Abstract
Abstract. The high contribution of secondary organic aerosol to the loading of fine particle pollution in China highlights the roles of volatile organic compound (VOC) oxidation. In this respect, particulate active metallic oxides in dust, like TiO2 and Fe ions, were proposed to influence the photochemical reactions of ambient VOCs. A case study was conducted at an urban site in Xi'an, northwest China, to investigate the origin and transformation of VOCs during a windblown dust-to-haze pollution episode, and the assumption that dust would enhance the oxidation of VOCs was verified. Local vehicle exhaust (25 %) and biomass burning (18 %) were found to be the two largest contributors to ambient VOCs. In the dust pollution period, a sharp decrease in the loading of VOCs and the aging of their components were observed. Simultaneously, the secondary oxygenated VOC fraction (i.e., methylglyoxal) increased. Source strength, physical dispersion, and regional transport were eliminated as major factors for the variation of ambient VOCs. In another aspect, about a 2- to 3-fold increase in the loading of iron (Fe) and titanium (Ti) was found in the airborne particles, together with a fast decrease in trans-/cis-2-butene ratios, which demonstrated that dust can accelerate the oxidation of ambient VOCs and the formation of secondary organic aerosol (SOA) precursors.
Highlights
Secondary aerosols are important components of fine particles in China, which could contribute to about 30 % to 77 % of PM2.5 loading; in this respect, secondary organic aerosols (SOAs) take about half of the loading (Huang et al, 2014). Guo et al (2014) believed that gaseous emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) were responsible for the large secondary PM formation
We propose the possibility that windblown dust, which includes sustainable TiO2, can influence the atmospheric photochemistry of VOCs, which would accelerate the oxidation of ambient VOCs (Chu et al, 2019; Nie et al, 2014)
Combined with the findings regarding the composition of VOCs and PM2.5, these results indicate that the reactions of VOCs led to the formation of SOAs, and in so doing they contributed to the fine particle pollution
Summary
Secondary aerosols are important components of fine particles in China, which could contribute to about 30 % to 77 % of PM2.5 loading; in this respect, secondary organic aerosols (SOAs) take about half of the loading (Huang et al, 2014). Guo et al (2014) believed that gaseous emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) were responsible for the large secondary PM formation. Guo et al (2014) believed that gaseous emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) were responsible for the large secondary PM formation. Solid–gas heterogeneous reactions would cause the transformation of gaseous pollutants and change the property of particles (Zhang et al, 2000, 2003; He et al, 2014). The oxidation of organic and inorganic gas on particle surfaces through the transition-metal-catalyzed chain reaction was frequently found to play an important role on the trans-. Y. Xue et al.: Transformation of VOCs during windblown dust-to-haze pollution episode formation of ambient gas pollutants (Chu et al, 2019). The surface of mineral dust provides plenty of reactive sites for multiple atmospheric trace gas reactions (Cwiertny et al, 2008). Dust is considered to serve as a catalyst for reactive gases and to modify the photochemical processes (Dentener et al, 1996; Dickerson et al, 1997)
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