Energy and Power En gineering, 2010, 2, 190-195
doi:10.4236/epe.2010.23028 Published Online August 2010 (http://www.SciRP.org/journal/epe)
Simulation on SO2 and NOX Emission from Coal–Fired
Power Plants in North-Eastern North America
Shuangchen Ma
School of Environme nt al Sci ence and Engineering , North China Electric Power University , Baoding, China
Received April 9, 2010; revised May 17, 2010; accepted June 23, 2010
Abstract
MM5-SMOKE-CMAQ regional air quality modeling system was used to simulate pollutants emission from
coal–fired power plants in North-Eastern North America. The effects of SO2 and NOX on air quality produc-
ing from coal-fired power plants in the summer of 2001 were analyzed. Simulations show the contributions
of SO2 and NOX emission from coal-fired power plants using different scenarios, coal-fired power plants
from US and Canada contribute 67.2% and 32.8% for total SO2 concentration, 17.6% and 6.0% for total NOX
concentration in researched domain. Some control measures for coal-fired power plants were discussed.
Further controls for the emissions of SO2 and NOX from coal-fired power plants are necessary to reduce the
adverse environmental effects.
Keywords: Electric Generating units, CMAQ, Air Quality, Pollutants Control
1. Introduction
There is a long history of public concern about the emis-
sion of SO2 and NOX, these emissions contribute to acid
deposition, ultimately leading to a wide range of envi-
ronmental impacts, including damage to forests and soils,
fish and other living things, materials, and human health.
as well as the formation of fine particles and gases that
can impair visibility. SO2 and NOX all are the precursors
of acid rain [1]. Coal-fired power plants are regarded
globally as the major con tributor to local air quality deg-
radation and to global environmental impacts such as
acid rain and greenhouse phenomenon [2]. In the United
States, over 70 percent of this electricity was produced
through the combustion of fossil fuels, primarily coal and
natural gas, while 26 percent of this generation was pro-
duced from fossil fuels in Canada.
Legislation enacted for control the emission of these
two pollutants during the past two decades. In the Clean
Air Act Amendments (CAAA) of 1990, US Environ-
mental Protection Agency (EPA) has promulgated seve-
ral regulations and proposed rules to decrease these ad-
verse effects by reducing the emissions of SO2 and NOX
from coal-fired power plants. Since Congress passed the
Clean Air Act (CAA), power plants have cut emissions
of SO2 and NOX dramatically [3,4]. Many of these re-
ductions have been achieved by conversion to lower-
sulfur fossil fuels, primarily natural gas, with attendant
increases in costs. An alternative to conversion is to use
mitigation technologies to reduce the emissions. The
most common such technologies are reducing fuel sulfur
levels and filtering emissions using flue gas desulfuriza-
tion (FGD) and denitrification systems [5,6].
Analyses of the environmental effects arising from
power plants using a variety of models [7-10] suggest
that air quality effects depend on a wide variety of local
atmospheric parameters as well as on the combustion
technology. In some cases [11], regional transport domi-
nates local sources during pollution episodes, while in
other cases [12], transport is strongly affects by local
topology. In view of this variable sensitivity, the effects
of thermal power generation on air quality should be
assessed on a case by case basis for well defined geo-
graphical locations and time periods. Plumes from power
plants in certain locations have been implicated in sig-
nificantly reduced air quality [13,14].
In this study, we use regional atmospheric modeling to
explore the air quality implications of coal-fired power
plants in North-Eastern North America. We design dif-
ferent scenarios to study the contributions of coal-fired
power plants from United States and Canada. The con-
cerned pollutants are SO2 and NOX, which all are the
leading precursors of acid rain; they have large environ-
mental influences on the acid sensitive region s of North-
Eastern North America. Research results can be made
references for pursuing further emission reductions in US
and Canada.

S. C. MA
191
2. Modeling Description
EPA’s Models-3/Community Multi-scale Air Quality (C-
MAQ) [15] modeling system is a numerical transport and
chemical model which is developed by US EPA and is
implemented in a full modular approach. It means that
the user can select different chemical schemes (CBM-IV,
V, SAPRAC-99, RADM, etc.) and different numerical
schemes. It has different capabilities such as: Process
analysis, IRR analysis, etc.). It can handle interactions at
different dynamic scales and among multi-pollutants
with one modeling system. In this research, CMAQ (v4.5)
is employed to simulate SO2 and NOX for the summer
season of 2001 (May 1 throu gh Sep tember 1). Th e model
uses the Carbon Bond 4 (CB4) gas phase chemical me-
chanism with 2005 updates to extend the inorganic reac-
tions [16] .
