Aerosol physicochemical properties and implications for visibility during an intense haze episode during winter in Beijing

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.

Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements

“…Synergetic effects among various organic and inorganic compounds may exist under highly polluted conditions, indicating different PM formation rates between developing and developed urban regions. Indeed, a large enhancement of particulate sulfate was typically observed during regional haze events in China Wang et al, 2015;Fu et al, 2008;Xie et al, 2015). Currently, the highly elevated sulfate concentration during haze events cannot be fully explained by model simulations (Wang et al, 2014a;Chen et al, 2016).…”

The interdecadal worsening of weather conditions affecting aerosol pollution in the Beijing area in relation to climate warming

“…In the BIV, aerosol pollution has become 18 increasingly serious during the past decades, particularly since 2010 (Zhang et al, 2015); in 19 January 2013, February 2014, December 2015, December 2016to 10 January, 2017 persistent HPEs occurred in Beijing, and the mass concentrations of PM2.5 were high at 21 historically high levels (Zhong et al, 2018). There will be a detailed discussion on this issue 22 in a later section.…”

“…Aerosol pollution in the BIV 33 region has reached a very serious level since 2010 (Zhang et al, 2015), which was much 34 higher than that in the 1980s. Remarkably, more aerosols back-scattered a larger amount of 35 radiation into space, which caused a significant reduction in radiation reaching the ground.…”

“…Specifically, aerosol pollution in Beijing has been 17 possibly affected by southerly/southwesterly surface winds . Aerosol pollution was also found 18 to become increasingly serious during recent decades (Zhang et al, 2015), which is partially 19 due to increasing emissions in air pollutants from anthropogenic activities (e.g., traffic, 20 industry, and power plants) (Li et al, 2017), but it is also influenced by regional and 21 unfavorable weather conditions (Zhang et al, 2015 another (Sui et al, 2007;Pang et al, 2009 humidity, evaporability, stability, and the effective parameter associated with the contribution 17 of air pollution β(c'), respectively. Furthermore, the final PLAM can be attributed to two 18 major separate factors: (1) initial meteorological conditions α(m) associated with atmospheric 19 condensation processes and (2) a dynamic effective parameter associated with the initial 20 contribution of air pollution β(c'), which can be expressed as follows 21 , 1960-1989), the temperature anomaly (δT) from 1960 to 2017 at different pressure layers 20 (1000 -100 hPa) was calculated.…”

“…Since individuals experienced heavy aerosol pollution episodes (HPES) in January 2013 5 in Beijing and its vicinity (BIV) in central-eastern China, changes in aerosol particle 6 concentrations and their chemical components have attracted special attention to high 7 population density areas with rapid economic growth (Huang et al, 2014;Zhang et al, 8 2013;Guo et al, 2014;Wang et al, 2014a;Wang et al, 2014b;Wang et al, 2015;Sun et al, 9 2014). However, these studies were mainly concerned with changes in emission sources and 10 changes in atmospheric physio-chemical characterizations.…”