National Ambient Air Quality Standards

(1) Not to be exceeded more than once per year.

(2) Final rule signed October 15, 2008. The 1978 lead standard (1.5 µg/m3 as a
quarterly average) remains in effect until one year after an area is designated for the 2008 standard,
except that in areas designated nonattainment for the 1978 standard, the 1978 standard remains in effect
until implementation plans to attain or maintain the 2008 standard are approved.

(3) The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which
is shown here for the purpose of clearer comparison to the 1-hour standard.

(4) To attain this standard, the 3-year average of the 98th percentile of the daily maximum
1-hour average at each monitor within an area must not exceed 100 ppb (effective January 22, 2010).

(5) Not to be exceeded more than once per year on average over 3 years.

(6) To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations
from single or multiple community-oriented monitors must not exceed 15.0 µg/m3.

(7) To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations
at each population-oriented monitor within an area must not exceed 35 µg/m3 (effective December
17, 2006)

(8) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour
average ozone concentrations measured at each monitor within an area over each year must not exceed 0.075
ppm. (effective May 27, 2008)