Formation and evolution mechanism of regional haze: a case study in the megacity Beijing, China

Abstract

The main objective of this study is to investigate the formation and evolution mechanism of the regional haze in megacity Beijing by analyzing the process of a severe haze that occurred 20–27 September 2011. Mass concentration and size distribution of aerosol particles as well as aerosol optical properties were concurrently measured at the Beijing urban atmospheric environment monitoring station. Gaseous pollutants (SO₂, NO-NO₂-NO_x, O₃, CO) and meteorological parameters (wind speed, wind direction, and relative humidity) were simultaneously monitored. Meanwhile, aerosol spatial distribution and the height of planetary boundary layer (PBL) were retrieved from the signal of satellite and LIDAR (light detection and ranging). Concentrations of NO, NO₂, SO₂, O₃, and CO observed during 23–27 September had exceeded the national ambient air quality standards for residents. The mass concentration of PM_2.5 gradually accumulated during the measurement and reached at 220 μg m⁻³ on 26 September, and the corresponding atmospheric visibility was only 1.1 km. The daily averaged AOD in Beijing increased from ~ 0.16 at λ = 500 nm on 22 September and reached ~ 3.5 on 26 September. The key factors that affected the formation and evolution of this haze episode were stable anti-cyclone synoptic conditions at the surface, decreasing of the height of PBL, heavy pollution emissions from urban area, number and size evolution of aerosols, and hygroscopic growth for aerosol scattering. This case study may provide valuable information for the public to recognize the formation mechanism of the regional haze event over the megacity, which is also useful for the government to adopt scientific approach to forecast and eliminate the occurrence of regional haze in China

Mixing ratio and carbon isotopic composition investigation of atmospheric CO 2 in Beijing, China

“…The air quality in this region dramatically changed because of the emissions of air pollutants coupled with CO 2 from house heating, traffic and industrial activities (Zhao et al, 2012;Chan and Yao, 2008). Studies on the air quality in Beijing have focused on the physicochemical properties and sources of atmospheric pollutants (Gao et al, 2014, Guo et al, 2012Zhang et al, 2013;Zhao et al, 2013), temporal and spatial distribution characteristics Schleicher et al, 2013;Zhao et al, 2009), and formation and evolution mechanisms Liu et al, 2013;Zhao et al, 2013). Some studies have paid attention to the isotopic composition of water vapor and precipitation in Beijing (Wen et al, 2012(Wen et al, , 2010(Wen et al, , 2008 and the hydrochemical and isotopic characteristics of atmospheric precipitation (Zhai et al, 2013).…”

Secondary Formation of Sulfate and Nitrate during a Haze Episode in Megacity Beijing, China

“…Thus, a non-haze episode was defined from 20-22 September. During the haze episode, the wind speed was relatively low with a mean value of 0.7 m s -1 , and there were no strong pressure gradients over Beijing (as discussed in Liu et al (2013)), which meant relatively weak air circulation over the region. This relatively stable synoptic condition limited the dispersion of air pollutants and led to an increase in the pollutant concentrations.…”

“…All of the observation instruments involved in this study except ACSM were described in detail in Liu et al (2013), and the time series of the meteorological parameters are illustrated in Fig. 2 Ng et al (2011) and Sun et al (2012).…”

“…Previous studies have found that haze is characterized by a high loading of fine particles and high fractions of secondary species of sulfates, nitrates and ammonium (SNA) in the fine particles Wang et al, 2012;Liu et al, 2013). Thus, understanding the formation mechanism of SNA will help understand the formation mechanism of haze.…”

“…In previous study, we generally discussed the formation and evolution mechanism of a regional haze episode in megacity Beijing from 20 September to 27 September, 2011 (Liu et al, 2013). Particle mass concentration and size distribution, aerosol optical properties, gas pollutants and meteorological parameters were measured.…”