Abstract
Abstract. The evolution of physical, chemical and optical properties of urban aerosol particles was characterized during an extreme haze episode in Beijing, PRC, from 24 through 31 January 2013 based on in situ measurements. The average mass concentrations of PM1, PM2.5 and PM10 were 99 ± 67 μg m−3 (average ± SD), 188 ± 128 μg m−3 and 265 ± 157 μg m−3, respectively. A significant increase in PM1-2.5 fraction was observed during the most heavily polluted period. The average scattering coefficient at 550 nm was 877 ± 624 Mm−1. An increasing relative amount of coarse particles can be deduced from the variations of backscattering ratios, asymmetry parameter and scattering Ångström exponent. Particle number-size distributions between 14 and 2500 nm diameter showed high number concentrations, particularly in the nucleation mode and accumulation mode. Size-resolved chemical composition of submicron aerosol from a high-resolution time-of-flight aerosol mass spectrometer showed that the mass concentrations of organic, sulfate, nitrate, ammonium and chlorine mainly resided on particles between 500 and 800 nm (vacuum diameter), and nitrate and ammonium contributed greatly to particle growth during the heavily polluted day (28 January). Increasing relative humidity and stable synoptic conditions on 28 January combined with heavy pollution on 28 January, leading to enhanced water uptake by the hygroscopic submicron particles and formation of secondary aerosol, which might be the main reasons for the severity of the haze episode. Light-scattering apportionment showed that organic, sulfate, ammonium nitrate and ammonium chloride compounds contributed to light-scattering fractions of 54, 24, 12 and 10%, respectively. This study indicated that the organic component in submicron aerosol played an important role in visibility degradation during the haze episode in Beijing.
Highlights
Atmospheric aerosol particles play a significant role in radiation balance and climate forcing through direct scattering and absorption of solar radiation (Anderson et al, 2003; Pöschl, 2005; Ramanathan et al, 2001)
Based on in situ measurements, the physical and chemical properties of aerosol particles were characterized during a severe haze episode in Beijing from 24 to 31 January 2013
The average mass concentrations of PM1, PM2.5 and PM10 were 99.1 ± 67.1, 188.3 ± 128.8 and 265.2 ± 157.1 μg m−3, respectively, and an increasing fraction of PM1−2.5 was significant during the heaviest pollution periods
Summary
Atmospheric aerosol particles play a significant role in radiation balance and climate forcing through direct scattering and absorption of solar radiation (Anderson et al, 2003; Pöschl, 2005; Ramanathan et al, 2001). They can act as cloud condensation nuclei (CCN) and thereby change the cloud albedo and lifetime (Twomey, 1977). Along with the rapid economic growth in China, its capital city, Beijing, has suffered substantially from air quality deterioration and visibility degradation, though the mass concentration of PM10 has decreased in Beijing in the last 10 years (Liu et al, 2015). The mass loading of fine aerosol particles and their precursors
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