The tweeting @BeijingAir pollution monitor atop the US Embassy in Beijing has long been a thorn in the government’s side, its PM2.5 measurements causing first “confusion” and “undesirable social consequences”, and later a grudging about-turn by the official monitors. At chinadialogue, Angel Hsu describes another American effort to track PM2.5 levels in China which casts a much broader gaze from a much higher vantage point.
The Great Wall may not, after all, be visible from space – but Chinese air pollution is.
How are the satellite measures of PM 2.5 derived? In short, scientific instruments aboard the satellites assess something called Aerosol Optical Depth (AOD). This is a measure of the degree to which aerosol particles prevent the transmission of light either through absorption or scattering ….
The figures … reveal telling trends for PM 2.5 data in China. All but four provinces (excluding Taiwan) have average annual exposures to PM 2.5 above levels recommended by the World Health Organization (WHO). Figure 1, below, shows a map of population-weighted fine particulate matter concentrations in China’s 31 provinces in 2007. Most provinces exceed the WHO recommendation for PM 2.5 levels, which is set at an annual average of 10 micrograms per cubic metre.