The Economist: Pollution in China, Visible from Space!

"PM2.5" seems an odd term for the blogosphere to take up, but that is precisely what has happened in China in recent weeks. It refers to the smallest solid particles in the atmosphere, those less than 2.5 microns across. Such dust can get deep into people's lungs, far deeper than rated as PM10. Yet until recently China's authorities have revealed measurements only for PM10. When people realized this, an online revolt broke out. Such was the public pressure that authorities caved in, and PM2.5 data are noe being published for Beijing and a handful of other cities. What about the rest of China? At the moment, only PM10 data are available, but the government's hand may soon be forced here too. Though pollution data are best collected near the ground, a plausible estimate may be made from the vantage point of a satellite by measuring how much light is blocked by particles' chemical composition the likely distribution of their sizes, and a report prepared for The Economist by a team led by Angel Hsu of Yale University does just that, drawing on data from American satellites to map out PM2.5 pollution across the entire country. World Health Organization guidelines suggest that PM2.5 levels above ten micrograms per cubic meter are unsafe.