Billionaire William Koch’s industrial plant in Port Arthur, Texas, is small compared to the three sprawling oil refineries that surround it – just 112 acres compared with the 10,000 acres occupied by Motiva, Valero and Total. But Koch’s Oxbow facility towers over its neighbors in one respect. It produces 10 times as much lung-damaging sulfur dioxide, SO2, as the three refineries combined. And it does so legally because of a quirk in the 1970 Clean Air Act.