There is increasing recognition that controls on NO(x) emissions may be necessary, in addition to existing and future Volatile Organic Compounds (VOC) controls, for the abatement of ozone (O3) over portions of the United States. This study compares various combinations of anthropogenic NO(x) and VOC emission reductions through a series of model simulations. A total of 6 simulations were performed with the Regional Oxidant Model (ROM) for a 9-day period in July 1988. Each simulation reduced anthropogenic NO(x) and VOC emissions across-the-board by different amounts. Maximum O3 concentrations for the period were compared between the simulations. Comparison of the simulations suggests that: (1) NO(x) controls may be more effective than VOC controls in reducing peak O3 over most of the eastern United States; (2) VOC controls are most effective in urban areas having large sources of emissions; (3) NO(x) controls may increase O3 near large point sources; and (4) the benefit gained from increasing the amount of VOC controls may lessen as the amount of NO(x) control is increased. This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use

Chu, Shao-Hang

Roselle, Shawn J.

Schere, Kenneth L.

English

NASA Technical Reports Server

N95- 10611
ESTIMATES OF OZONE RESPONSE TO VARIOUS COMBINATIONS OF
NO x AND VOC EMISSION REDUCTIONS IN THE EASTERN UNITED STATES
Shawn J. Roselle,*t Kenneth L. Schere,*t and Shao-Hang Chu_;
*Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric
Administration, Research Triangle Park, North Carolina 27711 ; "tOn assignment to the Atmospheric Research
and Exposure Assessment Laboratory, U.S. Environmental Protection Agency; :l:Office of Air Quality Planning
& Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711
ABSTRACT
There is increasing recognition that controls on NO,
emissions may be necessary, in addition to existing and future
VOC controls, for the abatement of ozone (03) over portions of
the United States. This study compares various combinations of
anthropogenic NO_ and VOC emission reductions through a
series of model simulations. A total of 6 simulations were per-
formed with the Regional Oxidant Model (ROM) for a 9-day
period in July 1988. Each simulation reduced anthropogenic
NO_ and VOC emissions across-the-board by different amounts.
Maximum O3 concentrations for the period were compared
between the simulations. Comparison of the simulations
suggests that (I) NO_ controls may be more effective than VOC
controls in reducing peak O 3 over most of the eastern United
States; (2) VOC controls are most effective in urban areas
having large sources of emissions; (3) NO, controls may
increase 03 near large point sources; and (4) the benefit gained
from increasing the amount of VOC controls may lessen as the
amount of NO_ control is increased.
This paper has been reviewed in accordance with the U.S.
Environmental Protection Agency's peer and administrative
review policies and approved for presentation and publication.
Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
1. INTRODUCTION
Feasible solutions to the tropospheric ozone (03) problem
have evaded scientists and policy makers for many years.
Emissions which are precursors to O3 formation, volatile
organic compounds (VOC) and nitrogen oxides (NOx), have to
be controlled to reduce O_ concentrations. The relationship
between precursor controls and actual reductions in 03 concen-
trations is highly nonlinear. Historically, efforts to reduce O 3
concentrations have focused primarily on VOC emissions.
Recent modeling studies (Trainer et al., 1987; Sillman et al.,
1990; McKeen et al., 1991) have characterized much of the
eastern United States as NOx-limited, suggesting that NO_
controls may be more effective. However, certain areas such
as New York City may be VOC-limited (EPA, 199l), where
NO_ emission controls may be counter-productive in reducing
O3 concentrations in the local area. Selection of VOC or NO x
controls (or a combination of the two) will probably vary
spatially, depending on the chemical regime of the location.
Previous studies, such as EPA (1991), have examined combina-
tions of emission reductions and have provided valuable insight
