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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1008
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Comparison of secondary organic aerosol formation from toluene on initially wet and dry ammonium sulfate particles
Tengyu Liu1, Dan Dan Huang1, Zijun Li2, Qianyun Liu3, ManNin Chan2,4, and Chak K. Chan1 1School of Energy and Environment, City University of Hong Kong, Hong Kong, China
2Earth System Science Programme, The Chinese University of Hong Kong, Hong Kong, China
3Division of Environment and Sustainability, Hong Kong University of Science and Technology, Hong Kong, China
4The Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Hong Kong, China
Abstract. The formation of secondary organic aerosol (SOA) has been widely studied in the presence of dry seed particles at low relative humidity (RH). At higher RH, seed particles can exist as dry or wet particles. Here, we investigated the formation of SOA from the photooxidation of toluene using an oxidation flow reactor under a range of OH exposures on initially wet or dry ammonium sulfate (AS) seed particles at an RH of 68 %. At an OH exposure of 4.66 × 1010 molecules cm -3 s, the ratio of the SOA yield on wet AS seeds to that on dry AS seeds was 1.31 ± 0.02. However, this ratio decreased to 1.01 ± 0.01 at an OH exposure of 5.28 × 1011 molecules cm -3 s. The decrease in the ratios of SOA yields as the increase of OH exposure may be due to the early deliquescence of initially dry AS seeds after coated by highly oxidized toluene-derived SOA. SOA formation lowered the deliquescence RH of AS and resulted in the uptake of water by both AS and SOA. Hence the initially dry AS seeds contained aerosol liquid water (ALW) soon after a large fraction of SOA formed and the SOA yield and ALW approached those of the initially wet AS seeds as OH exposure and ALW increased. However, a higher oxidation state of the SOA on initially wet AS seeds than that on dry AS seeds was observed at all levels of OH exposure. The difference in mass fractions of m/z 29, 43 and 44 of SOA mass spectra indicated that SOA formed on initially wet seeds may be enriched in earlier-generation products containing carbonyl functional groups at low OH exposures and later-generation products containing acidic functional groups at high exposures. Our results suggest that AS dry seeds soon turn to at least partially deliquesced particles during SOA formation and more studies on the interplay of SOA formation and ALW are warranted.

Citation: Liu, T., Huang, D. D., Li, Z., Liu, Q., Chan, M., and Chan, C. K.: Comparison of secondary organic aerosol formation from toluene on initially wet and dry ammonium sulfate particles, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1008, in review, 2017.
Tengyu Liu et al.
Tengyu Liu et al.

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Short summary
The formation of SOA from toluene on initially dry and wet AS seeds was compared using an OFR at an RH of 68 %. We found that as OH exposure increased, the SOA yield and ALW of the initially dry seeds approached those of the initially wet seeds while the wet seeds yielded SOA of a higher degree of oxidation at all exposure levels. Our results suggest that AS dry seeds soon at least partially deliquesced during SOA formation and more studies on the interplay of SOA formation and ALW are warranted.
The formation of SOA from toluene on initially dry and wet AS seeds was compared using an OFR at...
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