Particle-based ambient air pollution causes more than 4 million premature deaths each year globally, according to the World Health Organization. The tiniest particles—2.5 microns or smaller, known as PM2.5—pose the greatest health risk because they can travel deep into the lungs and may even get into the bloodstream.
Although total PM2.5 levels have decreased 42 percent in the U.S. since 2000 as a result of clean air regulations, scientists are concerned about the health impacts of even low levels of such pollution. The U.S. Environmental Protection Agency lowered the annual national air quality standard for PM2.5 from 12 to nine micrograms per cubic meter (µg/m3) this week. EPA administrator Michael Regan said in a press conference that officials estimate the new standard will save up to $46 billion dollars in avoided health care and hospitalization costs by 2032. “Health benefits will include up to 800,000 avoided cases of asthma symptoms, 4,500 avoided premature deaths, and 290,000 avoided lost workdays,” he said. The World Health Organization adopted an even lower 5 µg/m3 standard in 2021, citing the growing evidence of deadly harm.
Beyond investigating their size, scientists are also digging into the chemistry of airborne particles, which, unlike other regulated pollutants such as lead and ozone, encompass a wide array of solid and liquid particles from soot to nitrate. Some airborne particles are directly emitted from car tailpipes or industrial sources; others form in the atmosphere. And the balance of those is shifting. To help states meet the tougher air standards, scientists will need more detailed studies of particle sources.
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