Identification and estimate of biomass burning contribution to the urban aerosol organic carbon concentrations in Beijing

摘要

Daily participate matter samples were collected during 1 year from 7 November 1997 to 31 October 1998 in Beijing area, at two monitoring sites, the Ming Tomb (a background site) situated northernmost of the basin and the Temple of Heaven (a residential site) inside the city. For 110 atmospheric aerosol samples organic carbon (OC) was determined with a two-step thermal procedure using a CHN elemental analyzer, and water-soluble potassium (K~+) with flame atomic absorption spectrometry. The annual average of OC and K~+ concentrations of the Ming Tomb site were 22.0 μg Cm~(-3) and 1.21 μg m~(-3), respectively, while that of the Temple Heaven site were 41.5 μg C m~(-3) and 1.94 μg m~(-3). At the Ming Tomb site the monthly average of K~+ concentration appeared the highest in June (3.07 μg m~(-3)), three times as much as that in May (1.02 μg m~(-3)). At the Temple Heaven site, the highest value was also in June (4.22 μg m~(-3) while 1.97 μg m~(-3) in May). Regression analysis results showed that at both sites the OC/K~+ concentration ratio value is what expected for biomass burning. Our results thus suggest that biomass burning influence is on a regional scale. It was calculated as an upper estimate, that at Ming Tomb site about 50%, 70%, and 46% of the OC concentrations in May, June, and July, respectively, were attributed to biomass burning while at the more urban site of Temple of Heaven, the biomass burning OC contribution is still high (32%, 43%, and 10% respectively). In the case of a severe pollution event in June 2000 in Beijing, it has been shown that temperature inversion and wind direction aggravated substantially air pollution caused by biomass burning. Our work suggests that biomass burning in the Beijing region is a significant repetitive pollution factor that cannot be neglected.