Appendix S.1 

Attainment Test 
 

TABLE OF CONTENTS 

I. Attainment Demonstration........................................................................................................................1

II. Modeled Attainment Test.....................................................................................................................1

III. Additional Corroborative Analyses And Weight Of Evidence Determination......................................4

A. Alternative DVF Calculation ................................................................................................ 4 

B Air Quality Modeling Metrics................................................................................................ 7 

C. Air Quality Modeling Results From Other Studies............................................................. 14 

D. Air Quality Trends and Additional Reductions in Emissions............................................. 15 

E. Local Measures not Modeled .............................................................................................. 17 

F. Weight of Evidence Conclusions ........................................................................................ 19 

IV Unmonitored Area Analysis .................................................................................................................20
 

LIST OF FIGURES 

Figure L-1: Charts the number of days greater than 90 degree F versus the 4th highest 8-hour ozone value 

for the Metrolina area...........................................................................................................................6

Figure L-2: Area for which the air quality metrics were applied.................................................................8

Figure L-3: Persistence and Severity for the Metrolina Area. .....................................................................9

Figure L-4: Daily AQI counts for the Metrolina Area...............................................................................10

Figure L-5: Hourly AQI Count for the Metrolina Area. ............................................................................11

Figure L-6: Percent Occurrence of Daily Maximum Code Yellow and Code Orange Grid Cells for the 

Metrolina Area. ..................................................................................................................................12

Figure L-7: Percent Occurrence of Hourly Maximum Code Yellow and Code Orange Grid Cells for the 

Metrolina Area. ..................................................................................................................................13

Figure L-8: Location and size of the Duke Energy facilities located in the vicinity of the Metrolina 

nonattainment area. ............................................................................................................................16

Figure L-9: Ozone Monitors and 2009 Modeled Spatial Field ..................................................................21

Figure L-10: Ozone Monitors and 2012 Modeled Spatial Field ................................................................21
 

LIST OF TABLES 

Table L-1: USEPA’s Recommendation for Defining “Nearby” Cells.........................................................2

Table L-2: Metrolina Attainment Test Results for 2009..............................................................................3

Table L-3: Metrolina Attainment Test Results for 2011..............................................................................4

Table L-4: Five-Year Average Alternative Attainment Test Results for 2009............................................5

Table L-5: Five-Year Average Alternative Attainment Test Results for 2011............................................6

Table L-6: Total number of grid cells for the AQI Categories 2002 vs 2009............................................14

Table L-7: Total number of grid cells for the AQI Categories 2002 vs 2011............................................14

Table L-8: Metrolina DVFs based on EAC Modeling...............................................................................14

Table L-9: Metrolina DVFs based on the USEPA’s CAIR Modeling.......................................................15

Table L-10: Design Values (ppb) for the North Carolina Monitors in the Metrolina Area.......................15

Table L-11: Utility NOx Emission Reductions since 2006 Ozone Season................................................16
1 

 ATTAINMENT TEST 

I. Attainment Demonstration 

This Appendix summarizes the procedures that were used to demonstrate attainment of the 8-hour 

ozone NAAQS in this SIP package. The modeling exercises for the 2011 attainment year were performed 

by the NCDAQ, with the results reviewed in close collaboration with the SCDHEC. As described in the 

USEPA’s April 2007 Final Guidance On The Use Of Models And Other Analyses for Demonstrating 

Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze (“Attainment Guidance”), an 

attainment demonstration consists of: (a) analyses which estimate whether selected emissions reductions 

will result in ambient concentrations that meet the NAAQS, and (b) an identified set of control measures 

which will result in the required emissions reductions. The necessary emission reductions for both of 

these attainment demonstration components may be determined by relying on results obtained with air 

quality models. 

Section 3.0 of the Attainment Guidance recommends applying both a modeled attainment test and a 

subsequent screening test to the air quality modeling results to determine if the 8-hour ozone NAAQS 

will be met. Additional technical or corroboratory analyses may also be used as part of a “weight of 

evidence” determination to supplement the modeled attainment test and to further support a 

demonstration of attainment of the NAAQS. 

The modeled attainment test, additional corroborative analyses and weight of evidence, and 

unmonitored area analysis are described in further detail in the remaining portions of this Appendix, 

detailing how the respective test or analysis was performed and applied to the attainment demonstration. 

II. Modeled Attainment Test 

The modeled attainment test is the practice of using an air quality model to simulate baseline (i.e., 

current) and future air quality. For the 8-hour ozone NAAQS, the baseline and future model estimates are 

used in a “relative” rather than “absolute” sense. Specifically, the ratio of the air quality model’s future to 

baseline predictions is calculated at each ozone monitoring site. These monitoring site-specific ratios are 

called relative response factors (RRF). Future ozone design values (DVF) are then estimated at each 

monitor by multiplying the monitor-specific baseline ozone design value (DVB) by the modeled relative 

response factor for each monitor. If the resulting predicted site-specific DVFs are < 82 parts per billion 

(ppb), a clear demonstration of predicted attainment is shown. If the predicted DVFs are > 82 ppb and <

87 ppb, then a weight of evidence demonstration must be submitted that supports a demonstration of 

attainment. For DVFs > 87ppb, the Attainment Guidance states that more qualitative results are less 

likely to support a conclusion differing from the outcome of the modeled attainment test. Equation L-1 

presents the modeled attainment test, applied at monitoring site “x” as described in Section 4.0 of the 

Attainment Guidance. 

 Future Design Value Equation: 

 (DVF) = (RRF) x (DVB) 

Where (DVB) = the baseline design value monitored at site “x,” ppb 

 = the average (of the three) design value periods which include the baseline inventory 

year (i.e. the average of the 2000-2002, 2001-2003, and 2002-2004 design values 

periods for the 2002 baseline inventory year). 
2 

 (RRF) = the ratio of the future 8-hour daily maximum concentration predicted “nearby” a 

monitor (averaged over each day of the episode) to the current 8-hour daily maximum 

concentration predicted “nearby” the monitor (averaged over each day of the episode). 

