Analysis of a winter regional haze event and its formation mechanism in the North China Plain

Abstract

A regional haze episode occurred in the Beijing, Tianjin and Hebei province (BTH) area in the North China Plain (NCP) from 16 to 19 January 2010. The chemical and optical properties of aerosols and the meteorological condition were investigated in this study with intensive measurement of aerosol and trace gases from 14 to 23 January 2010 at five sites. The episode was caused by the combination of anthropogenic emissions and surface air stagnation under a high pressure system followed by a low pressure system. The concentrations of PM<sub>2.5</sub> and trace gases increased significantly on a regional scale during this episode. The increased aerosol scattering coefficient (σ<sup>sp</sup>), absorption coefficient (σ<sub>ap</sub>), and aerosol optical depth (AOD) showed the importance of aerosol extinction during this haze episode. The increase of secondary inorganic pollutants (SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>) was observed simultaneously at four sites, especially in the plain area of BTH, which could be identified as a common characteristic of pollution haze in east China. The organic matter (OM) was different from secondary inorganic pollutants, which increased more significantly at Chengde (CD) site than the other three sites in plain area. The sulfate and nitrate in PM<sub>2.5</sub> were mainly formed through the heterogeneous reaction process in the urban area. The secondary organic aerosols in PM<sub>2.5</sub> only existed during haze days at CD but in both haze and normal days at the other three sites. The chemical characteristics of aerosols in PM<sub>2.5</sub> indicated that the secondary formation of aerosol was one important mechanism in the formation of haze episode. The strong temperature inversion and descending air motions in the planetary boundary layer (PBL) allowed pollutants to accumulate in a shallow layer. The weak surface wind speed produced high pollutants concentration within these source regions. The accumulation of pollutants was one main factor in the haze formation. The enhanced southwest wind in the last period of this episode transported pollutants to the downwind area and expanded the regional scope of the haze

Characteristics and source apportionment of PM2.5 during a fall heavy haze episode in the Yangtze River Delta of China

“…Moreover, in consideration of the fact that sulfate, nitrate, ammonium and organic aerosol are the dominant components of PM 2.5 in Shanghai, gas-to-particle conversion is also likely a significant contributor to haze formation in YRD (Yao et al, 2002;Wang et al, 2006;Ye et al, 2003;Yang et al, 2005;Feng et al, 2009). Particle hygroscopic growth from high humidity and biomass burning after harvests often leads to heavy pollution in winter (Zhang et al, 2012;Zhao et al, 2013). However, most studies focus on winter, while haze in fall is also severe and complicated.…”

Characteristics of volatile organic compounds and their role in ground-level ozone formation in the Beijing-Tianjin-Hebei region, China

“…The region suffers from serious photochemical pollution and haze (Tang et al, 2009;Han et al, 2013). The hourly average concentrations of PM 2.5 in Beijing reach 318 mg/m 3 on hazy days (Zhao et al, 2013), and cities in Hebei province suffer from even greater atmospheric pollution . Ding et al (2009) reported worsening photochemical pollution in Beijing and the North China Plain.…”

The variation of chemical characteristics of PM2.5 and PM10 and formation causes during two haze pollution events in urban Beijing, China

“…Multiple studies on the characteristics of atmospheric aerosols during haze episodes in Beijing have been carried out during the past few years. Crustal matters, secondary aerosol, and organic materials are identified as the three main chemical components of the aerosols in Beijing Zhao et al, 2013). SO 4 2À , NO 3 À , and NH 4 þ represent the dominant water soluble inorganic ions (WSIIs) during haze episodes in aerosol (Z.Q.…”