Shortly before Christmas in 1969 a dense fog rolled in across the bayous of the Texas Gulf Coast. For more than four days it blanketed a vast region, as far west as San Antonio and as far east as Port Arthur. Flights were grounded, cars crashed, and all traffic halted in the Houston Ship Channel, one of the busiest ports in the world. The murk posed a real threat to Texans with emphysema or asthma, to the elderly or the infirm. “These people are going to suffer more acutely,” a local physician told the Houston Post . Indeed, one Houston hospital reported a 240 percent surge in patients with breathing issues; a health officer noted a “tremendous increase” in upper respiratory symptoms. To many Texans the source of the haze was, ironically, clear. It was “pollution-fed fog,” as the Post put it in a front-page headline, a glaring manifestation of a problem that plagued the industrialized parts of the region.…