Characteristics and source apportionment of organic matter in PM(2.5) from cities in different climatic zones of China.

摘要

For the first time, the dependency of the characteristics of organic matter in PM2.5 on geographical and climatic zones in three metropolitan cities of China was studied. Seasonal samples were collected at suburban and urban sites in Beijing, Shanghai and Guangzhou in 2002 and 2003. To further support the above study, seasonal samples were also collected at Changdao Island, a remote island, in Bohai Sea/Yellow Sea. Concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and solvent-extractable organic compounds (SEOC) were analyzed. The characteristics of the n-alkanes, polycyclic aromatic hydrocarbons, n-fatty acids, n-alkanols and molecular markers such as triterpanes were determined and used for source identification. Source apportionment was complemented by Chemical Mass Balance (CMB) modeling using the measured organic species as tracers. The impact of wind speed and wind direction on air quality was studied by back trajectory calculations and analysis.; In general, traffic emissions were the largest contributors of OC followed by coal burning, kitchen emissions, vegetative detritus and biomass burning. However, in the space-heating season in Northern China, coal burning was the most important contributor of OC in the suburban areas of Beijing and at Changdao.; Beijing had the highest concentration of organic aerosol followed by Guangzhou and Shanghai, while seasonal variation was in reverse order. Dispersion conditions determined by local topographies and meteorology were responsible for this trend. Contrary to common understanding, pollutant concentrations at the suburban sites were higher than the urban sites in all three cities. The main reason was the rapid urbanization of the suburban areas in the immediate vicinity of urban centers since China opened up for economic development, in addition, large numbers of manufacturing plants were relocated from the cities to the countryside in an attempt to clean up the urban environment.; WSOC/TC ratios were comparable in all three cities at 0.2-0.3 and this value can be considered typical for urban aerosols from Chinese cities. Similar PAH/ALK ratios were found in the three cities, and PAHs were from a mixed contribution of coal burning and engine exhaust. More than half of the resolved SEOC was found to be n-fatty acids and they were mainly from kitchen emissions based on source profile comparisons and CMB analysis. The increase of contribution from coal burning in Beijing due to space heating was identified by the different distribution of triterpanes in summer and winter.; The relative concentrations of semivolatile fossil fuel residue n-alkanes (=C26) were inversely dependent on the ambient temperature. Similar trend was found in the concentrations of the semivolatile PAHs (molecular weight =228). This was mainly caused by the gas/particle partitioning of semivolatile species in the different climatic zones. The enrichment of higher molecular weight plant wax compounds from Beijing to Shanghai to Guangzhou was a reflection of the variations of the vegetation in the different climatic zones.; The seasonal variations in the concentrations and compositions of organic matter at Changdao were similar to the three cities, especially to Beijing. The remote island was also impacted by anthropogenic pollutants, and transported particles played a significant role in the contribution of the organic matter exemplified by the high WSOC/TC, low C18:1/C18 fatty acid, and high BeP/(BeP+BaP) ratios.