Quantitative relationship between visibility and mass concentration of PM2.5 in Beijing

The pollution of particulate matter less than 2.5 mm(PM2.5) is a serio us environmental problem in Beijing. The annual average concentration of PM2.5 i n 2001 from seasonal monitor results was more than 6 times that of the U.S. nati onal ambient air quality standards proposed by U.S. EPA. The major contributors to mass of PM2.5 were organics, crustal elements and sulfate. The chemical compo sition of PM2.5 varied largely with season, but was similar at different monitor stations in the same season. The fine particles (PM2.5) cause atmospheric visib ility deterioration through light extinction. The mass concentrations of PM2.5 w ere anti-correlated to the visibility, the best fits between atmospheric visibil ity and the mass concentrations of PM2.5 were somehow different: power in spring , exponential in summer, logarithmic in autumn, power or exponential in winter. As in each season the meteorological parameters such as air temperature and rela tive humidity change from day to day, probably the reason of above correlations between PM2.5 and visibility obtained at different seasons come from the differe nces in chemical compositions of PM2.5.