Under the Clean Air Act, the U.S. Environmental Protection
Agency (EPA) publishes National Ambient Air Quality Standards
(NAAQS) for important air pollutants. Each state must then adopt
a State Implementation Plan (SIP) providing for the implementation,
maintenance, and enforcement of the NAAQS. The SIP is submitted
to the EPA for approval. If the SIP is found deficient, the
EPA may apply a federal implementation plan in its place. Even
if a SIP is approved, the EPA may call for revisions as necessary
if the SIP no longer complies with the law.
EPA reviews NAAQS periodically to determine whether the standards
are adequately protecting public health. In 1997, the EPA determined
that the ozone standard was inadequate and set a more stringent
standard.
Every state monitors ozone. When a state exceeds the NAAQS,
it is in nonattainment. Northeastern states had high levels
of ozone in summer and were in nonattainment. These states claimed
their ozone problem was due in part to upwind states releasing
ozone-forming pollutants that contributed significantly to ozone
problems in downwind states.
Through extensive computer modeling of air transport processes,
it was determined that Indiana contributed at least two parts
per billion (ppb) or four percent of the ozone exceedances in
New York City. Therefore, the EPA ordered Indiana and 18 other
eastern states to revise their SIPs to improve air quality within
the state and reduce interstate transport of ozone.
Specifically, EPA required that each state reduce emissions
of nitrogen oxides (NOx--precursors of ozone),
in what is known as the NOx SIP call. Indiana must
reduce allowed NOx levels 36 percent by 2007. The Indiana
Department of Environmental Management (IDEM) is the agency
charged to write the Indiana SIP for NOx.