 (DVF) = the estimated future design value, ppb. 

It is important to consider an array of cells “nearby” a monitor rather than focusing on the individual 

cell containing the monitor. This allows for variations in the model performance where the peak ozone 

may not occur in the grid cell that contains the monitor but rather nearby the monitor. Table L-1 provides 

the USEPA’s recommendations for defining “nearby” cells for grid systems having cells of various sizes. 

Since the attainment demonstration modeling was performed using a 12-kilometer grid resolution, the size 

of the array for “nearby” cells was 3 x 3. 

Table L-1: USEPA’s Recommendation for Defining “Nearby” Cells 

Size of Cell 

(km) 

Size of the Array of 

“Nearby” Cells 

<5 7 x 7 

>5-8 5 x 5 

>8-15 3 x 3 

>15 1 x 1 

The RRF is calculated by taking the ratio of the mean future year modeling 8-hour ozone daily 

maximum to the mean baseline year modeling 8-hour ozone daily maximum “near” the monitor. 

Relative Response Factor Equation: 

RRF = mean future yr. 8-hr daily max “near” monitor “x” 

 mean baseline yr. 8-hr daily max “near” monitor “x” 

Section 14.1.1 of USEPA’s Attainment Guidance outlines the process for determining which days 

are used in the RRF calculation. The day selection process starts by identifying all the days in the 

baseline modeling that has a modeled daily maximum 8-hour average ozone equal to or greater than 

85 ppb. If there are 10 or more days greater than 85 ppb, then 85 ppb is used as the cutoff in the RRF 

calculation. If there are fewer than 10 days with a modeled daily maximum 8-hour average ozone equal 

to or greater than 85 ppb, then the threshold is reduced by 1 ppb until there are at least 10 days identified 

for use. If there are fewer than 10 days with a modeled daily maximum 8-hour average ozone equal to or 

greater than 70 ppb, then all days at 70 ppb and higher are used in the RRF calculation and consideration 

of modeling another episode should be explored. 

The DVB, for purposes of the modeled attainment test, is defined in the Attainment Guidance by one 

of four methods: 

1. The design value period (i.e. the average 4th highest value for the 3-year period used to designate 

an area “nonattainment,” for this nonattainment designation, the period from 2001 to 2003); 
3 

2. The average 4th highest value for the 3-yr period straddling the baseline inventory year (e.g., the 

2001-2003 design value period for the 2002 baseline inventory year); 

3. The highest of the three design value periods which include the baseline inventory year (e.g., the 

2000-2002, 2001-2003, 2002-2004 design value periods for a 2002 baseline inventory year); and 

4. The average of the three design value periods which straddle the baseline inventory year (e.g., the 

average of the 2000-2002, 2001-2003, and 2002-2004 design value periods for a 2002 baseline 

inventory year). 

The USEPA recommends the fourth method (average of the three design value periods straddling the 

baseline year), which is the DVB shown in Table 2-2 and Table 2-3 at each ozone monitoring site in the 

Metrolina region. 

As mentioned earlier in this document, the mandated attainment date for the Metrolina nonattainment 

area is June 15, 2010, which requires the 1997 8-hour ozone standard to be attained by the end of 2009. 

Since the NCDAQ and the SCDHEC believe that it may be necessary to request two one-year extensions 

of the attainment date, the expected attainment year is 2011. The results for both years have been 

calculated. Table L-2 lists the attainment test results for 2009 by monitor in the Metrolina area. 

Similarly, Table L-3 lists the attainment test results for 2011. In both tables, the first column is the 

monitoring site, then the county of the monitoring site’s location, followed by the DVB used for the 

attainment test. The next series of columns are the number of days used in the calculation, the ozone 

level threshold needed to reach at least 10 days for RRF, the calculated RRF, and finally the resulting 

DVF for the 2009 and 2011 attainment years, respectively. The bold italicized DVFs are values that fall 

within the range where additional weight of evidence is needed to demonstrate attainment. Based on the 

2009 modeling, half of the monitors in the Metrolina nonattainment area have predicted DVFs that fall 

below 82 ppb and the other half fall between 82 ppb and 87 ppb. By 2011, only two of the monitors are 

predicted to have DVFs that fall between 82 ppb and 87 ppb with the other six sites falling below 82 ppb. 

With either the 2009 or the 2011 modeling predictions, additional weight of evidence is required to 

demonstrate attainment. The NCDAQ and the SCDHEC believe that the weight of evidence presented in 

Section 3 fully supports a demonstration of attainment. 

Table L-2: Metrolina Attainment Test Results for 2009 

Monitoring Site County DVB 

(ppb) 

Number of 

Days used 

in RRF 

Ozone 

Threshold 

(ppb) 

RRF DVF 

(ppb) 

Arrowood Mecklenburg 84.7 18 85 0.883 74 

County Line Mecklenburg 97.3 12 85 0.875 85 

Crouse Lincoln 90.7 10 84 0.867 78 

Enochville Rowan 97.0 12 85 0.870 84 

Garinger (Plaza) Mecklenburg 95.3 20 85 0.888 84 

Monroe Union 87.0 11 79 0.884 76 

Rockwell Rowan 97.3 12 83 0.861 83 

York York, SC 83.0 10 82 0.861 71 
4 

Table L-3: Metrolina Attainment Test Results for 2011 

Monitoring Site County DVB 

(ppb) 

Number of 

Days used 

in RRF 

Ozone 

Threshold 

(ppb) 

RRF DVF 

(ppb) 

Arrowood Mecklenburg 84.7 15 85 0.854 72 

County Line Mecklenburg 97.3 12 85 0.846 82 

Crouse Lincoln 90.7 10 83 0.829 75 

Enochville Rowan 97.0 13 85 0.837 81 

Garinger (Plaza) Mecklenburg 95.3 20 85 0.862 82 

Monroe Union 87.0 12 78 0.858 74 

Rockwell Rowan 97.3 10 83 0.837 81 

York York, SC 83.0 13 81 0.841 69 

III. Additional Corroborative Analyses And Weight Of Evidence Determination 

As part of the weight of evidence determination, the following analyses will be evaluated: 

• Alternative DVFs calculations, 

• Metrics of air quality modeling results, 

• Air quality modeling results from other studies, 

• Observed air quality trends and additional reductions in emissions, and 

• Local measures not modeled. 

