Impact of anthropogenic emissions on biogenic secondary organic aerosol: observation in the Pearl River Delta, southern China

• Main Authors: Y.-Q. Zhang, D.-H. Chen, X. Ding, J. Li, T. Zhang, J.-Q. Wang, Q. Cheng, H. Jiang, W. Song, Y.-B. Ou, P.-L. Ye, G. Zhang, X.-M. Wang
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-11-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/14403/2019/acp-19-14403-2019.pdf
• ISSN: 1680-7316; 1680-7324

<p>Secondary organic aerosol (SOA) formation from biogenic precursors is affected by anthropogenic emissions, which are not well understood in polluted areas. In this study, we accomplished a year-round campaign at nine sites in polluted areas located in the Pearl River Delta (PRD) region during 2015. We measured typical biogenic SOA (BSOA) tracers from isoprene, monoterpenes, and <span class="inline-formula"><i>β</i></span>-caryophyllene, as well as major gaseous and particulate pollutants and investigated the impact of anthropogenic pollutants on BSOA formation. The concentrations of BSOA tracers were in the range of 45.4 to 109&thinsp;ng&thinsp;m<span class="inline-formula">⁻³</span> with the majority composed of products from monoterpenes (SOA<span class="inline-formula">_M</span>, <span class="inline-formula">47.2±9.29</span>&thinsp;ng&thinsp;m<span class="inline-formula">⁻³)</span>, isoprene (SOA<span class="inline-formula">_I</span>, <span class="inline-formula">23.1±10.8</span>&thinsp;ng&thinsp;m<span class="inline-formula">⁻³)</span>, and <span class="inline-formula"><i>β</i></span>-caryophyllene (SOA<span class="inline-formula">_C</span>, <span class="inline-formula">3.85±1.75</span>&thinsp;ng&thinsp;m<span class="inline-formula">⁻³)</span>. We found that atmospheric oxidants, <span class="inline-formula">O_<i>x</i></span> (<span class="inline-formula">O₃</span> plus <span class="inline-formula">NO₂</span>), and sulfate correlated well with later-generation SOA<span class="inline-formula">_M</span> tracers, but this was not the case for first-generation SOA<span class="inline-formula">_M</span> products. This suggested that high <span class="inline-formula">O_<i>x</i></span> and sulfate levels could promote the formation of later-generation SOA<span class="inline-formula">_M</span> products, which probably led to the relatively aged SOA<span class="inline-formula">_M</span> that we observed in the PRD. For the SOA<span class="inline-formula">_I</span> tracers, both 2-methylglyceric acid (NO/<span class="inline-formula">NO₂</span>-channel product) and the ratio of 2-methylglyceric acid to 2-methyltetrols (<span class="inline-formula">HO₂</span>-channel products) exhibit <span class="inline-formula">NO_<i>x</i></span> dependence, indicating the significant impact of <span class="inline-formula">NO_<i>x</i></span> on SOA<span class="inline-formula">_I</span> formation pathways. The SOA<span class="inline-formula">_C</span> tracer was elevated in winter at all sites and was positively correlated with levoglucosan, <span class="inline-formula">O_<i>x</i></span>, and sulfate. Thus, the unexpected increase in SOA<span class="inline-formula">_C</span> in wintertime might be highly associated with the enhancement of biomass burning, <span class="inline-formula">O₃</span> chemistry, and the sulfate component in the PRD. The BSOAs that were estimated using the SOA tracer approach showed the highest concentration in fall and the lowest concentration in spring with an annual average concentration of <span class="inline-formula">1.68±0.40</span>&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span>. SOA<span class="inline-formula">_M</span> dominated the BSOA mass all year round. We also found that BSOA correlated well with sulfate and <span class="inline-formula">O_<i>x</i></span>. This implied a significant effect from anthropogenic pollutants on BSOA formation and highlighted that we could reduce BSOA by controlling the anthropogenic emissions of sulfate and <span class="inline-formula">O_<i>x</i></span> precursors in polluted regions.</p>