Origin and transformation of ambient volatile organic compounds during a dust-to-haze episode in northwest China

• 發表在: Atmospheric Chemistry and Physics
• Main Authors: Y. Xue, Y. Huang, S. S. H. Ho, L. Chen, L. Wang, S. Lee, J. Cao
• 格式: Article
• 語言: 英语
• 出版: Copernicus Publications 2020-05-01
• 在線閱讀: https://www.atmos-chem-phys.net/20/5425/2020/acp-20-5425-2020.pdf
• ISSN: 1680-7316; 1680-7324

<p>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 <span class="inline-formula">TiO₂</span> and <span class="inline-formula">Fe</span> 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&thinsp;%) and biomass burning (18&thinsp;%) 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 (<span class="inline-formula">Fe</span>) and titanium (<span class="inline-formula">Ti</span>) was found in the airborne particles, together with a fast decrease in <i>trans</i>-/<i>cis</i>-2-butene ratios, which demonstrated that dust can accelerate the oxidation of ambient VOCs and the formation of secondary organic aerosol (SOA) precursors.</p>