§7473 Increments and ceilings

Summary

State air-quality plans must set rules so sulfur dioxide and particulate matter do not rise above allowed increases over the baseline or above set concentration limits. Shorter-term increases tied to national ambient air quality standards (anything other than an annual average) may be exceeded only once per year. The allowed increases over baseline depend on the area's class: Class I — particulate: annual geometric mean 5 micrograms per cubic meter, 24‑hour 10; sulfur dioxide: annual arithmetic mean 2, 24‑hour 5, 3‑hour 25. Class II — particulate: annual 19, 24‑hour 37; sulfur dioxide: annual 20, 24‑hour 91, 3‑hour 512. Class III — particulate: annual 37, 24‑hour 75; sulfur dioxide: annual 40, 24‑hour 182, 3‑hour 700. Also, for each exposure period the total concentration of any pollutant cannot be higher than the concentration allowed by the national primary or national secondary ambient air quality standard for that period. After public notice and a hearing, a Governor may adopt orders or rules that exclude certain increases when checking compliance. These exclusions can cover increases from stationary sources that switched fuels because of a federal order (sections 792(a) and (b) of title 15), increases from stations that switched because of a natural gas curtailment plan under the Federal Power Act, particulate increases from construction or other temporary activities, and increases from new sources outside the United States compared with the baseline. Exclusions for the fuel-switching or gas‑curtailment items cannot be used more than five years after the federal order or plan took effect (if both apply, five years after the later date). Any such exclusion only takes effect after the Governor sends the order or rule to the Administrator and the Administrator finds it complies with these rules.