SENSITIVITY OF ANNUAL PM2.5 IN CHATTANOOGA TO SO2 EMISSION REDUCTIONS
RESULTING FROM Georgia’s Multipollutant Rule [391-3-1-.02(2)(sss)]

GA EPD performed an analysis of the sensitivity of PM2.5 concentrations
in the Chattanooga nonattainment area to reductions in SO2 emissions due
to the installation and operation of scrubbers at six 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
sensitivities were conducted, 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. 
Point-source sensitivities simulate actual expected reductions from the
installation of scrubbers (assuming a 95% control efficiency for SO2).
Six large coal-fired power plants in Georgia (installation of scrubbers
for SO2 removal) were modeled.  Note that Plant Hammond, Plant Bowen
Units 1&2, Plant Wansley Unit 1, and Plant Yates Unit 1 were not
included in the analysis since they will already have scrubbers
installed by 2009. The following is a detailed list of the six
facilities that were modeled:

Scrubbers at Bowen: Installation of scrubbers on Plant Bowen units 3-4
(average reduction of 218 tons-per-day of SO2 compared to
pre-installation emissions; assuming a 95% control efficiency for SO2).

Scrubbers at Branch: Installation of scrubbers and selective catalytic
reduction devices (SCRs) on Plant Branch units 1-4 (average reduction of
183 tons-per-day of SO2 compared to pre-installation emissions; assuming
a 95% control efficiency for SO2).

Scrubbers at McDonough: Installation of scrubbers on Plant McDonough
units 1-2 (average reduction of 58.8 tons-per-day of SO2 compared to
pre-installation emissions; assuming a 95% control efficiency for SO2).

Scrubbers at Scherer: Installation of scrubbers on Plant Scherer units
1-4 (average reduction of 278 tons-per-day of SO2 compared to
pre-installation emissions; assuming a 95% control efficiency for SO2).

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).

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.

Sensitivity analysis results for the Rossville site (13-295-0002) in
Chattanooga are reported in Table 1. 

Table 1: Summary of sensitivity analysis results for the Rossville site
(AIRS ID 13-295-0002)

Sensitivity	TPD reduction	Annual Reduction1 in PM2.5 ((g/m3)	Normalized
annual reduction in PM2.5 (ng/m3/TPD)

Scrubbers at Bowen	217.72	0.175	0.805

Scrubbers at Branch	183.27	0.089	0.488

Scrubbers at McDonough	58.84	0.039	0.661

Scrubbers at Scherer	277.62	0.122	0.439

Scrubbers at Wansley	103.88	0.050	0.484

Scrubbers at Yates	137.20	0.076	0.556

1Scaled relative to the observed speciated 5-year PM2.5 concentrations
(weighted for 2000-2004)

Clean Data Determination

On May 31, 2011, EPA promulgated its determination (76 FR 31239) that
the Chattanooga 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 2007-2009 period which showed a design value of 12.7 µg/m3.  

Table 2.  Annual and Three-year Average Ambient PM2.5 Concentrations

Year	Monitor

13-295-0002

((g/m3)	Monitor

47-065-0031

((g/m3)	Monitor

47-065-1011

((g/m3)	Monitor

47-065-4002

((g/m3)

2003	15.9	16.5	14.3	14.9

2004	14.9	15.6	13.3	14.5

2005	16.4	16.1	13.8	15.5

2006	14.4	14.3	13.1	15.0

2007	13.7*	14.9	14.2	15.0

2008	12.5	12.3	11.4	12.7

2009	10.7	10.5	9.5	10.5

2010	8.9	12.0	13.3	11.7

2007-2009	12.3*	12.6	11.7	12.7

2008-2010	10.7	11.6	11.4	11.6

     *Values subject to data substitution (76 FR 15895)

Discussion

The Georgia portion of the Chattanooga 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 actually started on five units in
May 2008.  SO2 controls were operating for the entire year of 2009 as
follows:

Plant Hammond – controls on 4 of 4 units;

Plant Bowen – controls on 2 of 4 units; and

Plant Wansley – controls on 1 of 2 units.

Table 3 shows the annual SO2 emissions for the coal-fired facilities in
North Georgia for the period 2003 through 2010.  The table also 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 2009 (assuming average SO2 emissions per 106 MWh
generation for 2003-2007 x 2009 generation),  and the controlled SO2 in
2009 (difference between uncontrolled and actual 2009 SO2 emissions).  

