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For more than a decade, the United States dramatically reduced its national smog levels, but since 2015 smoke from increasingly larger wildfires is reversing that clean-up trend and making the air dirtier and deadlier, a new study finds.
Scientists say climate change deserves much, but not all, of the blame.
The national smog level dropped by 11% from 2003 to 2015 as strict federal regulations on power plants, cars and diesel engines kicked in. But since then, as wildfires have grown, the nation's average ground level ozone -- which is smog -- increased by 4%. That means if smoke increases at the current rate, smog will go back up to 2003 levels in 20 years, said study lead author Weizhi Deng, an atmospheric scientist at the University of Iowa.
Thursday's study in the journal Science also estimated an increase in deaths from ozone attacking lungs, using previously established epidemiology studies that compared death rates in clean and dirty air. They calculated an increase of 318 American deaths per year since 2013.
"For the last 20 years, by regulations, we keep decreasing the emissions" for human-caused smog-inducing chemicals, said study co-author Meng Zhou, a University of Iowa wildfire researcher. "However, because of wildfires, that is actually from natural hazards, all those kinds of effort were wiped out."
The study was novel in the way it estimated the national smog level, compensating for how the U.S. Environmental Protection Agency has a limited number of smog monitors. Those cover only 2% of the nation, mostly in urban areas. So Deng and his colleagues used those observations -- along with satellite, pollution and weather data and models -- then used artificial intelligence to create a nationwide data set of ozone levels showing smog count at a resolution slightly higher than half a mile.
EPA figures show the national ozone level since 2015 has vacillated around the same mark, going up and down a few percentage points, but Deng said, "by considering everywhere in the U.S., we actually found an increase in ozone starting from 2015."
The method using artificial intelligence is solid because it starts with "massive and reliable datasets," then uses computer models to fill in the gaps in a sensible way to make an "exceptional" high-resolution picture, said University of Delaware environment professor Cristina Archer, who wasn't part of the study.
Megafire Action's research director and senior policy advisor Teresa Feo said "experts have long called for expanding the air pollution monitoring network to improve research on wildfire smoke exposure and provide the data needed to better protect public health."