Chemical and optical characteristics of atmospheric aerosols in Beijing during the Asia-Pacific Economic Cooperation China 2014

To evaluate the effectiveness of regional pollution control measures for improving visibility imposed during the Asia-Pacific Economic Cooperation (APEC) period, day- and nighttime PM2.5 and PM10 samples were collected at an urban site in Beijing from October to November, 2014. PM2.5 and PM10 samples were subject to chemical analysis for major water-soluble ions, organic carbon (OC), element carbon (EC), and biomass burning tracers - anhydrosugar levoglucosan (LG). In addition, aerosol scattering coefficient (bsp) and aerosol absorption coefficient (bap) at dry condition were measured. PM2.5 mass concentration was 190 ± 125, 88 ± 60, 199 ± 142 μg m−3 during the pre-, during- and post-APEC period, respectively, while the concentration of the sum of (NH4)2SO4 and NH4NO3 was 75 ± 69, 19 ± 22 and 40 ± 46 μg m−3, respectively. The sum of (NH4)2SO4 and NH4NO3 accounted for 49 ± 24%, 19 ± 12% and 24 ± 12% of bext (the sum of bsp and bap) at ambient condition during the pre-, during- and post-APEC period, respectively, and the corresponding numbers are 39 ± 18%, 62 ± 8% and 61 ± 10% for the sum of OM and EC. Reduction of secondary inorganic aerosols played a key role in the “APEC blue”, especially under moisture conditions due to their hygroscopic properties. As a result, visibility was improved significantly during the APEC period with five out of the 12 days having a visibility higher than 20 km. Control of biomass burning, especially during the nighttime, was not performed well during the APEC period, which should be paid more attention in making future emission control measures.