ProPublica: “For decades, noxious, cancer-causing gases poured from some of the nation’s largest industrial polluters, seeping invisibly from cracks in antiquated pipes or billowing out of smokestacks in plumes that choked the communities nearby. And for decades, the Environmental Protection Agency tracked those emissions not by monitoring the air but by relying on a kind of honor system. Companies were allowed to estimate their chemical pollution using methods that even the EPA conceded were often unreliable. In 2023, the EPA received irrefutable proof that these estimates were highly flawed. The agency had required 20 industrial facilities to temporarily install air monitors around their perimeters — known as fence-line monitoring — to see how bad the pollution actually was. The results, compiled now for the first time by ProPublica, were shocking. In virtually every case, the actual emissions were higher — often much higher — than the estimates, ProPublica found. At one steel industry plant near Pittsburgh, a potent carcinogen was found at levels more than 30 times higher than estimated. In Louisiana, a chemical facility recorded levels of another toxic chemical that were 156 times higher. Despite industry opposition, the EPA took action last year. More than 130 industrial facilities would have to install permanent air monitors, starting as soon as this year. Communities surrounding some of the country’s most notorious polluters would finally get a glimpse of what they were breathing. The monitors would act as a warning system: If pollution levels were to exceed new standards set by the EPA, the facility would have to find the source of the leaks and fix them. In fact, among the 20 plants that were forced to conduct temporary monitoring, half would have violated these standards, ProPublica found.