Radiocarbon-derived source apportionment of fine carbonaceous aerosols before, during, and after the 2014 Asia-Pacific Economic Cooperation (APEC) summit in Beijing, China

The Asia-Pacific Economic Cooperation (APEC) summit took place in Beijing, China, 5-11 November 2014, during which numerous measures were performed to control the air pollution, and consequently, the sky of Beijing was so clean that the public called it "APEC blue." The concentrations before, during, and after the APEC summit are 14.4+/-6.81 mu g C/m(3), 6.66+/-2.99 mu g C/m3, and 32.3+/-10.6 mu g C/m(3), respectively, for organic carbon (OC), and 2.27+/-1.17 mu g C/m(3), 0.76+/-0.52 mu g C/m(3), and 4.99+/-1.74 mu g C/m(3), respectively, for elemental carbon (EC). We quantify the contributions of fossil and nonfossil sources to the OC and EC using radiocarbon. Results show that the contribution of nonfossil sources is 56+/-1% (before APEC), 61+/-1% (during APEC), and 48+/-1% (after APEC), respectively, for OC, and 36+/-4% (before APEC), 46+/-1% (during APEC), and 33+/-4% (after APEC), respectively, for EC. Comparing to the period before APEC, 70% and 60% of fossil EC and OC and 60% and 50% of nonfossil EC and OC are reduced, respectively, implying that the control on the nonfossil sources has considerable contribution to the good air quality in Beijing. Both EC and OC mass loadings during the APEC summit would have increased by 60% if the biomass-burning activities were not taken into account for control. In such a case, the atmospheric visibility would decrease 20% at least and the blue sky thereby would likely not have been visible during the summit.