Preprints
https://doi.org/10.5194/acp-2021-32
https://doi.org/10.5194/acp-2021-32

  20 Jan 2021

20 Jan 2021

Review status: this preprint is currently under review for the journal ACP.

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

Yubo Cheng1, Yiqiu Ma1,2, and Di Hu1,2 Yubo Cheng et al.
  • 1State Key Laboratory of Environmental and Biological Analysis, Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong, P. R. China
  • 2HKBU Institute of Research and Continuing Education, Shenzhen Virtual University Park, Shenzhen, 518057, P. R. China

Abstract. Here we conducted comprehensive chemical characterization and source apportionment of 49 PM2.5 samples collected in Hong Kong. Besides the major aerosol constituents, 39 polar organic species, including 14 secondary organic aerosol (SOA) tracers of isoprene, monoterpenes, β-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 ± 1.37 μgC m−3) 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 monoterpenes 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 (IEPOX) was found to be the dominant formation pathway. Consistently, IEPOX tracers contributed 94 % of total GC-MS quantified isoprene SOA tracers. The TBM-estimated SOC (SOCTBM) and PMF-resolved SOC (SOCPMF) showed similar temporal trends; however, SOCTBM only accounted for 26.5 % of SOCPMF, indicating a large fraction of ambient SOA was from other reaction pathways/precursors. Results of Pearson's R and multivariate linear regression analysis showed that NOx processing played a key role in both daytime and nighttime SOA production in the region. SOA formation through nighttime NO3 oxidation of biogenic VOCs, especially monoterpenes, may have made a considerable contribution to the SOA loading in Hong Kong. Moreover, sulfate had a significant positive linear relationship with SOCPMF and SS-related SOC, and particle acidity was significantly correlated with SOC from the aging of BB.

Yubo Cheng et al.

Status: open (until 17 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-32', Anonymous Referee #1, 29 Jan 2021 reply
  • RC2: 'Comment on acp-2021-32', Anonymous Referee #2, 11 Feb 2021 reply

Yubo Cheng et al.

Yubo Cheng et al.

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Short summary
We conducted comprehensive chemical characterization and source apportionment of PM2.5 samples collected in Hong Kong. Secondary formation was the leading contributor to OC throughout the year, and monoterpenes were the most significant SOA precursors in the region. Isoprene SOA was mainly formed from the aerosol phase reaction of isoprene epoxydiols. NOx processing played a key role in both daytime and nighttime SOA production, especially the nighttime NO3 oxidation of biogenic VOCs.
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