Characteristics and sources of PM in seasonal perspective e A case study from one year continuously sampling in Beijing

Özet

Daily mass concentrations and chemical compositions (elemental carbon, organic carbon, water solubleions, chemical elements and organic species) of PM were measured continuously in Beijing for one yearfrom June 2010 to June 2011 (365 samples). The seasonal variation of PM mass concentration followedthe order of spring 2011 > winter 2010 > summer 2010 > autumn 2010. Organic matter (OM) andsecondary inorganic aerosol components (SNA: SO42, NO3 and NH4þ) were the two major fractions of PMduring the whole year. Source apportionment by PMF performed on the basis of a full year of data,including both inorganic and organic species, showed that biomass burning, secondary sulfate and nitrateformation, mineral dust, industry, coal combustion and traffic were the main sources of PM inBeijing during 2010e2011. Specifically, comparison among the four seasons shows that the contributionof secondary sulfate and biomass burning, secondary nitrate formation, mineral dust, and coal combustionwere the dominating sources of PM in summer, autumn, spring and winter, respectively. Thecontributions of industry to PM was distributed evenly in four seasons, while traffic contributed more insummer and autumn than in winter and spring. Backward trajectory analysis was applied in combinationwith PMF and showed that air flow from the South contributed mostly to high PM mass concentrations inBeijing. Meteorological parameters (temperature, wind speed, wind direction, precipitation and mixinglayer height) influence such a variation. In general, high relative humidity and low mixing layer heightcan raise PM mass concentration, while high wind speed and precipitation can reduce pollutants. Inaddition, wind direction also plays a key role in influencing PM because different wind directions canbring different pollutants to Beijing from different regions.