Integrated evaluation of aerosols from regional brown hazes over northern China in winter: Concentrations, sources, transformation, and mixing states

Abstract

[1] To evaluate the wintertime regional brown haze in northern China, trace gases and aerosols were measured at an urban site between 9 and 20 November 2009. Ion chromatography and transmission electron microscopy (TEM) were used to investigate soluble ions in PM 2.5 and the mixing state of individual particles. The contrasts between clear and hazy days were examined in detail. Concentrations of the primary gases including NO (55.62 ppbv), NO 2 (54.86 ppbv), SO 2 (83.03 ppbv), and CO (2.07 ppmv) on hazy days were 2 to 6 times higher than those on clear days. In contrast, concentrations of O 3 remained low (5.71 ppbv) on hazy days. Mass concentrations of PM 2.5 (135.90 mg m −3 ) and BC (7.85 mg m −3 ) were 3 times higher on hazy days than on clear days. Based on the estimations from TEM analysis, fractions of both ammoniated sulfate (AS)-soot (20%) and AS-soot/organic matter/fly ash (20%) were larger on hazy days than on clear days (13% and 12%), implying that coagulation is an important mixing process in the polluted air. The SO 2 emissions from coal combustion for power plants, industrial activities, and household heating led to high concentrations. Also, high concentrations of secondary sulfates significantly formed in the haze. Therefore, high concentrations of acidic gases contributed to the increased mass and number of secondary aerosols. Our study indicates that metal-catalyzed oxidation in the aqueous phase is a major pathway of sulfate formation. The mixtures of aerosol particles, together with MODIS images, suggest that the hazes covered not only the industrial cities, but extended into the neighboring rural regions.

Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

“…The deteriorated haze pollution was related to the increase in anthropogenic emissions (Qu et al 2015) and the variations in atmospheric circulations (Hui and Xiang, 2015;Li et al, 2016). These haze layers could spread across northern and eastern China and persist over a week during autumn and winter, inducing elevated PM 2.5 concentration exceeding 500 μg m −3 and instantaneous visibility degradation to less than 200 m Li, Zhou et al, 2011). The tremendous aerosol loading arising from frequent haze events exerted a profound impact on the radiation balance and weather in eastern China (Liang and Xia, 2005;Liu et al, 2007;Gao et al, 2015).…”

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

“…7, the SOR ratio presented an upward trend from a non-haze episode to a haze episode: the average value of SOR was 0.05 in non-haze episodes with a highest value of 0.11, whereas the average value of SOR was 0.27 in haze episodes with a highest value of 0.62, which indicated more intense secondary formation of sulfate in haze episodes. Previous studies suggested that the conversion of SO 2 to sulfate during a haze episode in winter was mainly through the aqueous-phase oxidation of SO 2 by the catalytic oxidation of iron and manganese with weak photochemical activity (low O 3 concentration, high NO 2 concentration and low temperature) during the haze period Li et al, 2011;Wang et al, 2012;Zhao et al, 2013). To evaluate the effect of gas-phase oxidation of SO 2 during the haze period, we analyzed the correlations of SOR with O 3 and temperature in haze episodes and found that low correlations existed between SOR and O 3 (r = -0.53, p = 0.01) and SOR and temperature (r = -0.53, p = 0.01).…”

“…Sulfate formation in aqueous solution is generated by the uptake of SO 2 onto wet, pre-existing particles or cloud droplets followed by oxidation by O 3 , H 2 O 2, NO 2 or O 2 catalyzed by Fe(III) and Mn(II) (Seinfeld and Pandis, 2006;Wang et al, 2012). Previous studies found that sulfate is produced mainly by heterogeneous reactions by oxidizing SO 2 on wet, pre-existing particles or cloud droplets under high relative humidity (RH) conditions in haze episode in winter Li et al, 2011;Wang et al, 2012;Zhao et al, 2013). Both laboratory experiments and in situ observations suggest that the aqueous oxidation of SO 2 is attributed to catalysis by metals, such as iron and manganese (Turšič et al, 2003;Li et al, 2011;Wang et al, 2012).…”

“…Previous studies found that sulfate is produced mainly by heterogeneous reactions by oxidizing SO 2 on wet, pre-existing particles or cloud droplets under high relative humidity (RH) conditions in haze episode in winter Li et al, 2011;Wang et al, 2012;Zhao et al, 2013). Both laboratory experiments and in situ observations suggest that the aqueous oxidation of SO 2 is attributed to catalysis by metals, such as iron and manganese (Turšič et al, 2003;Li et al, 2011;Wang et al, 2012). The formation pathway of nitrates, however, is less well known compared to the formation of sulfate, and it is influenced by the emission load of the precursors, the concentrations of oxidants in both the gas and the liquid phase, the characteristics of pre-existing particles and meteorological conditions (Seinfeld and Pandis, 2006;Pathak et al, 2009;Guo et al, 2010;Ye et al, 2011;He et al, 2012).…”

Numerical Investigation of the Diffusion Feature of Aerosol

“…haze-fog) have drawn more and more attention [1,2] . Aerosol is a suspension system that composed of small solid ________________________ particles in the air, which is an important source of material to form fog-haze days [3,4] .…”