2001 national emissions inventories was used and pro-
cessed by the Sparse Matrix Operator Kernel Emissions
Modeling System (SMOKE, v2.2) [17]. SMOKE system
provides an efficient tool for converting emissions in-
ventory data into the formatted emissions files: gridded,
temporalized and speciated, which are required by CM-
AQ. Area sources, non-road sources, mobile emissions,
biogenic emissions and point sources are treated sepa-
rately and merged.
Meteorological input data for the modeling runs are
processed using the National Center for Atmospheric Re-
search (NCAR) 5th generation Mesoscale Model (MM5,
v3.0) [18,19].Important MM5 parameterizations and
physics options apply to each summer include mixed
phase microphysics, planetary boundary layer (PBL),
and the land surface module. Meteorology-Chemistry
Interface Processor (MCIP, v2.0) is used to process the
MM5 output fields and generate the meteorological pa-
rameter fields required by SMOKE and CMAQ as well
as the dry deposition velocity fields of chemical species
required by CMAQ.
The model, as applied here, uses a horizontal resolute-
ion of 36 × 36 km2, with 23 layers in the vertical. The
model domain covers most Eastern of America in order
to minimize the effects of boundary co nditions on model
results. Additional model simulation was performed over
an embedded domain covering the North-Eastern North
America including the Great Lakes, with a grid spacing
of 12 km. Modeling coarse domain and 2-way nested
12km domain are shown in Figure 1.
We explore the effects of the three emission scenarios
described below:
1) Scenario 1 (Base case): All emissions in the 2001
criteria inventories were used.
2) Scenario 2: Coal emissions from power plants of
US and Mexico removed from point source inventory,
but kept the emission inventory of Canada same as Sce-
nario 1.
3) Scenario 3: Coal emissions from power plants in
Canada were removed from point source inventory, but
kept the emission inventories of US and Mexico same as
Scenario 1.
3. Modeling Evaluation
To validate the basic calculation, we compared the val-
ues of SO2 and NOX produced by the model for the time
period from May 1 to September 1, 2001 with the corre-
sponding measurements from AQS air quality monitor-
ing stations located in Doma in 2.
The simulation for SO2 and NOX aren’t very good,
the model has an under-prediction for SO2 and NOX ave-
rage concentration; Normalized Mean Bias (NMB) and
Normalized Mean Error (NME) for SO2 are –51.75%
and 71.28%; for NOX are –9.77% and 55.38% respec-
tively. The reason that modeled deviates from observa-
tions is that measurements are made near the sources
where the model emission schemes will never be able to
reproduce small-scale fluctuations observed. Sub-grid
scale variability in emissions will have a major impact
on the comparison between the model and observation.
More efforts should be done to improve the simulation
for SO2 and NOX. Moreover, the study’s conclusions
are obtained mainly by subtracting the scenarios from
base case, thereby reducing the effects of errors in re-
search results.
4. Modeling Results and Analysis
4.1. SO2 Emission and Changes Resulting from
Different Scenarios
SO2 are formed from fuel containing sulfur (mainly coal
and oil) is burned at power plants and during metal sme lt-
Domain 1
Domain 2
110 w100 w90 w 80 w 70 w
50 N
40
N
80 N
50 N
40
N
80
N
100 w90 w 80 w
Figure 1. The set of air quality modeling domain.

S. C. MA
192
ing and other industrial processes. SO2 emissions from
power plants react with other chemicals in the atmos-
phere to form sulfate particles, an important contributor
to the fine particle mix that circulates with the air we
breathe.
Figure 2 and Figure 3 show the average SO2 emission
flux and SO2 concentration in North-Eastern North
America in the summer season of 2001. Th e aver age SO 2
emission flux was 0.021mol/s in whole domain in the
summer. Several regions such as Chicago, southern Ohio,
northern West Virginia and western Pennsylvania etc.
were responsible for a significant proportion of SO2 em-
issions. Many large coal-fired power plants encompasses
in Ohio River Valley, which is a well-known emission
source of precursors of acid rain in the North America.
Same as emission, these areas had higher SO2 average
concentration in this summer.
Figure 4 shows the average difference of SO2 concen-
tration from base case and Scenario 2, which produce by
Average SO2 emission flux in the summer of 2001
a = em ission.mai ndata. d2
96
1
1
1.000
0.900
0.800
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0.000
moles/s 102
Figure 2. Average SO2 emission flux in the summer season
of 2001 in North-Eastern North America.