The weight of evidence determination is a supplement to the modeled attainment test and further 

supports that the area will attain the NAAQS for 8-hour ozone by the attainment date. Based on the air 

quality measurements for 2007 through 2009, a monitor in the Metrolina nonattainment area has a design 

value above the 1997 8-hour ozone standard. However, the Metrolina area does have clean data for 2009 

and meets the requirements to request a one-year extension of the attainment date. Since the ambient air 

quality measurements for 2008 were high, the NCDAQ believes that it may be necessary to request a 

second one-year extension of the attainment date. 

 A. Alternative DVF Calculation 

The NCDAQ used the USEPA recommended method of calculating the DVB in its modeled 

attainment test. However, the NCDAQ has commented several times on various draft versions of the 

attainment guidance that they do not believe that a weighted DVB is appropriate and that a DVB 

calculated using a straight average minimizes the impacts of any abnormally hot/dry or cool/wet 

meteorological conditions. As part of the weight of evidence demonstration, the NCDAQ proposes an 

alternative method to calculate the DVB and presents the modeled attainment test results with this 

alternative DVB. 
5 

The USEPA recommends calculating the DVB by averaging the three design value periods that 

straddle the baseline inventory year. This methodology results in a center weighting of annual 4th highest 

ozone concentrations around the baseline inventory year because the three design value periods averaged 

contain overlapping data. The simplified recommended DVB calculation for this SIP modeling exercise 

is shown below. 

Recommended Baseline Design Value Equation: 

 1*(2000 4th Highest) + 2*(2001 4th Highest) + 3*(2002 4th Highest) 

DVB = + 2*(2003 4th Highest) + 1*(2004 4th Highest) 

 9 

The weighting scheme of annual 4th highest ozone concentrations in the recommended DVB 

calculation weights the center, or third, year three times more than that of the first or last year and one and 

half times more than that of the second or forth year. If this third year is an abnormally hot/dry or 

cool/wet period, the unusual meteorological conditions and resulting air quality conditions will be 

amplified upward or downward in the modeled attainment exercise. 

To minimize potential impacts of any abnormal meteorological conditions while still considering 

ozone conditions across a five-year span, an alternative DVB calculation that does not weight any of the 

years more than another, but is a straight average of annual 4th highest ozone concentrations for the fiveyear span centered on the baseline inventory year was considered. 

Recommended Baseline Design Value Equation: 

 2000 4th Highest + 2001 4th Highest + 2002 4th Highest 

DVB = 2003 4th Highest + 2004 4th Highest 

 5 

The results of applying the five-year straight average DVB to the remainder of the Modeled 

Attainment Test equations, at each monitoring site in the Metrolina region are shown in Table L-4 and 

Table L-5. 

Table L-4: Five-Year Average Alternative Attainment Test Results for 2009 

Monitoring Site County 

DVB 

5-Year Straight 

Average 

2000-2004 

(ppb) 

RRF DVF 

(ppb) 

Arrowood Mecklenburg 83.4 0.883 73 

County Line Mecklenburg 95.6 0.875 83 

Crouse Lincoln 89.2 0.867 77 

Enochville Rowan 94.4 0.870 82 

Garinger (Plaza) Mecklenburg 93.8 0.888 83 

Monroe Union 84.6 0.884 74 

Rockwell Rowan 94.6 0.861 81 

York York, SC 79.8 0.861 68 
6 

Table L-5: Five-Year Average Alternative Attainment Test Results for 2011 

Monitoring Site County 

DVB 

5-Year Straight 

Average 

2000-2004 

(ppb) 

RRF DVF 

(ppb) 

Arrowood Mecklenburg 83.4 0.854 71 

County Line Mecklenburg 95.6 0.846 80 

Crouse Lincoln 89.2 0.829 73 

Enochville Rowan 94.4 0.837 79 

Garinger (Plaza) Mecklenburg 93.8 0.862 80 

Monroe Union 84.6 0.858 72 

Rockwell Rowan 94.6 0.837 79 

York York, SC 79.8 0.841 67 

In comparison to the respective DVF values found in Table L-2 and Table L-3, the DVF values in 

Table L-4 and Table L-5 are slightly lower at each monitoring site. These differences were expected, as 

2002 was an abnormally hot and dry year throughout the Southeast with ozone concentrations that were 

higher than in the surrounding years of 2000, 2001, 2003, and 2004. Figure L-1 below illustrates this by 

charting the number of days with temperatures greater than 90 degrees F versus the maximum fourth 

highest 8-hour ozone value for the Metrolina area. Comparing 2002 to the surrounding years used in the 

DVB (2000, 2001, 2003 and 2004), 2002 had significantly more days with greater than 90 degrees oF 

temperatures. Similarly, the maximum fourth highest 8-hour ozone value was approximately five ppb 

higher than the surrounding years used in the DVB. 

0.080

0.085

0.090

0.095

0.100

0.105

0.110

0.115

0

10

20

30

40

50

60

70

80

Max 4th Highest

# Days Hi Temp 

≥ 90F May-Sep

Metrolina 8-hour Ozone - # Days Hi ≥90F vs Max 

4th Highest

# Days Temperature >90F Max 4th Highest

Figure L-1: Charts the number of days greater than 90 degree F versus the 4th highest 8-hour 

ozone value for the Metrolina area. 
7 

Thus, the recommended DVB calculation weighted the higher air quality conditions several times 

more than in the NCDAQ alternative DVB calculations. The NCDAQ firmly believes that the nonweighted or straight five-year average approach to the DVB calculation is more appropriate and 

minimizes dramatic fluctuations in meteorological and air quality conditions from year to year. This 

would be the case whether the center weighted year was an abnormally hot/dry year or a cool/wet year. 

