SENSITIVITY OF ANNUAL PM2.5 IN ATLANTA TO SO2 EMISSION REDUCTIONS 

RESULTING FROM GEORGIA’S MULTIPOLLUTANT RULE [391-3-1-.02(2)(sss)]

GA EPD performed photochemical grid modeling to determine the sensitivity of PM2.5

concentrations in the Atlanta nonattainment area to reductions in SO2 emissions due to the 

installation and operation of scrubbers at three large coal-fired power plants in Georgia. The 

analysis was based off of the Visibility Improvement State and Tribal Association of the Southeast 

(VISTAS) modeling, using the emissions inventories for both 2002 and 2009, and CMAQ version 

4.5 with the CB-IV chemical mechanism. Full annual SO2 sensitivities were conducted by GA 

EPD, based on 2002 meteorology and 2009 emissions, using a 12-km modeling grid, covering the 

state of Georgia and parts of the neighboring states (boundary conditions were obtained from 

simulations using a larger domain).

Cases Modeled

Sensitivities were modeled relative to 2009 emissions, to evaluate the efficiency of various control 

strategies to be implemented by 2009. Three large coal-fired power plants in Georgia were 

modeled to simulate actual expected reductions from the installation of scrubbers for SO2 removal 

(assuming a 95% control efficiency for SO2). Note that Plant Hammond Units 1-4, Plant Bowen 

Units 3-4, Plant Wansley Unit 1, and Plant Yates Unit 1 were not included in the analysis since they 

were required to already have scrubbers installed by December 31, 2008. The following is a detailed 

list of the three facilities that were modeled:

1. Scrubbers at Bowen: Installation of scrubbers on Plant Bowen Units 1-2 (average reduction 

of 218 tons-per-day of SO2 compared to pre-installation emissions; assuming a 95% control 

efficiency for SO2).

2. Scrubbers at Wansley: Installation of scrubbers on Plant Wansley Unit 2 (average 

reduction of 104 tons-per-day of SO2 compared to pre-installation emissions; assuming a 

95% control efficiency for SO2).

3. Scrubbers at Yates: Installation of scrubbers on Plant Yates Units 2-7 (average reduction of 

137 tons-per-day of SO2 compared to pre-installation emissions; assuming a 95% control 

efficiency for SO2).

Modeling Results

The results of the sensitivity analysis are reported in terms of the average reduction in annual PM2.5

in the 3x3 matrix centered around the grid-cell containing the monitoring site. Both absolute 

reductions (g/m3) and reductions normalized per ton-per-day of precursor controlled (ng/m3/TPD) 

are reported. Modeled reductions at each site were scaled relative to the observed speciated 5-year 

PM2.5 design value (weighted for 2000-2004), following the approach recommended in the EPA 

modeling guidance (EPA, Guidance on the Use of Models and Other Analyses for Demonstrating 

Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, EPA-454/B-07-002, April 

2007). Sensitivity analysis results for SO2 emission controls at Plant Wansley (Table 1), Plant 

Bowen (Table 2), and Plant Yates (Table 3) at monitors in Atlanta are summarized below. The 

monitor with the highest sensitivity in each Table is highlighted in bold red.
The “TPD reduction” value was calculated by taking the 2009 uncontrolled emissions (2009_TPD) 

used in the 2009 projection run and subtracting the 2009 controlled emissions (2009_TPD * 0.05) 

used in the 2009 sensitivity run. For Plant Wansley, the “TPD reduction” = 109.35 TPD 

uncontrolled - 5.47 TPD controlled = 103.88 TPD reduction. The “Annual Reduction in PM2.5 

(g/m3)” value was calculated by performing two 2009 photochemical grid modeling runs with 

2009 uncontrolled emissions (2009_TPD) and 2009 controlled emissions (2009_TPD * 0.05). The 

future design value for each 2009 model run was calculated by using the 2002 starting design value 

and applying a Relative Response Factor (RRF) as described in the EPA modeling guidance (EPA, 

