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Major air pollution episode right now across US

Right here, it isn't too hot. But looking at the weather across the country, damn. The heat wave is beastly to be sure, but Dr. Jeff Masters is calling it worse than that on his always fantastic blog.

"What may be the most deadly weather event to affect the U.S. this year is underway across large portions of the central and eastern U.S. A large area of high pressure with light winds has settled over the region, bringing unhealthful levels of ozone and fine particulate matter to many major cities. High pressure systems are regions where the air gradually sinks, warming as it approaches the surface. This warming, sinking air creates a layer of air aloft (typically near 3000 feet in altitude) that is warmer than the air beneath it. This "upper air inversion" acts as a lid on the atmosphere, keeping pollutants trapped near the surface. Updrafts carrying surface air into the inversion suddenly encounter air that is warmer and less dense, so the updraft dies and the pollutants that they were trying to carry aloft settle back down towards the surface. If the high pressure region is large, an extensive area of light winds at the surface will exist, keeping the pollutants trapped under the inversion from being blown away horizontally. If the high pressure system stays in place for several days, pollutants will accumulate day by day, reaching levels harmful to human health and triggering a sharp rise in the death rate. "Particulate matter," also known as particle pollution or PM, is the pollutant that causes the largest rise in the death rate. Particulate matter less than 2.5 microns in diameter (PM 2.5) is particularly harmful to the lungs. A double-whammy dose of ozone pollution is also occurring this week, since temperatures are warm enough to drive the chemical reactions that form ozone."
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