While none of the monitoring sites in the Metrolina region had DVF values at or above 85 ppb in 

Table 3.1-1 or Table 3.1-2 using the NCDAQ alternative DVB calculation, there are still three monitors in 

Table 3.1-1 that have DVFs that fall between 82 ppb and 87 ppb. This continues to indicate that some 

additional weight of evidence should still be included to demonstrate attainment. These results are not 

inconsistent with what was concluded using all recommended modeled attainment test calculations. 

 B Air Quality Modeling Metrics 

In Section 7.0 of the Attainment Guidance, various aspects of air quality models, modeled 

performance, and uncertainties associated with the length of modeled episodes and limited observational 

datasets are described. A series of three additional air quality modeling outputs or metrics is 

recommended to provide assurance the modeled demonstration indicates attainment. These metrics look 

at the relative change between the baseline and future years modeling and help to demonstrate how 

widespread the improvement in air quality is expected to be in the future. Although the final guidance did 

not recommend percentage cut points that corresponds to supportive weight of evidence, an earlier draft 

version of the Attainment Guidance recommends that the metrics should be at least 80 percent or higher. 

As described in Section 7.1 of the Attainment Guidance, the modeling data for the area displayed in 

Figure 5.2-1 from the 2002, 2009, and 2011 modeling were applied to the following metrics: 

1. Relative change in surface grid-hours greater than 84 ppb. This metric is termed PersistenceHour and is defined as the number of grid-cells in a given region with predicted hourly 8-

hour ozone concentrations greater than 84 ppb. The relative change in Persistence-Hour is 

presented as a percent reduction computed for the modeling period May through September 

from the baseline year case to the future year case. 

2. Relative change in the number of grid cells with predicted 8-hour daily maxima greater than 

84 ppb. This metric is termed Persistence-Daily metric and is similar to Persistence-Hour, 

but uses the modeled daily maximum 8-hour ozone concentrations greater than 84 ppb 

instead of the hourly 8-hour ozone concentrations. The relative change in Persistence-Daily 

is also presented as a percent reduction computed for the modeling period May through 

September from the baseline year case to the future year case. 

3. Relative change in the sum of hourly predictions greater than 84 ppb. This metric is termed 

Severity-Hour and is defined as the sum of all grid-cells with predicted hourly 8-hour ozone 

concentrations greater than 84 ppb. Given the definition of Persistence, this Severity could 

be considered as a weighted form of the Persistence metric. The relative change in Severity 

is also presented as a percent reduction computed for the modeling period May through 

September from the baseline year case to the future year case. 

In addition to the three recommended metrics, two additional metrics were computed to create a 

comprehensive corroborative analysis. The two additional metrics are: 
8 

4. Relative change in the sum of the predicted 8-hour daily maxima greater than 84 ppb. 

Severity-Daily metric is similar to Severity-Hour, but uses the modeled daily maximum 8-

hour ozone concentrations greater than 84 ppb instead of the hourly 8-hour ozone 

concentrations. The relative change in Severity-Daily is also presented as a percent reduction 

computed for the modeling period May through September from the baseline year case to the 

future year case. 

5. Air Quality Index (AQI) Counts. The AQI Counts metric is a count of the number of gridcells with predicted maximum 8-hour ozone concentrations sorted within each of the Code 

Green, Yellow, Orange and Red categories, as defined by the USEPA’s AQI Index. As with 

the persistence and severity metrics, the AQI counts metric can be applied to both hourly and 

daily maximum 8-hour ozone concentrations. AQI Counts are presented as percentages of 

the total number of grid-cells within the study region. 

The metrics described above were applied to the modeling results for just of the nonattainment area. 

Below, Figure L-2 depicts the region for which this modeling data was extracted for the 2002 baseline 

and the 2009 and 2011 attainment year modeling runs. 

Figure L-2: Area for which the air quality metrics were applied. 

The results from each of the five air quality modeling metric calculations demonstrated significant 

reductions of greater than 85 percent in the 2009 future year air quality modeling and greater than 90 

percent in the 2011 future year air quality modeling for days that modeled above the NAAQS in the 

Metrolina nonattainment area. Each metric demonstrated very large relative reductions for 2009 and 

demonstrated more substantial reductions for 2011. It is important to note that the relative reductions in 

all metrics well surpassed the draft version of the Attainment Guidance recommendation of 80 percent for 

these particular calculations. 

It should be noted that a minor alteration in the spatial distribution of the emissions inventory in the 

2011 air quality modeling required a rerun of the air quality model for the 2002 baseline year to 

appropriately calculate the 2011 based RRFs without introducing any modeling bias due to the minor 

emissions inventory spatial distribution alteration. So, there are subtle differences in the hourly and daily 

grid cell counts for 2002. 

Figure L-3 presents the relative reductions calculated in the first four metrics described above. The 

left two bars are the Persistence-Hour and Persistence-Daily reductions, and the right two bars are the 
9 

Severity-Hour and Severity-Daily reductions. The 2009 modeling results demonstrate a 90.0 percent 

reduction in persistence of hourly maximum ozone and 86.4 percent reduction in persistence of daily 

maximum ozone. The severity reductions for 2009 are on a similar scale of 90.3 percent and 86.9 percent 

reduction for hourly and daily maximum ozone, respectively. The 2011 modeling results demonstrate a 

97.4 percent reduction in persistence of hourly maximum ozone and 95.9 percent reduction in persistence 

of daily maximum ozone. The severity reductions for 2011 are equally on a similar scale of 97.5 percent 

and 96.1 percent reduction for hourly and daily maximum ozone, respectively. 

