(state (IN) granted permits to defendant, a fuel-grade ethanol production facility; permits did not classify defendant as "chemical process plant" (as defendant had been classified in past) that would be limited to emission of 100 tons of certain air pollutants per year; lack of such classification would circumvent federal air pollution restrictions by allowing emission of up to 250 tons of certain air pollutants annually; issue is whether state could exclude fuel-grade ethanol production plants from category of "chemical process plants" without EPA approval of modification to IN state implementation plan (SIP); under Clean Air Act, air quality in certain areas cannot significantly deteriorate and SIP applies in such areas; defendant located in such area and is a "major emitting facility" under CAA; while state law had been modified to provide that ethanol plants were not "chemical process plants," the IN SIP through which the state implements the CAA was not modified; any modification to the IN SIP requires EPA approval; case points out irony of ethanol industry seeking special exemptions from federal air pollution rules while it claims to benefit air quality).