Opinion ID: 186242
Heading Depth: 3
Heading Rank: 1

Heading: HC Standard

Text: 65 The only emissions identified in § 213(a)(2) are CO, NO x , and VOCs. ISMA argues that § 213(a)(2) nevertheless refers to HC, because it mentions ozone, of which HC is a precursor, and VOCs, which consist primarily of HC. We disagree. First, ozone is not an emission, but rather an ambient pollutant formed through reactions between chemical precursors in the atmosphere, so paragraph (a)(2)'s reference to ozone is irrelevant here. Second, VOCs and HC are not coterminous. While HC and VOCs overlap in parts, they are distinct: Not all VOCs are hydrocarbons, and not all HC emissions are VOCs. See SAC at II-26, J.A. 94. It is true that EPA has in the past used HC as a surrogate for regulating VOCs, see id., but it did not do so here. Rather, EPA regulated HC emissions as a means of controlling fine PM emissions and pollution. The Agency reasonably determined that regulating HC would control PM pollution both because HC itself contributes to such pollution, and because HC provides a good proxy for regulating fine PM emissions. 67 Fed.Reg. at 68,254. Based on the foregoing, we conclude that EPA has the authority to regulate HC emissions under § 213(a)(4).