Identification and estimation of the biomass burning contribution to Beijing aerosol using levoglucosan as a molecular marker

Two series of size-selective aerosol samples, PM2.5 and PM10, were collected in Beijing from July 2002 to July 2003. The samples were analyzed for levoglucosan and related saccharidic compounds, organic and elemental carbon, and ionic species. Levoglucosan and related saccharidic compounds were mostly present in the fine size fraction. The contribution from biomass burning to the carbonaceous aerosol in Beijing was estimated; biomass burning was responsible for 18–38% of the PM2.5 organic carbon and for 14–32% of the PM10 organic carbon. The biomass burning marker levoglucosan was present all year round in Beijing. High levoglucosan concentrations in October and November were attributed to corn field burning and burning of fallen leaves, while the high level observed on 7 May 2003 was tracked back to a boreal forest fire more than 1000 km away in northeastern China. The biomass burning contribution to the Beijing aerosol is made up of two parts, a background component, which is due to biofuel burning all year round in the neighboring countryside households, and a superimposed component from seasonal crop burning events and wild fires.