into the effectiveness of different controls. However, scientific
understanding of the results of these studies has been hampered
because of the spatial variability in emission reductions. There
is a clear need for a systematic examination of NO_ and VOC
emission reductions to provide a basis for more effectively
formulating future control strategies.
This study examines the response of maximum ozone
concentrations to uniform spatial and temporal reductions in
VOC and NO, emissions. The Regional Oxidant Model (ROM)
(Lamb, 1983; Young et al., 1989) was used to simulate the
July 2-10, 1988 period of high O 3.
2. PROCEDURE
A total of twenty-five simulations are planned for this
study. Six have been completed, including simulations with the
following sets of anthropogenic emissions (the same set of bio-
genic emissions were used for each simulation): (1) Base case;
(2) 25% VOC and 25% NO, controls; (3) 75% VOC and 25%
NO, controls; (4) 50% VOC and 50% NO, controls; (5) 25%
VOC and 75% NO, controls; (6) 75% VOC and 75% NO,
controls. Simulations were performed with ROM version 2.2.
ROM simulates most of the physical and chemical processes re-
sponsible for the buildup of O3 on regional scales (- 10 _ km2).
Detailed descriptions of the model can be found in Lamb
(1983); Young et al. (1989); and Roselle et al. (1991). For this
study, the modeling domain was chosen to cover the eastern
United States, consisting of 16,128 grid cells within each verti-
cal layer. The grid size was (1/4) ° longitude x (1/6)* latitude,
or approximately (18.5 km) 2. The model uses 3 dynamic verti-
cal layers to represent the planetary boundary layer and capping
inversion. During an entire simulation period, horizontal advec-
tion, diffusion and gas-phase chemistry for specified pollutants
are modeled prognostically in the 3 vertical layers. Meteorolog-
ical fields are derived by objective analysis of observed data
from both surface and upper-air stations. The chemistry mecha-
nism incorporated in the model is the Carbon-Bond Mechanism
1V (Gery et al., 1989), which consists of 83 reactions and 33
individual species. In all simulations, relatively clean air
([O31 =- 30 ppb) was assumed for both the initial and lateral
boundary conditions. The O3 boundary condition for the top of
the model was -40 ppb. It should be noted that there are limita-
tions to the ROM, which include the inability to resolve sub-
89
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grid processes, uncertainties in the input data, crude treatment
of point sources, and relatively coarse horizontal and vertical re-
solution. Evaluations of the ROM (Schere and Wayland, 1989;
Pierce et al., 1990a; Roseile, 1992) have shown that the model
does well in positioning most of the major 03 plumes, but tends
to underpredict concentrations when observed values are above
70-80 ppb, and overpredict values below this level. For the
current simulation, the model underpredicted maximum 03 con-
centrations over the episode by 17 ppb (11%), on average.
Anthropogenic emissions were derived from the 1985
National Acid Precipitation Assessment Program (NAPAP) in-
ventory (Saeger et al., 1989), which included emissions of
VOC, NO,, and CO (carbon monoxide). Major point, area, and
mobile source emissions were considered in the inventory with
day of the week (Saturday, Sunday, and weekday) and hourly
variations on the emission rates. Additionally, mobile source
evaporative emissions were adjusted for daily temperature varia-
tions using the empirical model MOBILE4.2 (EPA, 1989). For
each emission reduction simulation, the emissions from all
anthropogenic sources were reduced uniformly in space and
time. Biogenic emissions were provided by the Biogenic
Emissions Inventory System (BEIS) of Pierce et al. (1990b).
Biogenic emissions were the same in each simulation.
3. DISCUSSION AND RESULTS
3.1 Base Case Simulation
Figure i a presents the maximum hourly-averaged predicted
03 concentrations for each grid in ROM's lowest vertical layer
(100-300 m deep) for the 9-day period July 2-10, 1988.
Maximum concentrations over the entire episode were chosen
for this analysis because of their importance in determining if a
