Biomass burning contribution to Beijing aerosol
Biomass burning, the largest global source of el-emental carbon (EC) and primary organic carbon (OC), is strongly associated with many subjects of great scientific concern, such as secondary organic aerosol and brown car-bon which exert important effects on the environment and on climate in particular. This study investigated the relation-ships between levoglucosan and other biomass burning trac-ers (i.e., water soluble potassium and mannosan) based on both ambient samples collected in Beijing and source sam-ples. Compared with North America and Europe, Beijing was characterized by high ambient levoglucosan concentrations and low winter to summer ratios of levoglucosan, indicating significant impact of biomass burning activities throughout the year in Beijing. Comparison of levoglucosan and water soluble potassium (K +) levels suggested that it was accept-able to use K + as a biomass burning tracer during summer in Beijing, while the contribution of fireworks to K + could be significant during winter. Moreover, the levoglucosan to K + ratio was found to be lower during the typical summer period (0.21 ± 0.16) compared with the typical winter period (0.51 ± 0.15). Levoglucosan correlated strongly with man-nosan (R 2 = 0.97) throughout the winter and the levoglu-cosan to mannosan ratio averaged 9.49 ± 1.63, whereas lev-oglucosan and mannosan exhibited relatively weak correla-tion (R 2 = 0.73) during the typical summer period when the levoglucosan to mannosan ratio averaged 12.65 ± 3.38. Re-sults from positive matrix factorization (PMF) model analy-sis showed that about 50 % of the OC and EC in Beijing were associated with biomass burning processes. In addition, a new source identification method was developed based on the comparison of the levoglucosan to K + ratio and the levoglu-cosan to mannosan ratio among different types of biomass. Using this method, the major source of biomass burning aerosol in Beijing was suggested to be the combustion of crop residuals, while the contribution from softwood burn-ing was also non-negligible, especially in winter.