Table 3.  Annual SO2 Emissions and Generation (106 MWh) from Plant
Hammond, Plant Bowen, and Plant Wansley, 2003 - 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





	32,883.4



Controlled





	31,983.4













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





	183,283.2



Controlled





	128,483.2













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





	77,849.1



Controlled





	70,449.1

	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

The “Controlled” value in Table 3 is the amount of SO2 emission
reductions that can be attributed to Georgia’s Multipollutant Rule
[391-3-1-.02(2)(sss)].  By multiplying the controlled SO2 emissions for
each facility by the normalized annual sensitivity in Table 1 will
quantify the impact of SO2 emission controls from each facility on
annual PM2.5 concentrations.  The location of Plant Hammond, Plant
Bowen, and Plant Wansley relative the four Chattanooga PM2.5 monitors is
shown in Figure 1.

Figure 1.  Map of Plant Hammond, Plant Bowen, and Plant Wansley relative
the four Chattanooga PM2.5 monitors.

The Rossville monitor (13-295-0002) is the closest monitor to Plant
Wansley and Plant Hammond (see Table 4).  Also, the Rossville monitor
and Maxwell Road/ East Ridge monitor (47-065-0031) are approximately
equal distance from Plant Bowen.  Therefore, it would be a conservative
approach to use the normalized sensitivities from the Rossville monitor
to represent the impact at all four Chattanooga monitors.

Table 4.  Distance (km) from Plant Hammond, Plant Bowen, and Plant
Wansley to Chattanooga monitors.

Monitor	Facility	Distance (km)

47-065-1011 (Soddy-Daisy High School)	Plant Wansley	202.3

47-065-1011 (Soddy-Daisy High School)	Plant Bowen	125.2

47-065-1011 (Soddy-Daisy High School)	Plant Hammond	109.7

47-065-0031 (Maxwell Road/ East Ridge)	Plant Wansley	176.4

47-065-0031 (Maxwell Road/ East Ridge)	Plant Bowen	100.8

47-065-0031 (Maxwell Road/ East Ridge)	Plant Hammond	82.8

47-065-4002 (Siskin Drive/UTC)	Plant Wansley	183.2

47-065-4002 (Siskin Drive/UTC)	Plant Bowen	108.2

47-065-4002 (Siskin Drive/UTC)	Plant Hammond	88.6

13-295-0002 (Rossville)	Plant Wansley	175.4

13-295-0002 (Rossville)	Plant Bowen	100.9

13-295-0002 (Rossville)	Plant Hammond	80.6



Since a sensitivity run was not performed for Plant Hammond, we can
estimate the normalized annual sensitivity for this facility by
multiplying the normalized sensitivity for Plant Bowen by 1.25
(multiplier is calculated by 1.0/[1.0-(100.9-80.6)/100.9]) to account
for the fact that Plant Hammond (80.6 km) is 20% closer to the Rossville
monitor than Plant Bowen (100.9 km).  This will result in a normalized
annual sensitivity of 0.805 x 1.25 = 1.006 ng/m3/TPD.

Table 5.  Annual PM2.5 impact on Chattanooga monitors from SO2 controls
on Plant Hammond, Plant Bowen, and Plant Wansley in 2009

	Controlled Emissions (TPY)	Controlled Emissions (TPD)	Normalized
Sensitivity (ng/m3/TPD)	Annual PM2.5 Impact (g/m3)

Plant Bowen	128,483.20	352.01	0.805	0.283

Plant Hammond	31,983.40	87.63	1.006	0.088

Plant Wansley	70,449.10	193.01	0.484	0.093

TOTAL



0.465



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Table 6.  Annual and Three-year Average Ambient PM2.5 Concentrations

Year	Monitor

13-295-0002

((g/m3)	Monitor

47-065-0031

((g/m3)	Monitor

47-065-1011

((g/m3)	Monitor

47-065-4002

((g/m3)

2007-2009 Design Value

with Rule 391-3-1-.02(2)(sss)	12.3	12.6	11.7	12.7

2007-2009 Design Value

without Rule 391-3-1-.02(2)(sss)	12.8	13.1	12.2	13.2