location has exceeded the National Ambient Air Quality
Standard (NAAQS) for ozone. In this plot, lower concentra-
tions are denoted with lighter shades and higher concentrations
with darker shades. High concentrations of ozone (> 120 ppb)
were predicted over a large area in association with a stagnating
high pressure system. Anticyclonic circulation around the high
pressure system dominated the Great Lakes, Ohio Valley, and
mid-Atlantic States. The Northeast Corridor (the extended
overlapping urban areas from Washington, D.C. through
Boston), however, experienced flow from the southwest in
association with a low pressure trough along the East Coast.
High O3 concentrations extended from central Georgia to Lake
Huron, and from St. Louis, Missouri to the coast of Maine.
Much of this area was predicted to have O3 in excess of
120 ppb. Concentrations above 180 ppb were predicted near
Chicago, Lake Michigan, Lake Erie, Washington, D.C.,
Philadelphia, and New York City. Concentrations above
150 ppb were predicted for Atlanta, Lake Ontario, Pittsburgh,
Charleston (West Virginia), and along a small segment of the
Ohio River. The highest predicted hourly-average O3 concen-
tration was 262 ppb, which occurred over Lake Michigan. The
average peak O3 concentration across the domain was 75 ppb.
Predicted concentrations were relatively low (< 60 ppb) over
other areas, although smaller composite (over the episode) urban
plumes were apparent in Texas, Oklahoma, and Louisiana.
3.2 Comparison of Simulations
25% VOC. 25% NOx Reductions. Compared to the base
case (fig. lb), _ predicted O3 was reduced by 5%-15% across
most of the Eastern United States for this control strategy.
Ozone decreased by the largest amount (> 15%) in an area over
Lake Michigan, which had high concentrations in the base case.
To the north and south of this area, the model predicted an
increase (> 5 %) in O3 for this control strategy. Areas with an
increase in O3 were widely-scattered across the domain and
were primarily located near emission source regions. The
spatial extent of these areas was limited to just a few grid cells.
7_i% VOC. 25% NOx Reductions. Figure lc shows that
for this strategy, O3 was reduced by 15% to 30% in many areas
of the Northeast, the Great Lakes, and over Texas and Louisi-
ana. In composite urban plumes from New York City, Toronto,
Montreal, Detroit, Cleveland, Chicago, and Houston, O3
decreased by more than 30%. Other areas of the domain saw
O3 reductions on the order of 5%-15%. The largest reduction
in O3 was 56%, which occurred over Lake Michigan.
Comparing results from the simulations with 25 % VOC,
25 % NOx controls and 75 % VOC, 25 % NO, controls (fig. lb
and c) shows the relative benefit of adding more VOC controls
to a NO, control of 25 %. Increasing VOC controls had the
greatest impact on the Northeast, the Great Lakes area, and the
western Gulf Coast states, as evidenced by the large areas with
15%-30% reductions in 03. Additionally, with higher VOC
controls, there were fewer grid cells showing an increase in O3
over the base case simulation. Very little additional reduction
in 03 was predicted for the Southeast.
50% VOC. 50% NOx Reductions. In this simulation, O3
decreased by 15%-30% over most of the model domain
(fig. ld). Over Lake Michigan and scattered over the South-
east, O3 decreased by more than 30%. On average, peak O3
concentrations decreased by 17%. There were a few locations
with higher O3 concentrations following the emissions reduction;
the spatial extent of these regions was limited to only a few grid
cells, located near large NOx point sources.
In a similar modeling study, McKeen et al. (1991) also
examined O3 sensitivity to 50% reductions in both VOC and
NO x emissions. Their results are consistent with this study,
showing a decrease in afternoon ozone concentrations of 12%
to 16% across much of the eastern United States, but an
increase in some grid cells which had high NO, emissions.
25% VQC. 75% NOx Reductions. In this simulation, 03
was reduced by more than 30% across much of the domain (fig.
le). The controls reduced O3 by 29% on average. Ozone de-
