Impact Area1-hour standards

SILs used to determine

• when a proposed source’s ambient impacts warrant a comprehensive (cumulative) source impact analysis

• the size of the impact area within which the air quality analysis is completed

• whether the emissions increase from a proposed new major stationary source or major modification is considered to cause or contribute to a violation of any NAAQS

Misnomer?

• Is there a 1-hour standard or is it a three year standard whose metric is the 98th or 99th percentile of the distribution of 1-hour concentrations averaged over the 3-year period?

• Can there technically be more than one violation at a receptor over a given time period under the metric for the standard?

Distribution Sums

• The sum of n distributions of any type is approximately normal

• Its mean is equal to the sum of the means of the components

• The standard deviations add like the law of cosines.

Normal Distribution

• 99% of the data is below 2.3 standard deviations above the mean

• 98% of the data is below 2.06 standard deviations above the mean

EPA Proposed 1-hour SILS

• NO2

• 1st highest daily 1-hour value averaged over 5 years• 7.52 ug/m3

• 4 ppb• 4% of the probabilistic standard

• SO2

• 1st highest daily 1-hour value averaged over 5 years• 7.8 ug/m3

• 3 ppb• 4% of the probabilistic standard

SIL as Percentage

PollutantAveraging time (hours)/SIL as % of NAAQS

Annual 24 8 3 1

SO2 1.3% 1.4%   1.9% 4.0%

PM2.5 2.0% 3.4%      

PM10 N/A 3.3%      

NO2 1.0%        4.0%CO     4.9%   5.0%

PollutantAveraging time (hours)/SIL as % of Class 2 IncrementAnnual 24 8 3 1

SO2 5.0% 5.5%   4.9%  

PM2.5 7.5% 13.3%      

PM10 5.9% 16.7%      

NO2 4.0%        CO          

Acute Exposure Guideline Levels

AEGL-1 is the airborne concentration, expressed as parts per million or milligrams per cubic meter (ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

• NO2 – 0.5 ppm (4% = 37.6 ug/m3)

• SO2 – 0.2 ppm (4% = 20.8 ug/m3)

Typical Impact Area

24-Hour<75 ug/m3

3-hour<8760 ug/m3

Annual

Possible OccurrenceOutside Historical Impact Areas

ConcentrationAveraging Period

Annual 24-hour 3-hour All1 100.00% 100.00% 100.00% 100.00%5 20.00% 100.00% 100.00% 20.00%

7.52 13.30% 66.49% 100.00% 8.84%7.8 12.82% 64.10% 100.00% 8.22%10 10.00% 50.00% 100.00% 5.00%

15 6.67% 33.33% 100.00% 2.22%

20 5.00% 25.00% 100.00% 1.25%

25 4.00% 20.00% 100.00% 0.80%

30 3.33% 16.67% 83.33% 0.46%35 2.86% 14.29% 71.43% 0.29%40 2.50% 12.50% 62.50% 0.20%45 2.22% 11.11% 55.56% 0.14%50 2.00% 10.00% 50.00% 0.10%55 1.82% 9.09% 45.45% 0.08%

60 1.67% 8.33% 41.67% 0.06%

65 1.54% 7.69% 38.46% 0.05%

70 1.43% 7.14% 35.71% 0.04%

75 1.33% 6.67% 33.33% 0.03%100 1.00% 5.00% 25.00% 0.01%110 0.91% 4.55% 22.73% 0.01%120 0.83% 4.17% 20.83% 0.01%

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Legend

CMT MAXDCONT

CMT Max 1-hour >= 25 ug/m3

All Design - Design less Cement

Increase in Design

0.000 - 7.520

7.521 - 20.020

All H8H 5yr Avg

Total Design Value

14.936370 - 141.000000

141.000001 - 430.971670

Cement H8H 5yr Avg

Project Design Value

3.804430 - 7.520000

7.520001 - 61.562920

Cement H1H 5yr Avg

SIL

5.057590 - 7.520000

7.520001 - 94.788100

Design Delta-Design MAXDCONT417.3805 7.01964 7.01964364.6826 5.83452 5.76713430.9717 7.92233 7.92233387.2199 5.79543 5.79543378.9753 5.74531 5.74531

298.807 4.19981 4.19981311.2635 3.76977 3.76977348.1109 5.66055 5.66055305.8382 4.53899 4.53899308.0739 4.37661 4.37661340.5536 4.30596 4.30596

• Evaluate maximum 1-hour emissions against:• Annual – 1 ug/m3

• 24-hour – 5 ug/m3

• 1-hour – 25 ug/m3

• If exceeded, culpability is determined by the difference in the design value with and without the project compared to EPA proposed SIL

• If not exceeded the project is considered insignificant.