TABLE 2-1 National Ambient Air Quality Standards

Pollutant or Indicator

Averaging Times

Primary Standard

Secondary Standard

Carbon monoxide (CO)

8 hra

9 ppm (10 mg/m3)

None

 

1 hra

35 ppm (40 mg/m3)

None

Lead (Pb)

Quarter (average)

1.5 µg/m3

Same as primary

Nitrogen dioxide (NO2)

Year (average)

0.053 ppm (100 µg/m3)

Same as primary

Particulate matter < 10 µm in aerodynamic diameter (PM10)f

Year (average)b

50 µg/m3

Same as primary

24 hra

150 µg/m3

Same as primary

Particulate matter < 2.5 µm in aerodynamic diameter (PM2.5)f

Year (average)c

15 µg/m3

Same as primary

24 hrd

65 µg/m3

Same as primary

Ozone (O3

)8 hre

0.08 ppm

Same as primary

Sulfur oxides (SOx)

Year (average)

0.03 ppm

 

24 hra

0.14 ppm

 

3 hra

0.5 ppm (1,300 µg/m3)

aNot to be exceeded more than once per calendar year.

bTo attain this standard, the expected annual average PM10 concentration at each monitor in an area must not exceed 50 µg/m3.

cTo attain this standard, the 3-year average of the annual average PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15 µg/m3.

dTo attain this standard, the 3-year average of the 98th percentile of 24-hr concentrations at each population-oriented monitor in an area must not exceed 65 µg/m3.

eTo attain this standard, the 3-year average of the fourth-highest daily maximal 8-hr average O3 concentrations measured at each monitor in an area over each year must not exceed 0.08 ppm.

fEPA has recently proposed to revise these standards (see 71 Fed. Reg. 2620 [2006]).

SOURCE: EPA 2004a.

The CAA defines a modification as “any physical change, or change in the method of operation of a stationary source” that significantly “increases” its emissions of air pollution (CAA §111(a)(4), 42 USC § 7411(a)(4)).1 That definition applies to both the PSD (CAA §169(2)(C), 42 USC § 7479(2)(C)) and Part D NSR (CAA § 171(4), 42 USC § 7501(4)) programs. The definition covers not only the addition of new emission points to existing sources

1

The CAA does not expressly exempt even very small increases in emissions. But EPA, with court approval, has exempted nonsignificant increases from NSR. Significance levels are set out in Box 2-1. Use of the term “physical change” in the rest of this report also includes a change in the method of operation of a stationary source.



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