Average SO 2 concentration in the summer of 2001
a = CCTM_2001 sulfurcon.d2
96
1
1
0.010
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0.000
ppmV 102
Figure 3. Spatially resolved hourly Average SO2 concentra-
tion in the summer season of 2001 in North-Eastern North
America.
the average of SO2 concentration simulating from base
case minus those of Scenario 2. The regions of high SO2
concentration are the areas affected by the SO2 emission
of coal-fired power plants apparently. The highest dif-
ference of SO2 concentration exists at the region of west
Pennsylvania abou t 0.012 ppmv, it is easy to see that the
Ohio River Valley is biggest source of SO2 from coal-
fired power plants in researched domain.
Figure 5 shows the average SO2 concentration simu-
lating from three scenarios in the summer of 2001. The
average SO2 concentration of base case in domain 2 is
0.001 ppm in this summer. Average SO2 concentration
getting from Scenarios 2 and 3 are 0.00033 and 0.000672
ppm, these mean coal-fired power plants from US and
Canada contribute 67.2% and 32.8% for total SO2 con-
centration in researched domain.
According to EPA report, power plants account for
69% o f total SO 2 emission in the US in 2001 [20]. So, this
is consistent with our research results for the most part.
Average S O
2
concentration
b
etween
b
ase case and scenario 2
a = CCT M_2 001base cas e .d2 , b = CCTM_ 2001s ce nar io 2. d2
96
1
1
0.012
0.011
0.010
0.008
0.007
0.006
0.005
0.004
0.002
0.001
0.000
ppmV 102
Figure 4. Spatially resolved hourly average difference of
SO2 concentration from base case and Scenario 2 in the su-
mmer season of 2001 in North-Eastern North America.
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
Scenario 1Scenario 2Scenario 3
SO
2
co n centration, p pmV
Figure 5. Average SO2 concentration simulating from dif-
ferent scenarios in the summer of 2001.

S. C. MA
193
4.2. SO2 Emission Control from Coal-Fired
Power Plants
To help reduce acid rain, EPA is implementing a pro-
gram to reduce releases of SO2 and other pollutants from
coal-fired power plants. The first phase began in 1995
for SO2 and targets the largest and highest emit ting pow-
er plants. The second phase (started in 2000) sets tighter
restrictions on smaller coal-, gas-, and oil-fired plants.
This program will reduce annual SO2 emissions by 10
million tons (almost half the 1980 level) between 1980
and 2010. The control of SO2 emissions is currently
achieved using an innovative strategy called cap and
trade, established by the CAAA of 1990 and adminis-
tered by EPA, which is the world’s first large-scale cap-
and-trade program for air pollution. The program is de-
signed to reduce electric power sector emissions of SO2
through a national, market-based cap-and-trade system
for SO2 emissions with the goal of reducing the adverse
effe ct s of acid rain. The total SO2 release allowed is set at
a maximum of 8.95 million tons by the year 2010—ap-
proximately half of 1980 emissions [21].
Four main technology strategies for SO2 emissions
control have b een used by the electricity industry [22]:
1) Tall gas stacks that disperse emissions away from
immediate areas;
2) Intermittent controls which involve routine opera-
tional adjustments to reduce power plant SO2 emissions
in response to atmospheric conditions;
3) Pre-combustion reduction of sulfur from fuels; and
4) Removal of SO2 from the post-combustion gas
stream, the main method is FGD. There are a wide vari-
ety of FGD techniques, of which the most common are
wet scrubbers. Wet scrubbers work by using a slurry or
solution to absorb SO2, producing an initially wet by-
product. Frequently, limestone is used as the absorbent,
generating gypsum as a by-product. Typically, FGD can
achieve SO2 removal efficiency more than 90%.
4.3. NOX Emission and Changes Resulting from
Different Scenarios
NOX is the term used to describe the sum of nitric oxide
(NO), nitrogen dioxide (NO2), and other oxides of nitro-
gen. NOX plays a major role in the formation of acid rain,
secondary PM, ground level ozone, and smog in the atm-
osphere through a complex series of reactions with vola-
tile organic compounds (VOCs), sunlight and water va-
pors. The Relationship between VOC and NOX and O3
has extensive studies [23-26]. NOX also contributes to
visibility impairment. The major sources of human-pro-
duced NOX emissions are high-temperature combustion
processes such as those that occur in electrical power
plants and automobiles. Anthropogenic NOx emissions
in the US are estimated to total 22.2 Tg (as NO2) per year,
with 53% from transportation, coal-fired plants are an-
other major sources of NOX because of the fuel they burn
[27].
Figure 6 and Figure 7 show the average NOX emiss-
ion flux and concentration in North-Eastern North Am-
erica in summer season of 2001. The average NOX emis-
sion flux was 0.20 mol/s in whole domain in the su mmer.
Big cities such as Chicago, Detroit, and Toronto etc.
have much more emission of NOX than other areas, wh-
ich arising from local motor vehicle emission s primarily.