Guidance on the Use of Models and Other Analyses for Demonstrating Attainment of Air Quality 

Goals for Ozone, PM2.5, and Regional Haze, EPA-454/B-07-002, April 2007). For more details, see 

“Section 6.1 Modeled Attainment Test” on pages 154-168 of “Georgia's State Implementation Plan 

for the Atlanta PM2.5 Nonattainment Area - May 24, 2010” (attached). The “Annual Reduction in 

PM2.5 (g/m3)” is equal to the difference between the 2009 future design value with 2009 

uncontrolled emissions (2009_TPD) and the 2009 future design value with 2009 controlled 

emissions (2009_TPD * 0.05). The “Normalized annual reduction in PM2.5 (ng/m3/TPD)” is 

calculated by dividing the “Annual Reduction in PM2.5 (g/m3)” by the “TPD reduction”. 

The Powder Springs-Macland Aquatic Center PM2.5 monitor (13-067-0004) did not start operating 

until February 5, 2003. As a result, this monitor was not included in the sensitivity analysis because 

it did not have a valid 5-year weighted 2002 design value (based on 2000-2004 data) since more 

than 2 years of data was missing. Without a valid 2002 design value, it is not possible to follow the 

EPA modeling guidance to calculate a 2009 future design value or the sensitivity impacts. Since 

2003, this monitor has measures annual PM2.5 concentrations below most of the other PM2.5 

monitors in Atlanta. Therefore, leaving it out of the analysis should not have any impact on the 

conclusions.

Table 1: Summary of sensitivity analysis results for SO2 emission controls at Plant Wansley.

Site Name

TPD 

reduction

Annual Reduction1

in PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)

Doraville (13-089-2001) 103.88 0.0858 0.826

E. Rivers School (13-121-0032) 103.88 0.0902 0.868

Fire Station No. 8 (13-121-0039) 103.88 0.0906 0.872

Forest Park-Georgia DOT (13-

063-0091)

103.88 0.0976 0.940

Gainesville-Fair Street School 

(13-139-0003)

103.88 0.0612 0.589

Gwinnett Tech (13-135-0002) 103.88 0.0714 0.687

Kennesaw-National Guard (13-

067-0003)

103.88 0.0839 0.807

South DeKalb (13-089-0002) 103.88 0.0928 0.893

Yorkville (13-223-0003) 103.88 0.0983 0.947

1

Scaled relative to the observed speciated 5-year PM2.5 concentrations (weighted for 2000-2004).
Table 2: Summary of sensitivity analysis results for SO2 emission controls at Plant Bowen.

Site Name

TPD 

reduction

Annual Reduction1

in PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)

Doraville (13-089-2001) 217.72 0.1682 0.772

E. Rivers School (13-121-0032) 217.72 0.1564 0.718

Fire Station No. 8 (13-121-0039) 217.72 0.1553 0.713

Forest Park-Georgia DOT (13-

063-0091)

217.72 0.1417 0.651

Gainesville-Fair Street School 

(13-139-0003)

217.72 0.1692 0.777

Gwinnett Tech (13-135-0002) 217.72 0.1717 0.788

Kennesaw-National Guard (13-

067-0003)

217.72 0.2117 0.973

South DeKalb (13-089-0002) 217.72 0.1411 0.648

Yorkville (13-223-0003) 217.72 0.1549 0.711

1

Scaled relative to the observed speciated 5-year PM2.5 concentrations (weighted for 2000-2004).

Table 3: Summary of sensitivity analysis results for SO2 emission controls at Plant Yates.

