Tracer-based source apportioning of atmospheric organic carbon and the influence of anthropogenic emissions on secondary organic aerosol formation in Hong Kong

• Main Authors: Y. Cheng, Y. Ma, D. Hu
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-07-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/10589/2021/acp-21-10589-2021.pdf

<p>Here we conducted comprehensive chemical characterization and source apportionment of 49 PM<span class="inline-formula">_2.5</span> samples collected in Hong Kong. Besides the major aerosol constituents, 39 polar organic species, including 14 secondary organic aerosol (SOA) tracers of isoprene, monoterpenes, <span class="inline-formula"><i>β</i></span>-caryophyllene, and naphthalene, were quantified using gas chromatography–mass spectrometry (GC–MS). Six factors, i.e., SOA, secondary sulfate (SS), biomass burning (BB)/SOA, sea salt, marine vessels, and vehicle emissions, were apportioned by positive matrix factorization (PMF) as the major sources of ambient organic carbon (OC) in Hong Kong. The secondary formation, including OC from SOA, SS, and aging of BB plume, was the leading contributor to OC (51.4 %, 2.15 <span class="inline-formula">±</span> 1.37 <span class="inline-formula">µg C m⁻³</span>) throughout the year. We then applied a tracer-based method (TBM) to estimate the SOA formation from the photo-oxidation of four selected precursors, and monoterpene SOA was the most abundant. A Kintecus kinetic model was used to examine the formation channels of isoprene SOA, and the aerosol-phase ring-opening reaction of isoprene epoxydiols (IEPOXs) was found to be the dominant formation pathway. Consistently, IEPOX tracers contributed 94 % to total GC–MS-quantified isoprene SOA tracers. The TBM-estimated secondary organic carbon (SOC<span class="inline-formula">_TBM</span>) and PMF-apportioned SOC (SOC<span class="inline-formula">_PMF</span>) showed similar temporal trends; however, SOC<span class="inline-formula">_TBM</span> only accounted for 26.5 % of SOC<span class="inline-formula">_PMF</span>, indicating a large fraction of ambient SOA was from other reaction pathways or precursors. Results of Pearson's <span class="inline-formula"><i>R</i></span> and multivariate linear regression analysis showed that NO<span class="inline-formula">_<i>x</i></span> processing played a key role in both daytime and nighttime SOA production in the region. Moreover, sulfate had a significant positive linear relationship with SOC<span class="inline-formula">_PMF</span> and SS-related SOC, and particle acidity was significantly correlated with SOC from the aging of BB.</p>