Articles | Volume 17, issue 1
Research article
02 Jan 2017
Research article |  | 02 Jan 2017

Air quality improvement in a megacity: implications from 2015 Beijing Parade Blue pollution control actions

Wen Xu, Wei Song, Yangyang Zhang, Xuejun Liu, Lin Zhang, Yuanhong Zhao, Duanyang Liu, Aohan Tang, Daowei Yang, Dandan Wang, Zhang Wen, Yuepeng Pan, David Fowler, Jeffrey L. Collett Jr., Jan Willem Erisman, Keith Goulding, Yi Li, and Fusuo Zhang

Abstract. The implementation of strict emission control measures in Beijing and surrounding regions during the 2015 China Victory Day Parade provided a valuable opportunity to investigate related air quality improvements in a megacity. We measured NH3, NO2 and PM2.5 at multiple sites in and outside Beijing and summarized concentrations of PM2.5, PM10, NO2, SO2 and CO in 291 cities across China from a national urban air quality monitoring network between August and September 2015. Consistently significant reductions of 12–35 % for NH3 and 33–59 % for NO2 in different areas of Beijing during the emission control period (referred to as the Parade Blue period) were observed compared with measurements in the pre- and post-Parade Blue periods without emission controls. Average NH3 and NO2 concentrations at sites near traffic were strongly correlated and showed positive and significant responses to traffic reduction measures, suggesting that traffic is an important source of both NH3 and NOx in urban Beijing. Daily concentrations of PM2.5 and secondary inorganic aerosol (sulfate, ammonium and nitrate) at the urban and rural sites both decreased during the Parade Blue period. During (after) the emission control period, concentrations of PM2.5, PM10, NO2, SO2 and CO from the national city-monitoring network showed the largest decrease (increase) of 34–72 % (50–214 %) in Beijing, a smaller decrease (a moderate increase) of 1–32 % (16–44 %) in emission control regions outside Beijing and an increase (decrease) of 6–16 % (−2–7 %) in non-emission-control regions of China. Integrated analysis of modelling and monitoring results demonstrated that emission control measures made a major contribution to air quality improvement in Beijing compared with a minor contribution from favourable meteorological conditions during the Parade Blue period. These results show that controls of secondary aerosol precursors (NH3, SO2 and NOx) locally and regionally are key to curbing air pollution in Beijing and probably in other mega cities worldwide.

Short summary
This paper evaluates the effectiveness of emission control measures implemented in Beijing during the Parade Blue period by integrating our own results, official-released data and modeling data. We demonstrate that emission control measures make a major contribution to air quality improvement in Beijing and surrounding regions. We conclude a joint local and regional control of secondary aerosol precursors to be key to curbing air pollution in Beijing.
Final-revised paper