Site Name

TPD 

reduction

Annual Reduction1

in PM2.5 (g/m3)

Normalized annual 

reduction in PM2.5

(ng/m3/TPD)

Doraville (13-089-2001) 137.20 0.1530 1.115

E. Rivers School (13-121-0032) 137.20 0.1673 1.220

Fire Station No. 8 (13-121-0039) 137.20 0.1680 1.224

Forest Park-Georgia DOT (13-

063-0091)

137.20 0.1795 1.308

Gainesville-Fair Street School 

(13-139-0003)

137.20 0.0988 0.720

Gwinnett Tech (13-135-0002) 137.20 0.1207 0.880

Kennesaw-National Guard (13-

067-0003)

137.20 0.1589 1.158

South DeKalb (13-089-0002) 137.20 0.1641 1.196

Yorkville (13-223-0003) 137.20 0.1579 1.151

1

Scaled relative to the observed speciated 5-year PM2.5 concentrations (weighted for 2000-2004).

Clean Data Determination

On December 8, 2011, EPA promulgated its determination (76 FR 76620) that the Atlanta 

nonattainment area had attained the 1997 annual average PM2.5 National Ambient Air Quality

Standard (NAAQS). This determination was based upon quality-assured and certified ambient air 

monitoring data for the 2008-2010 period that showed design values below 15.0 μg/m3 as indicated 

in Table 4. 
Table 4. Annual and Three-year Average Ambient PM2.5 Concentrations.

*The Georgia Tech monitor stopped operation on December 29, 2008.

Discussion

The Atlanta PM2.5 nonattainment area redesignation request and maintenance plan accounted for 

controls from Georgia’s Multipollutant Rule [391-3-1-.02(2)(sss)]. This rule requires flue gas

desulfurization (FGD) and selective catalytic reduction (SCR) controls on the majority of coal-fired 

EGUs in Georgia. The required FGD control implementation date varies by EGU, starting on 

December 31, 2008. SO2 controls were operating for the entire year of 2010 as follows:

 Plant Hammond – controls on 4 of 4 units;

 Plant Bowen – controls on 3 of 4 units;

 Plant Wansley – controls on 2 of 2 units;

 Plant Yates – controls on 1 of 7 units.

Table 5 shows the annual SO2 emissions for Plant Hammond, Plant Bowen, and Plant Wansley for 

the period 2003 through 2010. Also, the table includes the electrical generation, SO2 emissions per 

106 MWh generation, the average SO2 emissions per 106 MWh generation for 2003-2007, the 

uncontrolled SO2 in 2008-2010 (assuming average SO2 emissions per 106 MWh generation for 

2003-2007 x generation in 2008, 2009, 2010), and the controlled SO2 in 2008-2010 (difference 

between uncontrolled and actual SO2 emissions).

In addition, Table 5 shows the annual SO2 emissions for Plant Yates (Unit 1) for the period 2008

through 2010. Also, the table includes the uncontrolled SO2 in 2008-2010 (SO2 emissions in 2008, 

2009, 2010 divided by 0.05), and the controlled SO2 in 2008-2010 (difference between uncontrolled 

and actual SO2 emissions).

Ambient PM2.5 Concentration (μg/m3)

Site Name 2003 2004 2005 2006 2007 2008 2009 2010 2008-2010 

w/out data 

substitution

2008-2010 

with data 

substitution

Forest Park-Georgia DOT 

(13-063-0091) 16.0 16.8 16.6 16.7 15.3 13.7 11.5 13.4 12.9 N/A

Kennesaw-National Guard 

(13-067-0003) 16.0 15.8 16.3 16.5 15.3 13.5 11.2 12.2 12.3 N/A

Powder Springs-Macland 

Aquatic Center (13-067-

0004)

