**SENSITIVITY OF A NNUA**  **L PM2.5 IN AT**  **LA NTA**  **TO SO**  **2 EMISSION**  **REDUCTIONS**

**RESULTING FROM GEORGIA** **’S MULTIPOLLU TA**  **NT RULE**  **[391 -** **3 -**  **1 -**  **.02(2)(sss)]** GA EPD performed photochemical grid modeling to determine the sensitivity of PM 2.5 concentrations in the Atlanta nonattainment area to reductions in SO 2 emissions due to the installation and operation of scrubbers at three large coal - fired power plants in Georgia. The anal ys is was based off of the Visibility Improvement State and Tribal Association of the Southeast (VI STAS) modeling, using the emissions inventories for both 2002 and 2009, and CMAQ version 4.5 with the CB - IV chemical mechanism. Full annual SO 2 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 strate gies 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 SO 2 removal (assuming a 95% control efficiency for SO 2 ) . 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 analys is 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 SO 2 compared to pre - installation emissions; assuming a 95% control efficiency for SO 2 ). **2. Scrubbers at Wansley**  : Installation of scrubbers on Plant Wansley Unit 2 (average reduction of 104 tons -per- day of SO 2 compared to pre - installation emissions; assuming a 95% control efficiency

for SO 2 ). **3. Scrubbers at Yates**  : Installation of scrubbers on Plant Yates Units 2 - 7 (average reduction of 137 tons -per- day

of SO 2 compared to pre - installation emissions; assuming a 95% control efficiency for SO 2 ). **Modeling Results**  The results of the sensitivity anal ys is are reported in terms of the average reduction in annual PM 2.5 in the 3x3 matrix centered around the grid- cell containing the monitoring site. Both absolute reductions ( g/m 3 ) and reductions normalized per ton-per- day of precursor controlled (ng/m 3 /TPD) are reported. Modeled reductions at each site were scaled relative to the observed speci ated 5 - ye ar PM 2.5 design value (weighted for 2000 - 2004), following the approach recommended in the EPA modeling guidance (EPA, Guidance on the Use of Models and Other Anal yses for Demonstrating Attainment of Air Quality Goals for Ozone, PM 2.5 , and Regional Haze, EPA - 454/B - 07 - 002, April 2007) . Sensitivity

anal ys is results for SO 2 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 sens itivity 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/m 3 ) ” 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 2 002 starting design value and appl ying a Relative Response Factor (RRF) as described in the EPA modeling guidance (EPA, Guidance on the Use of Models and Other Anal yses for Demonstrating Attainment of Air Quality Goals for Ozone, PM 2.5 , 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 f or the Atlanta PM 2.5 Nonattainment Area - May 24, 2010” (attached). The “Annual Reduction in PM 2.5 ( g/m 3 )” 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 PM 2.5 (ng/m 3 /TPD) ” i s calculated b y dividing the “Annual Reduction in PM2.5 ( g/m 3 ) ” b y the “TPD reduction”. The Powder Springs - Macland Aquatic Center PM 2.5 monitor (13 - 067 - 0004) did not start operating until February

5, 2003. As a result , this monitor was not included in the sensitivity anal ys is because it did not have a valid 5 - ye ar 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 analys is should not have any impact on the conclusions. **Table 1 : Summary of sensitivity analysis results for SO**  **2 emission controls at Plant Wansley**  **. Site Name**  **TPD reduction**  **Annual Reduction 1** 

**in PM 2.5**  **(** **g/m 3**  **) Normalized annual** 

**reduction in PM 2.5**  **(ng/m 3** **/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 - ye ar PM 2.5 concentrations (weighted for 2000 - 2004).**Table 2 : Summary of sensitivity analysis results for SO**  **2 emission controls at Plant Bowen**  **.**

**Site Name TPD**  **reduction Annual Reduction**  **1**

**in PM 2.5**  **(** **g/m 3**  **) Normalized annual** 

**reduction in PM 2.5**  **(ng/m 3** **/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 - ye ar PM 2.5 concentrations (weighted for 2000 - 2004). **Table 3**  **: Summary of sensitivity analysis results for SO 2**  **emission controls at Plant Yates.**  **Site Name TPD**  **reduction Annual Reduction**  **1**

**in PM 2.5**  **(** **g/m 3**  **) Normalized annual** 

**reduction in PM 2.5**  **(ng/m 3** **/TPD)** Doraville (13 - 0 89 - 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 - ye ar PM 2.5 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/m 3 as indicated in Table 4 .**Table 4**  **. Annual and Three -** **year Average Ambient PM** **2.5 Concentrations**  **.**

