US: Researchers at Yale and Columbia Universities along with Battelle Memorial Institute used satellite data to estimate ground-level particle pollution in China. They estimated ground-level annual average concentrations of the pollutant PM 2.5 for all of China over the last decade.
PM 2.5 refers to particulate matter measuring 2.5 microns or less in diameter and has become a focus of public safety campaigners in China in recent months. Fine particulates have the ability to penetrate human lung and blood tissue and can lead to asthma, cardiovascular disease and cancer.
Scientific instruments aboard the satellites assessed the 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.
Several studies developed algorithms and models to relate the AOD measures to ground-based measurements of particulate matter. Of course, relating these atmospheric column measurements to ground-level measurements is tricky and depends on the vertical structure, composition, size, distribution and water content of the atmospheric aerosol. Therefore, regional differences and climatology also play a role in the extrapolation of PM 2.5.
According to the research conducted by US scientists, most provinces in China exceeded the WHO recommendation of PM 2.5 levels.
Source: The Guardian