15.2 15.2 15.5 15.8 14.5 13.1 10.3 12.1 11.9 12.3

South DeKalb (13-089-0002) 15.0 16.1 15.5 15.4 14.8 12.7 11.4 12.3 12.1 N/A

Doraville (13-089-2001) 15.4 15.5 15.8 14.5 15.1 13.1 11.7 12.2 12.3 N/A

E. Rivers School (13-121-

0032) 16.1 16.1 15.9 15.4 15.7 13.0 11.6 12.2 12.3 13.0

Fire Station No. 8 (13-121-

0039) 17.7 17.6 17.0 18.4 -- 7.6 12.1 14.5 11.4 13.6

Georgia Tech (13-121-0048)* -- -- -- 15.1 15.5 14.3 -- -- -- --

Gwinnett Tech (13-135-0002) 16.2 16.1 16.1 16.9 14.2 12.4 11.6 12.3 12.1 12.5

Gainesville-Fair Street 

School (13-139-0003) 14.7 14.0 14.5 13.8 13.4 11.8 10.2 11.4 11.2 11.9

Yorkville (13-223-0003) 13.8 13.4 14.6 13.9 14.3 11.9 9.9 11.2 11.0 11.6
The “AVG 08-10 Controlled” value in Table 5 is the amount of SO2 emission reductions that can be 

attributed to Georgia’s Multipollutant Rule [391-3-1-.02(2)(sss)] between 2008 and 2010. By

multiplying the controlled SO2 emissions for each facility by the normalized annual sensitivity in 

Tables 1 - 3 will quantify the impact of SO2 emission controls from each facility on annual PM2.5

concentrations. 

Table 5. Controlled SO2 emissions from Plant Hammond, Plant Bowen, Plant Wansley, and 

Plant Yates (Unit 1) in 2008 - 2010.

Facility 2003 2004 2005 2006 2007 2008* 2009* 2010*

Hammond SO2 (tpy) 35,900 37,700 39,500 40,600 47,800 12,500 900 2,427

generation 4.79 4.11 4.64 4.27 5.09 4.32 3.73 3.23

SO2/gen 7,494.8 9,172.7 8,512.9 9,508.2 9,391.0 2,893.5 241.3 751.4

AVG 03-07 8,815.9

Uncontrolled 38,084.8 32,883.4 28,475.4

Controlled 25,584.8 31,983.4 26,048.4

AVG 08-10 27,872.2

Bowen SO2 (tpy) 164,900 165,900 186,500 206,400 196,800 148,100 54,800 7,618

generation 21.9 21.9 23.3 23.7 24 23.4 22.9 24.7

SO2/gen 7,529.7 7,575.3 8,004.3 8,708.9 8,200.0 6,329.1 2,393.0 308.4

AVG 03-07 8,003.6

Uncontrolled 187,285.1 183,283.2 197,689.8

Controlled 39,185.1 128,483.2 190,071.8

AVG 08-10 119,246.7

Wansley** SO2 (tpy) 94,000 99,000 101,500 96200 93,900 74,300 7400 2,343

generation 13.7 14 15.1 14.8 16.1 15.5 11.8 9.8

SO2/gen 6,861.3 7,071.4 6,721.9 6,500.0 5,832.3 4,793.5 627.1 239.1

AVG 03-07 6,597.4

Uncontrolled 102,259.4 77,849.1 64,654.3

Controlled 27,959.4 70,449.1 62,311.3

AVG 08-10 53,573.3

Yates, Unit 1 SO2 (tpy) 352 175.9 286

Uncontrolled 7,040.0 3,518.0 5,726.0

Controlled 6,688.0 3,342.1 5,439.7

AVG 08-10 5,156.6

Source: EPA Clean Air Markets Division

* SO2 control, required by Georgia Rule (sss), was operational on one or more EGUs for partial or 

full year

** does not include emissions from facility’s gas-fired units
Figure 1. Map of Plant Hammond, Plant Bowen, and Plant Wansley relative to the ten Atlanta 

PM2.5 monitors.

The location of Plant Hammond, Plant Bowen, Plant Wansley and Plant Yates relative to the ten 

Atlanta PM2.5 monitors is shown in Figure 1. The Yorkville monitor (13-223-0003) has the highest 

normalized sensitivity to SO2 emissions from Plant Wansley when compared to all the other Atlanta 

monitors (see Table 1). Therefore, a conservative approach would be to use the SO2 normalized 

sensitivity at the Yorkville monitor for all the monitors in Atlanta.

The Kennesaw-National Guard monitor (13-067-0003) has the highest normalized sensitivity to SO2

emissions from Plant Bowen when compared to the other Atlanta monitors (see Table 2). 

