Precursor Emission Inventories
  Anthropogenic  HC and  NOX emissions
in Atlanta,  recently inventoried by  the
State of Georgia, are predominantly from
mobile sources. Annual average emission
rates from all sources for a 97-  x 97-km
(60-  x 60-mi) area  centered  over Atlanta
are 133,000  tons HC/day  and  275,000
tons  NOx/day.  These values  yield  an
HC/NOX  ratio equal to 1.5/1, assuming
average molecular weights of HC and NOX
to be 14.5 and 46 g/m respectively. This
ratio is significantly  less than observed in
the ambient  concentrations.  Application
of a simple box model  of the urban area
predicted an NOX  concentration essentially
equal to the mean observed  NOX concen-
tration.  However, predicted  HC concen-
trations for the same conditions were  5.0
times less than the mean  observed con-
centration.  The  results suggest that the
discrepancy in  the  HC/NOX  ratio is   the
result of severe  underestimation  of  an-
thropogenic HC emission rates.
  Biogenic HC emission  rates from   the
predominate tree  species in  Atlanta were
measured  using a branch  enclosure
technique.  Results from 20 samples were
similar in  magnitude  and  temperature
response  to  measurements conducted
elsewhere  in  the  U.S.  At 27°C,  the
isoprene  emission  rate  from  several
deciduous  species was 11 /ig/g/h, and
the a-pinene emission  rate  from loblolly
pine was  0.7  /xg/g/h.  These rates were
combined  with biomass density factors to
yield  emission  flux  estimates  for
deciduous and coniferous forests. In turn,
land-use distributions for Atlanta obtained
from  an  EPA analysis of Landsat  data
were  used with the estimated fluxes to
estimate the daily average emission rate: •
330 tons/day for isoprene and  24 tons/
day for a-pinene. On a unit area  basis,
these rates become  2500 jtg/m2 h and 90
/tg/m2 h,  respectively. For  comparison,
the average (3.2- x  3.2-km  grid) flux of
anthropogenic HC for  the 97-  x  97-km
area was  1350 /ig/m2 h and the highest
gridded  flux  of anthropogenic  HC was
26,600 /*g/m2 h.  Unlike the results for the
anthropogenic  emissions,  biogenic   HC

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  concentrations  predicted with  the  box
  model  represented  an upper • bound  on
  typical  measured levels.
         Hal Westberg and Brian Lamb are with Washington State University, Pullman,
           WA 99164-2730.
         William Lonneman is the EPA Project Officer (see below).
         The complete report, entitled "Ozone Production and Transport in the Atlanta,
           Georgia Region," (Order No. PB 85-173 839/AS; Cost:  $20.50, subject to
           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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