Abstract
Severe haze events during which particulate matter (PM) increases quickly from tens to hundreds of microgram per cubic meter in 1–2 days frequently occur in China. Although it has been known that PM is influenced by complex interplays among emissions, meteorology, and physical and chemical processes, specific mechanisms remain elusive. Here, a new positive feedback mechanism between planetary boundary layer (PBL), relative humidity (RH), and secondary PM (SPM) formation is proposed based on a comprehensive field experiment and model simulation. The decreased PBL associated with increased PM increases RH by weakening the vertical transport of water vapor; the increased RH in turn enhances the SPM formation through heterogeneous aqueous reactions, which further enhances PM, weakens solar radiation, and decreases PBL height. This positive feedback, together with the PM-Radiation-PBL feedback, constitutes a key mechanism that links PM, radiation, PBL properties (e.g. PBL height and RH), and SPM formation, This mechanism is self-amplifying, leading to faster PM production, accumulation, and more severe haze pollution.
Highlights
China has been experiencing heavy air pollution in the past two decades, with frequent severe haze events[1,2]
The complex interplays among emissions, planetary boundary layer (PBL) meteorology, and atmospheric chemical processes make it more difficult to understand the formation of severe haze events[11,12,13,14,15]
During the 2014 Asia-Pacific Economic Cooperation (APEC) summit, a series of emission control measures[8,29] was implemented during 2–12 Nov. 2014 to ensure good air quality, providing a unique opportunity to understand the effect of emission reduction and the complex interplays between aerosols, meteorology, and atmospheric chemical processes
Summary
China has been experiencing heavy air pollution in the past two decades, with frequent severe haze events[1,2]. During the 2014 Asia-Pacific Economic Cooperation (APEC) summit, a series of emission control measures[8,29] was implemented during 2–12 Nov. 2014 to ensure good air quality, providing a unique opportunity to understand the effect of emission reduction and the complex interplays between aerosols, meteorology (wind, radiation, PBL, and RH), and atmospheric chemical processes. We capitalized on this opportunity by organizing a comprehensive field campaign in the urban area of Beijing. This paper analyzes the data and presents the major findings from this campaign
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