Ozone Formation
When NOx and volatile organic compounds
(VOCs) enter the atmosphere, they react in the
presence of sunlight to form ground-level
ozone, which is a major ingredient of smog.
The revised NAAQS for ozone is 0.08 ppm
(eight-hour average). Many urban areas do not
meet this standard and are classified as
nonattainment, and a large number of power
plants are situated within these nonattainment
areas. Nonattainment status is attributable not
only to locally released NOx emissions but also
to significant amounts of ozone and ozone precursors
(NOx and VOCs) transported by wind
over a wide geographical region.
To address regional pollutant transport,
EPA has issued a rule under Title I of the
CAAA governing NOx emissions from electric
power plants and other large stationary boilers
in an area consisting of 22 Eastern states and the
District of Columbia. To meet the ground-level
ozone NAAQS in that area, EPA projects an
average NOx emissions rate for electric power
plants of 0.15 lb/million Btu during the fivemonth
(May through September) “summer”
ozone season.