"APEC Blue": Secondary Aerosol Reductions from Emission Controls in Beijing.

Yele Sun,Douglas R Worsnop,Wei Du,Qi Zhang,Qingqing Wang,Jie Li,Chen Chen,Tingting Han,Jianguo Liu,Xiaole Pan,Pingqing Fu,Zifa Wang,Libo Zhou,Weiqi Xu,Xiaofeng Guo,Oliver Wild,Haitao Zheng

doi:10.1038/srep20668

Abstract

China implemented strict emission control measures in Beijing and surrounding regions to ensure good air quality during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. We conducted synchronous aerosol particle measurements with two aerosol mass spectrometers at different heights on a meteorological tower in urban Beijing to investigate the variations in particulate composition, sources and size distributions in response to emission controls. Our results show consistently large reductions in secondary inorganic aerosol (SIA) of 61–67% and 51–57%, and in secondary organic aerosol (SOA) of 55% and 37%, at 260 m and ground level, respectively, during the APEC summit. These changes were mainly caused by large reductions in accumulation mode particles and by suppression of the growth of SIA and SOA by a factor of 2–3, which led to blue sky days during APEC commonly referred to as “APEC Blue”. We propose a conceptual framework for the evolution of primary and secondary species and highlight the importance of regional atmospheric transport in the formation of severe pollution episodes in Beijing. Our results indicate that reducing the precursors of secondary aerosol over regional scales is crucial and effective in suppressing the formation of secondary particulates and mitigating PM pollution.

Highlights

Fine particles (particulate matter with aerodynamic diameter less than 2.5 micrometers) exert large impacts on visibility reduction[1], radiative forcing[2], and public health[3,4]
Fine particles exert large impacts on visibility reduction[1], radiative forcing[2], and public health[3,4]
Asia-Pacific Economic Cooperation (APEC) was dominated by secondary nitrate, which accounted for 27–29% of the PM1 mass at the ground site and 28–31% at 260 m (Fig. 1)

Summary

Introduction

Fine particles (particulate matter with aerodynamic diameter less than 2.5 micrometers) exert large impacts on visibility reduction[1], radiative forcing[2], and public health[3,4]. The SIA and SOA together contributed 79–83% and 63–72% to the total submicron mass at the ground site and 260 m, highlighting the importance of secondary aerosol formation during haze episodes[9,10].

Results

Conclusion