Therefore, a conservative approach would be to use the SO2 normalized sensitivity at the 

Kennesaw-National Guard monitor for all the monitors in Atlanta.

Since we did not perform SO2 emission sensitivities from Plant Hammond and Plant Hammond is 

located farther away from all the Atlanta monitors when compared to Plant Bowen, a conservative 

approach would be to use the Plant Bowen SO2 normalized sensitivities from the KennesawNational Guard monitor to represent the impact from Plant Hammond at all the Atlanta monitors.
The Forest Park monitor (13-063-0091) has the highest normalized sensitivity to SO2 emissions 

from Plant Yates when compared to all the other Atlanta monitors (see Table 3). Therefore, a 

conservative approach would be to use the SO2 normalized sensitivity at the Forest Park monitor for 

all the monitors in Atlanta.

The maximum impact on annual PM2.5 concentrations at each Atlanta PM2.5 monitors due to SO2

emission reductions that can be attributed to Georgia’s Multipollutant Rule [391-3-1-.02(2)(sss)]

controls at Plant Bowen, Plant Hammond, Plant Wansley, and Plant Yates is calculated in Table 6. 

Table 6. Annual PM2.5 impact on Atlanta monitors from SO2 controls on Plant Hammond, 

Plant Bowen, Plant Wansley, and Plant Yates in 2008-2010.

Controlled 

Emissions 

(TPY)

Controlled 

Emissions 

(TPD)

Normalized 

Sensitivity

(ng/m3/TPD)

Annual PM2.5

Impact 

(g/m3)

Plant Bowen 119,246.70 326.70 0.973 0.318

Plant Hammond 27,872.21 76.36 0.973 0.074

Plant Wansley 53,573.25 146.78 0.947 0.139

Plant Yates 5,156.60 14.13 1.308 0.018

TOTAL 0.550

Table 7. Three-year Average Ambient PM2.5 Concentrations with/without data substitution 

and with/without Rule 391-3-1-.02(2)(sss). 

Ambient PM2.5 Concentration (μg/m3)

Site Name 2008-2010 without 

data substitution 

and with Rule 

391-3-1-.02(2)(sss)

2008-2010 with 

data substitution 

and with Rule 

391-3-1-.02(2)(sss)

2008-2010 without 

data substitution 

and without Rule 

391-3-1-.02(2)(sss)

2008-2010 with 

data substitution 

and without Rule 

391-3-1-.02(2)(sss)

Forest Park-Georgia DOT 

(13-063-0091) 12.9 N/A 13.5 N/A

Kennesaw-National Guard 

(13-067-0003) 12.3 N/A 12.9 N/A

Powder Springs-Macland 

Aquatic Center (13-067-

0004)

11.9 12.3 12.5 12.9

South DeKalb (13-089-0002) 12.1 N/A 12.7 N/A

Doraville (13-089-2001) 12.3 N/A 12.9 N/A

E. Rivers School (13-121-

0032) 12.3 13.0 12.9 13.6

Fire Station No. 8 (13-121-

0039) 11.4 13.6 12.0 14.2

Gwinnett Tech (13-135-0002) 12.1 12.5 12.7 13.1

Gainesville-Fair Street 

School (13-139-0003) 11.2 11.9 11.8 12.5

Yorkville (13-223-0003) 11.0 11.6 11.6 12.2
Conclusion

The total impact on the PM2.5 annual measurements at the ten Atlanta PM2.5 monitors from the 

application of SO2 controls from Georgia’s Multipollutant Rule [391-3-1-.02(2)(sss)] is 0.6 g/m3

(rounded up from 0.550 g/m3). By adding this value to the 2008-2010 annual PM2.5 design value 

results in revised 2008-2010 annual PM2.5 design values that are all well below the 1997 annual 

PM2.5 NAAQS of 15.0 g/m3(see Table 7). Therefore, removal of these controls would not have 

resulted in 2008-2010 annual PM2.5 design value over the 1997 annual PM2.5 NAAQS.