60

65

70

75

80

85

90

95

100

Persistance Severity

% Reduction

% Reduction in Persistance (# Grid Cells) and 

Severity (Sum Cij_85) of Hourly & Daily Max O3

2002 vs 2009

Hourly

Daily

60

65

70

75

80

85

90

95

100

Persistance Severity

% Reduction

% Reduction in Persistance (# Grid Cells) and 

Severity (Sum Cij_85) of Hourly & Daily Max O3

2002 vs 2011

Hourly

Daily

Figure L-3: Persistence and Severity for the Metrolina Area. 
10 

Equating the 86.4 percent relative reduction in the daily maximum ozone persistence to AQI Counts, 

the top portion of Figure L-4 demonstrates a drop from 339 grid cells in the Code Orange and Red levels 

in the 2002 baseline modeling to 46 grid cells in the 2009 future modeling. Furthermore, the number of 

grid cells in the Code Yellow and above (>65 ppb) range is reduced by 51.9 percent from 3,600 grid cells 

in 2002 to 1,733 grid cells in 2009. When the 2011 future year modeling is considered in the bottom 

portion of Figure 3.2-3, the 95.9 percent relative reduction in the daily maximum ozone persistence 

translates into a drop from 317 grids cells in the Code Orange and Red levels in 2002 to only 13 grid cells 

in 2011. Additionally, the number of grid cells Code Yellow and greater is reduced by 65.0 percent from 

3,503 grid cells in 2002 to 1,227 grid cells in 2011. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Daily 2002 Daily 2009

% Grid Cells in Region

Daily 8-hr AQI Counts (2002 vs 2009)

Orange

Yellow

Green

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Daily 2002 Daily 2011

% Grid Cells in Region

Daily 8-hr AQI Counts (2002 vs 2011)

Orange

Yellow

Green

Figure L-4: Daily AQI counts for the Metrolina Area. 
11 

The hourly AQI Counts are equally encouraging. For 2009, Figure L-5 (top) displays the 90.0 

percent relative reduction in hourly persistence in terms of the AQI counts. It corresponds to a reduction 

from 1,315 hourly grid cells in the Code Orange and Red levels in the baseline modeling to only 131 

hourly grid cells in the 2009 future year modeling. Looking at all hourly grid cells Code Yellow and 

greater, the count is reduced from 24,230 to 8,959, which translates to a 63.0 percent reduction. Figure L5 (bottom) presents the 97.4 percent relative reduction in hourly persistence in terms of the AQI counts 

for 2011. This reduction translates to a reduction from 1,195 hourly grid cells in the Code Orange and 

Red levels in 2002 to only 31 hourly grid cells in 2011. The reduction in hourly grid cell Code Yellow 

and greater is equally impressive with a reduction from 23,336 to 5,874. This is a 74.8 percent reduction 

from 2002 to 2011. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Hourly 2002 Hourly 2009

% Grid Cells in Region

Hourly 8-hr AQI Counts (2002 vs 2009)

Orange

Yellow

Green

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Hourly 2002 Hourly 2011

% Grid Cells in Region

Hourly 8-hr AQI Counts (2002 vs 2011)

Orange

Yellow

Green

Figure L-5: Hourly AQI Count for the Metrolina Area. 
12 

The tremendous improvements in air quality from the 2002 baseline year to the 2009 and 2011 future 

years can further be illustrated by looking at just the percentage of occurrence of the Code Yellow and 

Orange grid cells throughout the Metrolina area. Figures L-6 and L-7 present metric for 2009 (top) and 

2011 (bottom) in terms of the daily and hourly percentage of occurrence, respectively. 

0

5

10

15

20

25

30

35

40

45

50

Daily 2002 Daily 2009

% Occurence in Region

% Occurence of Daily Max Yellow and Orange 

(2002 vs 2009)

Orange

Yellow

0

5

10

15

20

25

30

35

40

45

50

Daily 2002 Daily 2011

% Occurence in Region

% Occurence of Daily Max Yellow and Orange 

(2002 vs 2011)

Orange

Yellow

Figure L-6: Percent Occurrence of Daily Maximum Code Yellow and Code Orange Grid Cells for 

the Metrolina Area. 
13 

0

2

4

6

8

10

12

14

Hourly 2002 Hourly 2009

% Occurence in Region

% Occurence of Hourly Max Yellow and Orange 

(2002 vs 2009)

Orange

Yellow

0

2

4

6

8

10

12

14

Hourly 2002 Hourly 2011

% Occurence in Region

% Occurence of Hourly Max Yellow and Orange 

(2002 vs 2011)

Orange

Yellow

Figure L-7: Percent Occurrence of Hourly Maximum Code Yellow and Code Orange Grid Cells 

for the Metrolina Area. 

Finally, all of the AQI grid cell counts displayed in Tables L-4 through L-7 are summarized below. 

Table L-6 contains all of the grid cell counts for both the Hourly and Daily AQI Count analyses for the 

2002 baseline and 2009 future year modeling. Similarly, Table L-7 contains all of the grid cell counts for 

both the Hourly and Daily AQI Count analyses for the 2002 baseline and 2011 future year modeling. 
14 

Table L-6: Total number of grid cells for the AQI Categories 2002 vs 2009. 

Grid Cells Grid Cells

Daily 2002 Daily 2009 Hourly 2002 Hourly 2009

Green 4304 6171 165466 180737

Yellow 3261 1687 22915 8828

Orange 339 46 1315 131

total 7904 7904 189696 189696

Table L-7: Total number of grid cells for the AQI Categories 2002 vs 2011. 

Daily 2002 Daily 2011 Hourly 2002 Hourly 2011

Green 4401 6677 166330 183822

Yellow 3186 1214 22171 5843

Orange 317 13 1195 31

total 7904 7904 189696 189696

 C. Air Quality Modeling Results From Other Studies 

Another recommended weight of evidence analysis is to review other air quality modeling results that 

included the Metrolina nonattainment area to determine how other modeling results compare to the 

attainment demonstration. There are two air quality modeling studies to which results are available for 

the Metrolina area. 

The first is the EAC modeling that the NCDAQ performed for the EAC areas within North Carolina. 

Since the modeling domain for this analysis covered the majority of North Carolina, including the 

Metrolina nonattainment area, the modeling results can be easily compared to the attainment 

demonstration. There are some differences between the two modeling exercises. One difference is that 

the EAC modeling was carried out on 4 episodes (one in 1995, two in 1996 and one in 1997) for a total of 

sixteen days. Another is the DVB is based on the higher of the 1999-2001 or 2001-2003 design values. 