The biggest average NOx concentration is 0.056 ppmv in
Toronto city.
Figure 8 shows the average NOX concentration simu-
lating from three scenarios in the summer of 2001. The
average NOX concentration of base case in domain 2 is
0.00199 ppm in this summer. Average NOX concentra-
tion getting from Scenario 2 in Toronto city change to
0.029 ppmv, this mean the emissions of coal-fired power
plants from US can transport long distance through the
Average NO
X
emission flux in the summer of 2001
a = emission.maindata.d2
96
1
1
8.000
7.200
6.400
5.600
4.800
4.000
3.200
2.400
1.600
0.800
0.000
moles/s 102
Figure 6. Average NOX emission flux in summer season of
2001 in North-Eastern North America.
Average NO
X
concentration in the summer of 2001
a = CCTM_20 01NO
X
.d2
96
1
1
0.056
0.045
0.034
0.022
0.011
0.000
ppmV 102
Figure 7. Average NOX concentration in summer season of
2001 in North-Eastern North America.

S. C. MA
194
0
0.0005
0.001
0.0015
0.002
0.0025
Scenario 1Scenario 2Scenario 3
NO
X
concent rat ion, ppmV
Figure 8. Average NOX concentration simulating from dif-
ferent scenarios in the summer of 2001.
atmosphere to have obvious effect on Toronto. Average
NOX concentratio n getting from Scenario 2 and Scenario
3 is 0.00164 ppmv and 0.00187 ppmv. So, we can get
coal-fired power plants from US and Canada contributing
17.6% and 6.0% for NOX concentration in researched
domain. This is lower with same EPA research results
[20], coal-fired power plants contributed about 22% of
all U.S. NOX emissions in 2002, and this may be the
cause of under-prediction of model for NOX and the dif-
ferent object domain.
4.4. NOX Emission Control from Coal-Fired
Power Plants
In the past few years, EPA has promulgated several rules
to reduce NOX emissions, new rules for stationary sour-
ces (the Clean Air Interstate Rule, the Clean Air Mercury
Rule, and the Clean Air Visibility Rule), as well as State
plans to attain the National Ambient Air Quality Stan-
dard (NAAQS) of fine particle and ozone, will also sig-
nificantly reduce future NOX emissions. Beginning with
the CAAA of 1990, existing generators also have faced
increasingly stringent regulation of their nitrogen oxide
(NOX) emissions. Restrictions on summer emissions of
NOX from electricity generators in a majority of eastern
states are expected to become even tighter during the next
decade with the implementation of the call for amend-
ments to state implementation plans (SIPs) from the US
EPA, known as the NOX SIP Call. This new regulation is
designed to address the long-range transport of NOX as a
contributing factor to summer air pollution in cities on
the East Coast. Recent lawsuits filed by EPA and New
York State also have raised the possibility that many
existing generating sources were negligent in not bring-
ing their facilities into compliance with New Source
Performance Standard (NSPS) when they made substan-
tial investments enabling greater electricity generation at
these facilities [28].
Reduction of NOX emissions from industrial combus-
tion sources, especially coal-fired power plants is an im-
portant consideration in efforts undertaken to address the
NOX environmental concerns. New regulations announ-
ced by the US EPA facilitate utilities to develop new,
efficient, and robust post-combustion NOX control tech-
nologies [29]. The popular primary control technologies
in use in the United States are low-NOX burners (LNB)
and over-fire air. The average NOX reductions for spe-
cific primary controls have ranged from 35% to 63%
from 1995 emissions levels. The secondary NOX control
technologies applied on U.S. coal-fired utility boilers
include re-burning, selective catalytic reduction (SCR)
and selective non-catalytic reduction (SNCR) [30].
5. Conclusions
In this study, we use a regional atmospheric modeling
system-CMAQ to compute the air quality effects of coal-
fired power plants in North-Eastern North America. For
the time period from May 1 to September 1, 2001, we
consider three different scenarios to study the effects of
SO2 and NOX emission from coal-fired power plants. the
contributions of the coal plants for SO2 and NOX are
found to be big, coal-fired power plants from US and
Canada contribute 67.2% and 32.8% for SO2 concentra-
tion, 17.6% and 6.0% for NOX concentration in re-
searched domain. The use of existing emission reduction
rules and technologies can diminish the contributions of
coal-fired power plants for total emission of SO2 and
NOX. Further control measures for the emissions of SO2
and NOX from coal-fired power plants are necessary to
reduce the negative environmental effects.
6. Acknowledgements
The authors would lik e to acknowledge necessary condi-
tions provided by Waterloo Centre for Atmospheric Sci-
ences, University of Waterloo. The work is sponsored by
SRF for ROCS, SEM.
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