Residents of Texas living downwind of coal-fired power plants would be far better off today if regulators had focused on cutting particle-forming SO2 emissions rather than concentrating so keenly on ozone-causing emissions, according to a recent study conducted by researchers at Rice University in Houston, Texas.

The head of the study, environmental engineer Daniel Cohan, said particulate matter, including fine inhalable particles with diameters that are generally 2.5 micrometers and smaller (PM2.5), is the deadliest of air pollutants. The finding that particulate matter imposes the greatest impact on human health is consistent with at least two other studies, the report says.

“[I]t’s not just causing deaths in the way that you might think,” Cohan said in a press release. “It’s not only by respiratory diseases, but it’s also causing increases in rates of heart attacks and strokes. These particles are small enough to pass through the alveoli and enter the bloodstream. That lets them cause damage on all aspects of our bodily systems.”

The study, which appears in the Journal of the Air & Waste Management Association, analyzed models that measure the effects of emissions from 13 coal plants in Texas. The state has historically led the nation in emissions of SO2, NOx, and CO2 from power plants, emitting more than twice as much SO2 as second-ranked Missouri in 2016. “Texas has more unscrubbed coal plants than anywhere in the country,” Cohan said. However, three of the plants were retired in 2018 and others are expected to close for economic reasons in coming years.

Meanwhile, Cohan’s team suggested that the state missed an opportunity to benefit from the Obama-era regional haze plan. The Regional Haze Rule would have cut emissions of SO2, and thus PM2.5, at eight of the highest-emitting plants in Texas. Instead, the Scott Pruitt-led Environmental Protection Agency replaced the plan with a cap-and-trade program. However, the cap-and-trade scheme set the cap higher than emissions in recent years, which allowed several power plants to continue operating unscrubbed.

“That doesn’t mean the plants will get worse,” Cohan said. “It just means the plants that should have been forced to clean up or close down have gotten a get-out-of-jail-free card.” He said the key message of the paper is that delay has very real costs for the people of Texas.

Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).