Man-made and visible from space

“PM2.5” seems an odd and wonky 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 that rated as PM10. Yet until recently China’s authorities have revealed measurements only for PM10. When people realised this, an online revolt broke out. Such was the public pressure that authorities caved in, and PM2.5 data are now being published for Beijing and a handful of other cities.

What of 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, and estimating from those 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.

Read More at The Economist