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https://doi.org/10.5194/acp-2019-1080
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1080
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 29 Jan 2020

Submitted as: research article | 29 Jan 2020

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This preprint is currently under review for the journal ACP.

Characterization of submicron particles by Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) during wintertime: aerosol composition, sources and chemical processes in Guangzhou, China

Junchen Guo1, Shengzhen Zhou1,8, Minfu Cai1, Jun Zhao1,8, Wei Song2, Weixiong Zhao3, Weiwei Hu2, Yele Sun4, Yao He4, Chengqiang Yang3, Xuezhe Xu3, Zhisheng Zhang5, Peng Cheng6, Qi Fan1, Jian Hang1, Shaojia Fan1, Xinming Wang2, and Xuemei Wang7 Junchen Guo et al.
  • 1School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, and Institute of Earth Climate and Environment System, