Seasonal characteristics of biomass burning contribution to Beijing aerosol

110 atmospheric aerosol samples collected from November 1997 to October 1998 at two monitoring sites (Ming Tomb and Temple Heaven) in Beijing were analyzed for the con-centration of organic carbon (OC) and water-soluble potassium (K+). Four biomass burning epi-sodes, namely spring farming, summer harvesting, autumn harvesting and leaf falling were iden-tified using the tracer of K+. Biomass burning contribution to the urban aerosol OC concentration in Beijing was estimated by regression analysis of OC and K+ concentration data. The slopes of regression analysis are similar at the two monitoring sites, presenting regional characteristics. Severe air pollution event occurred during autumn harvesting period in 1998 with substantial secondary OC formed, in which biomass burning was one of the major emission sources. Bio-mass burning is a prominent source of aerosol OC in Beijing and is featured by its seasonality and periodicity. It may contribute as much as 30 to 60 percent of the total OC in typical cases.