14C-Based source assessment of carbonaceous aerosols at a rural site

Radiocarbon (14C) has become a powerful tracer in source apportionments of atmospheric carbonaceous particles. Fine particles (PM2.5) were collected at a rural site of Beijing in the summer and winter of 2007. The fractions of contemporary carbon (fC) in total carbon (TC) and elemental carbon (EC) are presented using 14C measurements. This value directly represents the contemporary biogenic contribution, since recently living biomass and biogenic organic compound emissions have fC = 1, whereas anthropogenic emissions from fossil carbon have fC = 0 because the 14C in the latter has completely decayed. The measured fC (TC) values range from 0.30 to 0.38 (n = 12) in winter and 0.31 to 0.44 (n = 12) in summer, respectively. The levels of fC values are lower than those from other rural sites in the world, indicating that the Yufa site was heavily influenced by anthropogenic emissions. The high TC concentrations in winter with the lower average fC (TC) suggest that coal burning for residential heating was significant contributors to the TC concentrations. The sources of contemporary carbon are primary emissions due to biomass burning, and biogenic secondary organic aerosol. Biomass burning was a dominant contributor in the winter. Fossil fuels represented 80–87% of EC in both seasons.