Finally, the EAC modeling did not model 2009, but there are results for 2007 and 2012. Table L-8 

displays the EAC modeling results for the Metrolina monitors for both of these future years. 

Table L-8: Metrolina DVFs based on EAC Modeling 

2007 2012 

Monitoring Site County DVB 

(ppb) RRF DVF 

(ppb) RRF DVF (ppb) 

Arrowood Mecklenburg 092 0.891 82 0.848 78 

County Line Mecklenburg 101 0.861 87 0.802 81 

Crouse Lincoln 92 0.870 80 0.826 76 

Enochville Rowan 99 0.879 87 0.818 81 

Garinger (Plaza) Mecklenburg 98 0.888 87 0.816 80 

Monroe Union 88 0.852 75 0.795 70 

Rockwell Rowan 100 0.870 87 0.800 80 

As can be seen from the EAC modeling, although there are still four monitors slightly above the 8-

hour ozone standard in 2007, all of the monitors are well below the standard by 2012. It should be noted 

that for the Greensboro/Winston-Salem/High Point EAC area, the EAC attainment test results predicted 

the highest monitor in the area to be at 83 ppb in 2007 and the actual 2005-2007 design value for the area 

was 83 ppb. 
15 

Another air quality modeling exercise that contained results for the Metrolina nonattainment area is 

the USEPA’s modeling for CAIR. The Technical Support Document for the final CAIR, March 2005, 

provided modeling results with and without the implementation of the CAIR. Differences between the 

USEPA’s modeling and the attainment demonstration are: 1) the meteorology was for 2001, 2) the DVB 

was the weighted design values the 1999-2003 period, and 3) the modeling results were for 2010. These 

modeling results are listed in Table L-9. 

Table L-9: Metrolina DVFs based on the USEPA’s CAIR Modeling 

DVF (ppb) County DVB 

(ppb) 2010 Base 2010 CAIR 

Lincoln 92.3 76.1 74.5 

Mecklenburg 100.3 82.5 81.4 

Rowan 99.7 81.3 80.1 

Union 87.7 71.9 71.1 

York, SC 83.3 70.0 68.5 

The USEPA’s results were for the highest monitor in a county where more than one monitor is 

located. The USEPA’s modeling results predict that the Metrolina nonattainment area should be below 

the 8-hour ozone standard by 2010. Therefore, this modeling supports weight of evidence that the 

Metrolina area will attain the 8-hour ozone standard by 2011. 

 D. Air Quality Trends and Additional Reductions in Emissions 

Since the 8-hour ozone designation for the Metrolina area, the 8-hour ozone design values have 

improved significantly. The 2001-2003 design value period had values as high as 100 ppb and six out of 

the seven North Carolina monitors in the area were violating the NAAQS. Preliminary data indicates that 

for the latest design value period, 2007-2009, the highest violating monitor, the County-Line monitor in 

Mecklenburg County, will have a value of 86 ppb and only that monitor will exceed the NAAQS (See 

Table L-10). 

Table L-10: Design Values (ppb) for the North Carolina Monitors in the Metrolina Area 

Monitoring Site County 2001-

2003 

2002-

2004 

2003-

2005 

2004-

2006 

2005-

2007 

2006-

2008 

2007-

2009 

Arrowood Mecklenburg 84 81 78 80 83 79 75 

County Line Mecklenburg 98 92 87 88 93 94 86 

Crouse Lincoln 92 86 81 79 83 82 76 

Enochville Rowan 99 91 85 85 90 88 82 

Garinger (Plaza) Mecklenburg 96 91 86 88 90 89 82 

Monroe Union 88 85 79 78 81 80 76 

Rockwell Rowan 100 94 88 83 89 88 83 

York York, SC 84 81 75 76 79 77 71 

The current ozone design values are very close to the predicted attainment year design values. The 

reduction in design values since the area was designated nonattainment is attributed to significant 

reductions in NOx emissions that have occurred. The emission reductions from the NOx SIP call occurred 

between 2004 and 2007, the initial Phase I year for CAIR is 2009, and every year the mobile source fleet 

becomes cleaner and reduces the NOx emissions from the highway and off-road mobile source sectors. 
16 

All of these reductions have contributed to the improvement of the design values. In fact, the air quality 

measurements for 2009 exhibit clean data, i.e. the fourth highest value at each monitor is below the 1997 

8-hour ozone standard. 

Continued reductions of emissions from the mobile source sector and the utility sector will influence 

the ozone formation in this region. The NCDAQ has estimated that there will be approximately 7.6 tons 

per day of NOx emissions reduced each year from the highway and off-road mobile sectors. These 

reductions are the result of federal motor vehicle and equipment engine standards for both highway 

vehicles and off-road equipment, respectively. 

Figure L-8: Location and size of the Duke Energy facilities located in the vicinity of the Metrolina 

nonattainment area. 

Additionally, the overall background levels of ozone are expected to decrease as the utilities in the 

eastern United States put on additional controls to meet CAIR as well as the reduction in emissions of 

highway and off-road mobile sources throughout the country. For North Carolina, 2009 is the final 

compliance year for the NOx emission caps for the Clean Smokestacks Act. Figure L-8 displays the 

location and size of the Duke Energy facilities located in the vicinity of the Metrolina nonattainment area. 

Table L-11 lists the units that are in and around the Metrolina area and shows the year the controls 

recently came on line and the estimated amount of NOX emissions reductions for the ozone season.

