If you're wondering whether to trust the Environmental Protection Agency on mercury, ozone, climate change or other regulatory actions, you need look no further than how it has handled particulates.
EPA whitewashed the toxic flashflood it caused in Colorado. But it says particulate matter smaller than 10 microns (PM10) is risky and worries incessantly about 2.5-micron particles. (A human hair is 50-70 microns; dust, pollen and mold are around 10; combustion exhaust particles are 2.5 microns or smaller.)