"Pm2.5" seems an odd and wonkish 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 212 microns across. Such dust can get deep into people's lungs; far deeper than that rated as pmio. Yet until recently China's authorities have revealed measurements only for pmio. When people realised this, an online revolt broke out. Such was the public pressure that the government caved in and PM2.5 data are now being published for Beijing and a handful of other cities.
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