Table L-11: Utility NOx Emission Reductions since 2006 Ozone Season 

Facility County Technology Operational 

Date 

Ozone Season 

Reductions 

(tons/season) 

Allen Steam Station 

 Unit 2 Gaston SNCR Spring 2007 ~300 
17 

Facility County Technology Operational 

Date 

Ozone Season 

Reductions 

(tons/season) 

 Unit 3 SNCR Fall 2007 

Buck Steam Station 

 Units 3 & 4 

 Units 5 & 6 

Rowan Low NOx Burners 

SNCR 

Spring 2007 

Fall 2006 

~350 

Riverbend 

 Unit 4 

 Unit 5 

 Unit 6 

 Unit 7 

Gaston 

SNCR 

SNCR & Burners 

SNCR & Burners 

SNCR 

Spring 2007 

Spring 2007 

Fall 2006 

Fall 2006 

~325 

Marshall Steam Station 

 Unit 2 

 Unit 3 

 Unit 4 

Catawba SNCR 

SCR 

SNCR 

Spring 2007 

Fall 2008 

Fall 2006 

~2,300 

Total expected reduction = 3,275 tons/ozone season 

SNCR = Selective Non-Catalytic Reduction 

SCR = Selective Catalytic Reduction 

The combination of the highway and off-road mobile sources and utility NOx emission reductions 

that occurred in the Metrolina area between the end of the 2006 ozone season and before the beginning of 

the attainment year 2009 was significant. The additional NOx emission reductions in the area that 

resulted in the Metrolina area having clean data for 2009, which will allow the State to request a one-year 

extension of the attainment date. 

 E. Local Measures not Modeled 

As discussed in Section I of the attainment demonstration narrative, the Metrolina nonattainment 

area is a NOx limited area and the largest sources of NOx emissions in this region come from mobile 

sources (highway and off-road) and electric generating facilities. A significant source of NOx emission 

reductions that has not been included in the 2009 modeling is the addition of a SCR unit at Marshall Unit 

3. When the modeling was started, Duke Energy had installed a SNCR unit at Marshall Unit 3. 

However, since the expected 2009 Duke Energy system-wide NOx emissions is very close to the Clean 

Smokestack Act annual budget for this company, Duke Energy has announced that they plan to install a 

SCR unit in order to provide a safety margin in meeting the Clean Smokestack Act NOx budget. As can 

be seen in Figure L-8 in the previous section, the Marshall Steam Station is located north of and adjacent 

to the Metrolina nonattainment area. The additional NOx emission reductions expected at this facility 

caused an impact on the ozone formation in the Metrolina area on days when the winds are coming from 

the North/Northwest and on days when there is recirculation occurring. This SCR unit was installed in 

the Fall of 2008 and was operational at the beginning of 2009. The unit was modeled with the expected 

emissions reductions for the 2011 attainment year. A copy of the 2009 compliance plan for Duke Energy 

documenting the installation of the SCR at Marshall Unit 3 can be found in Appendix M. In addition to 

the Marshall NOx emission reductions, the Metrolina area has a number of groups that work towards 

decreasing emissions. These measures are voluntary measures that, although they may not account for 

large emission reductions, are directionally correct. A few of the known measures that are under way in 

the Metrolina area are listed below. 
18 

• I-77 HOV lane in Mecklenburg County. A recent evaluation of the HOV lanes on I-77 through 

Charlotte, North Carolina reported that there has been an observed increase of use of the HOV 

lanes since it has opened. It was reported that in November 2005, “...the HOV lane carried 

nearly 50 percent of the average number of persons who are traveling in a general-purpose lane in 

the morning peak hour, but in less than 20 percent of the number of vehicles.” Additionally, the 

“Average daily patronage on the CATS [Charlotte Area Transit System] express routes using the 

I-77 HOV facility increased by 63 percent between October 2004 and 2005 ...”. This reduction 

of vehicle miles traveled in this area was not modeled in the attainment demonstration. Having 

more people carpooling or using the transit system in Mecklenburg will reduce both VOC and 

NOx emissions. A copy of the North Carolina Department of Transportation (NCDOT) 

evaluation of the I-77 HOV lane can be found at the end of this Appendix. 

• Truck Stop Electrification in Rowan County. In 2006, 50 spaces at a truck stop in Rowan County 

were converted with Idle Aire technology. This technology provides truckers with electricity and 

air conditioning, allowing the truckers to turn off their engines while they rest. This results in a 

reduction of both NOx and VOC emissions. 

• Express Bus Route (Cabarrus/Rowan Counties). A new connecting service was created between 

Rider and Salisbury Transit. This provided an express route between Kannapolis and Salisbury. 

Having an express route between these two cities reduces the number of personal cars on the 

roadways, which in turn will reduce VOC and NOx emissions. This new express route became 

operational in April 2009. 

• Express Bus Route (York/Mecklenburg Counties). CATS has offered an Express Bus Route 

between Rock Hill and Charlotte since 2001. Additional service was added in 2008. 

• Pedestrian walkways and Bikeways Projects: A number of the communities are creating 

walkways and bikeways in order to provide safe pathways for pedestrians and bicyclists to move 

about busy traffic areas. These types of projects provide safe alternatives to driving in the city. 

• Idle Reduction Policies. North Carolina Department of Public Instruction has issued a policy that 

all school bus drivers are to refrain from idling their buses while waiting to pick up children at the 

school as well as when the buses are at the transportation yard. Additionally, several cities and 

businesses have issued idle reduction policies for their fleet vehicles. This reduces VOC and NOx

emissions as well as fine particulate matter. Some of the partners passing idle reduction policies 

include: Town of Concord, City of Salisbury, and Duke Power. 

• South Carolina’s Breathe Better (B2) Anti-Idling Program for Schools. Several elementary 

schools in the Rock Hill area started the B2

 program during the 2008-2009 school year. 

• Biodiesel use. A number of cities, counties and businesses have started using biodiesel for their 

diesel fleet. Most often B-20 is being used. B-20 will reduce VOC emissions as well as fine 

particulate matter. Some of the partners using biodiesel include: Gaston County Landfill, Town 

of Matthews, City of Monroe, Union County, NCDOT, and Duke Power. 