*T he Georgia Tech monitor stopped operation on December 29, 2008. **Discussion** The Atlanta PM 2.5 nonattainment area redesignation request and maintenance p lan 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 De cember 31, 2008. SO 2 controls were operating for the entire ye ar 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 SO 2 emissions for Plant Hammond, Plant Bowen, and Plant Wansley for the period 2003 through 2010. Also, the table includes the electrical generation, SO 2 emissions per 10 6 MWh generation, the average SO 2 emissions per 10 6 MWh generation for 2003 - 2007, the uncontrolled SO 2 in 2008 - 2010 (assuming average SO 2 emissions per 10 6 MWh generation for 2003 - 2007 x generation in 2008, 2009, 2010), and the controlled SO 2 in 2008 - 2010 (difference between uncontrolled and actual SO 2 emissions) . In addition, Table 5 shows the annual SO 2 emissions for Plant Yates (Unit 1) for the period 2008 through 2010. Also, the table includes the uncontrolled SO 2 in 2008 - 2010 (SO 2 emissions in 2008, 2009, 2010 divided by

0.05), and the controlled SO 2 in 2008 - 2010 (difference between uncontrolled and actual SO 2 emissions). Ambient PM 2.5 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**  Geo rgia 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 - 0 003) 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 SO 2 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 SO 2 emissions for each facility b y the normalized annual sensitivity in Tables 1 - 3 will quantify the impact of SO 2 emission controls from each facility on annual PM 2.5 concentrations. **Table 5**  **. Controlled SO**  **2 emissions**  **fro m**  **Plant Hammond, Plant Bowen, Plant Wansley , and**  **Plant Yates (Unit 1) in 2008 -**  **2010 .**  **Facility 2003**  **2004 2005**  **2006 2007**  **2008** ***** **2009** ***** **2010** ***** Hammond SO 2 (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 SO 2/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 SO 2 (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 SO 2/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** SO 2 (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 SO 2/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 SO 2 (tpy) 352 175.9 286

Uncontrolled 7,04 0.0 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 * SO 2 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

PM 2.5 monitors . The location of Plant Hammond, Plant Bowen, Plant Wansley and Plant Yates relative to the ten Atlanta PM 2.5 monitors is shown in Figure 1. The Yorkville monitor (13 - 223 - 0003) has the highest normalized sensitivity

to SO 2 emissions from Plant Wansley when compared to all the other Atlanta monitors (see Table 1). Therefore, a conservative approach would be to use the SO 2 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 SO 2 emissions from Plant Bowen when compared to the other Atlanta monitors (see Table 2). Therefore, a conservative approach would be to use the SO 2 normalized sensitivity at the Kennesaw -National Guard monitor for all the monitors in Atlanta. Since we did not perform SO 2 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 SO 2 normalized sensitivities from the Kennesaw National 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 SO 2 emissions from Plant Yates when compared to all the other Atlanta monitors (see Table 3). Therefore , a conservative approach would be to use the SO 2 normalized sensitivity at the Forest Park monitor for all the monitors in Atlanta. The maximum impact on annual PM 2.5 concentrations at each Atlanta PM 2.5 monitors due to SO 2 emission reductions that can b e 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 PM** **2.5 impact**  **on Atlanta**  **monitors from**  **SO 2**  **controls on Plant Hammond, Pl**  **ant Bowen, Plant Wansley** **, and Plant Yates in**  **2008 -** **2010 .** 

Controlled Emissions (TPY) Controlled

Emissions (TPD) Normalized

Sens itivity (ng/m 3 /TPD) Annual PM **2.5**

Impact ( g/m 3 ) 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 PM** **2.5 Concentrations**  **w ith/**  **without data substitution**  **and with/ without**  **Rule 391 -** **3 -**  **1 -**  **.02(2)(sss) .** 

Ambient PM 2.5 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)(s ss) 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 PM 2.5 annual measurements at the ten Atlanta PM 2.5 monitors from the application of SO 2 controls from Georgia’s Multipollutant Rule [391 - 3 - 1 - .02(2)(sss)] is 0.6 g/m 3 (rounded up from 0. 550 g/m 3 ). By adding this value to the 2008 - 2010 annual PM 2.5 design value results in revised 2008 - 2010 annual PM 2.5 design values that are all well below the 1997 annual PM 2.5 NAAQS of 15.0 g/m 3 (see Table 7 ). Therefore, removal of these controls would not have resulted in 2008 - 2010 annual PM 2.5 design value over the 1997 annual PM 2.5 NAAQS.