Effectiveness of temporary control measures for lowering PM2.5 pollution in Beijing and the implications.

In order to investigate the effects of the temporary strengthening of air quality assurance controlling measures during the Beijing 2015 IAAF World Championships and the Military Parade Assurance Period (MPAP) in China, we collected daily PM 2.5 aerosol samples at three typical sites (urban downtown, suburban and rural background area, respectively) in Beijing and investigated the variations of concentration of the water-soluble ions, elemental constituents, organic carbon (OC) and elemental carbon (EC) in PM 2.5 from Aug.15 to Sept.10, 2015. Simultaneously, 1-h high-resolution continuous monitoring results of PM 2.5 mass concentration as well as the chemical components which were measured at another online monitoring urban site were incorporated. The concentrations of PM 2.5 and other gaseous pollutants (SO 2 , NO 2 and CO) during the parade control period (Aug.20-Sept.3) exhibited a substantially decrease compared with the concentrations during both the non-control (August 15 to August 19 and September 4 to September 10) period and the same period in 2014. According to the CMC results, the major components were identified as secondary inorganic aerosol (SIA, the combination of sulfate, ammonium and nitrate), mineral dust and particular organic matter (POM), which together accounted for more than 80% of PM 2.5 in urban and suburban sites. POM is found to account for the largest proportion, and the obviously higher proportion of POM in the urban area revealed the significance contribution from vehicles. Compared with the non-control period, the mass concentrations of SIA and secondary organic carbon (SOC) decreased obviously. However, SIA and SOC are observed to play an important role in contributing to the rapid growth process of PM 2.5 under unfavorable meteorological conditions during the control period. In view of the gradual improvement of air quality in Beijing, as well as the contribution of secondary aerosol formations in total PM 2.5 , effective control of primary gaseous pollutants and volatile organic compounds (VOCs) will be very significant for further lowering the concentration of PM 2.5 in Beijing in normal time. [ABSTRACT FROM AUTHOR]