creased by more than 50% across the Southeast. There were a
few grid cells near large NOx sources which had higher O3 in
this simulation than in the base case. Some of the specific
locations included Toronto, Chicago, Tampa, Houston, Baton
Rouge, and New Orleans. The locations with an increase in O3
were generally limited in spatial extent to the core urban area.
75% VOC. 75% NQx Reductions. This simulation
compares well to the simulation with 25 % VOC and 75 % NO_
controls. Ozone decreased substantially with the emission
reductions (fig. If); much of the East was predicted to have O3
reduced by more than 30%. The Southeast had the largest
reductions in 03, however, the spatial extent of the area with
> 50% decrease in O3 was smaller than in the simulation with
25% VOC and 75% NO, reductions. Additionally, there were
90
80-90
i 90-120
• 120 -150
• 150-180
I > =180
Percent
Dhlecence
l>s
-5to 5
-5 to -15
-15 to -30
-30to -50
< -50
Percent
Difference
1>5
-5to5
-5 to -15
-15 to -30
-30tO -50
< --50
Fig. 1. (a) Episode maximum hourly-average 03 (ppb) in layer 1 for the base case simulation. (b-f) Percent difference in episode
maximum 03 (layer I) between the base case and simulations with anthropogenic emission reductions of: (b) 25% VOC, 25%
NO,, (c) 75% VOC, 25% NO_, (d) 50% VOC, 50% NO_, (e) 25% VOC, 75% NO,, and (f) 75% VOC, 75% NO,.
91
fewer grid cells in this simulations-which had higher 03 than the
base case. The additional VOC controls examined in this
simulation further improved 03 in many of the major urban
plumes, but hindered improvements in the Southeast where large
NO, controls were highly effective.
policy makers with detailed information on the predicted
chemical nature of the eastern U.S. and may provide additional
guidance for developing control strategies.
REFERENCES
4. SUMMARY AND CONCLUSIONS
Simulations of the eastern United States were performed
with the ROM for 6 different levels of anthropogenic emissions.
The period of July 2-10, 1988 was studied because of the ex-
tremely high O_ concentrations that occurred over the area.
Initial results have been analyzed (summarized in Table 1) and
have provided preliminary indications of the effects of different
levels of emission controls. VOC controls benefit urban plumes
near their sources, including the cities of Chicago, Detroit,
Cleveland, Toronto, New York, Houston, and Dallas. NO,
controls produced widespread reductions in ozone. Controlling
NO_ by 75 % (with limited VOC control) made a much larger
impact than 75 % VOC control (with limited NO, control). Re-
ducing VOC emissions caused almost no increase in 03, where-
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States is NO_-Iimited, which is in agreement with modeling
studies by Sillman et al. (1990) and McKeen et al. (1991).
As in most modeling studies, there are uncertainties that
should be emphasized. In regards to scale, the ROM grid size
may be too coarse to adequately resolve the fast chemical reac-
tions which occur near large emission sources, and therefore the
accuracy is reduced in model estimates of near-urban increases
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Further analysis will be performed on these simulations,
and on the 19 simulations to be performed in the future. This
paper examined only maximum predicted O3 concentrations.
The final objectives in this study are to develop response
surfaces (isopleth plots) for various pollutants as a function of
VOC and NO, controls. Analysis of the response surfaces will
then be performed on chemically-coherent subregions of the
model domain. Upon completion, this research should provide
Table 1. Statistics on Episode Maximum Ozone*
Reduction Strategy
Mean Mean difference from
Cone. base case
(ppb) (ppb) (%)
Base Case 75
25 % NO, 25 % VOC 69 -6 -7
25% NO, 75% VOC 66 -9 -10
50% NO x 50% VOC 60 -15 -17
75 % NOx 25% VOC 49 -26 -29
75 % NO, 75 % VOC 49 -26 -29
* Computed for model layer 1 over the entire domain (N = 16,128 grid cells).
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Estimates of ozone response to various combinations of NO(x) and VOC emission reductions in the eastern United States

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