The United States has some of the cleanest air in the world, at least when it comes to actual dangerous smog, PM10 – particulate matter 10 microns in size. It is a clear killer, at one point leading to the deaths of over 10,000 in London during a weather anomaly that caused it to stay low.
By the 1990s, PM10 had been drastically reduced in developed countries and air activists began to ‘define pollution down.’ If they want air quality maps to be red or orange they knew the solution was to target smaller particles, so they settled on PM2.5. At 25 percent the size of the known killer, there is four times as much of it. Virtually no place could always be green, so over 40 states in America with better quality than the remote forests of Siberia could still have clueless meteorologists…
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