• Diesel Retrofits. A number of cities, counties and school districts have installed Diesel Oxidation 

Catalysts (DOCs) or Diesel Particulate Filters (DPFs) on their diesel equipment. The vehicles 

that have been retrofitted include schools buses, as well as county fleet trucks for solid waste 

pickup. Although these types of filters are designed to remove fine particulate matter, when used 

with ultra low sulfur diesel fuel, NOx and VOC emissions are also reduced. Some of the partners 

installing DOCs and/or DPFs include: Cabarrus County Schools, Gaston County Schools, Iredell 

County Schools, Lincoln County Schools, Mecklenburg County Schools, Rowan County Schools, 

Salisbury Public Schools, City of Charlotte and Mecklenburg County. 
19 

• Grants to Replace Aging Diesel Engines (GRADE). Mecklenburg County Air Quality has 

developed this incentive program to reduce air pollution from off-road construction equipment. 

GRADE provides incentive funding to owners of offroad construction equipment such as loaders, 

graders, bull dozers etc., who are willing to replace their aging equipment with newer less 

polluting technology. 

• Grants to Replace Aging Diesel Engines Plus (GRADE+). Mecklenburg County Air Quality 

received a grant under the American Recovery and Reinvestment Act to expand the GRADE 

program to include 13 North and South Carolina Counties and also cover on-road and stationary 

diesel engines. 

• Diesel Emissions Reduction Act (DERA). DERA provides new diesel emissions reduction grant 

authority for EPA. This funding is used to achieve significant reductions in diesel emissions that 

improve air quality and protect public health. In response to DERA, EPA created grant and 

funding programs under the National Clean Diesel Campaign (NCDC) to build on the success of 

its regulatory and voluntary efforts to reduce emissions from diesel engines. Through this effort, 

EPA is working to reduce the pollution emitted from the existing fleet by promoting a variety of 

cost-effective and innovative emission reduction strategies. 

• North Carolina Heavy-Duty Vehicle Idling Restrictions. The North Carolina Environmental 

Management Commission adopted a rule to reduce unnecessary idling of heavy-duty trucks on 

July 9, 2009. If no appeal is made for legislative review, the rule is schedule to become effective 

on September 1, 2009. This rule generally prevents any person who operates a heavy-duty 

vehicle to cause, let, permit, suffer or allow idling for a period of time in excess of five 

consecutive minutes in any 60 minute period. 

• Idling Restrictions for Commercial Diesel Vehicles. Section 56-35-10 of the Code of Laws of 

South Carolina, which became law in May 2008, stipulates that, barring certain exceptions, an 

operator of a commercial diesel vehicle may not allow the vehicle to idle for more than ten 

minutes in any sixty-minute period.

 F. Weight of Evidence Conclusions 

The SCDHEC agrees with the NCDAQ that it is better to use a five-year straight average DVB in the 

attainment test since it will normalize the effects of meteorology on design values more so than a 

weighted DVB. Based on the alternative DVF calculated in this section, all of the Metrolina 

nonattainment area monitors are predicted to be below the 8-hour ozone NAAQS in 2009 and 2011. 

Although the monitors still fall within the range for weight of evidence requirements in 2009, the monitor 

DVFs are lower than when a weighted DVB is used. 

The air quality modeling metric analyses for the Metrolina nonattainment area demonstrates relative 

reductions well beyond the recommended 80 percent mark that is considered appropriate for concluding 

that a proposed strategy would meet the 8-hour ozone NAAQS. Additionally, other air quality modeling 

studies have found that the Metrolina area should attain the 8-hour ozone NAAQS on a similar schedule 

as the air quality modeling presented throughout this attainment demonstration. 

The observed air quality trends in conjunction with further NOx emission reductions expected in the 

Metrolina area strengthens the argument that the attainment demonstration is an acceptable 

demonstration. Finally, given the variety of additional emissions reductions that were not included in the 

development of this modeling exercise, but will occur throughout the surrounding areas, it is reasonable 

to conclude that the short lived events portrayed in the future modeled year by an extremely small number 

of remaining exceeding grid cells will be below the NAAQS in 2011. 
20 

The SCDHEC and the NCDAQ agree that the weight of evidence provided in this section is strong 

evidence that the Metrolina nonattainment area will attain the 8-hour ozone NAAQS by 2011. 

IV Unmonitored Area Analysis 

The modeled attainment test does not address future air quality at locations where there is not an 

ozone monitor nearby. To guard against the possibility that air quality levels could exceed the standard in 

areas with limited monitoring, Section 3.4 of the Attainment Guidance suggests that additional review is 

necessary, particularly in nonattainment areas where the ozone monitoring network just meets or 

minimally exceeds the size of the network required. This review is intended to ensure that a control 

strategy leads to reductions in ozone at other locations that could have baseline (and future) design values 

exceeding the NAAQS were a monitor deployed there. The test is called an “unmonitored area analysis.”. 

The purpose of the analysis is to use a combination of model output and ambient data to identify areas 

that might exceed the NAAQS if monitors were located there. 

SCDHEC currently operates a network of 18 ozone monitors. Ten of these monitors were 

established as State and Local Air Monitoring Stations (SLAMS). These SLAMS monitors were selected 

based on specific monitoring objectives (background concentration, area of highest concentration, high 

population, source impact, transport, and rural impact) as required by the USEPA and siting scales 

(micro, middle, neighborhood, urban, and regional) established by the USEPA. Eight monitors are 

Special Purpose Monitors that were established by SCDHEC to obtain a better understanding of ozone in 

South Carolina. 

The adequacy of the Metrolina area ozone monitoring network is further demonstrated when plotted 

against a projected spatial field of 2009 and 2012 ozone design values. Figures L-9 and L-10 present the 

2009 and 2012 future year ozone design value modeling output from the VISTAS/ASIP State 

Collaborative effort and the location of each ozone monitor in and around North Carolina. The 2009 and 

2012 ozone design value spatial fields were created using the USEPA’s Modeled Attainment Test 

Software (MATS). It is clear from the MATS analysis that all of the regions of higher, yet attaining, 

ozone design values have numerous representative ozone monitors. There are no identified ozone 

hotspots that would require any additional monitoring considerations in the Metrolina area. 
21 

Figure L-9: Ozone Monitors and 2009 Modeled Spatial Field 

Figure L-10: Ozone Monitors and 2012 Modeled Spatial Field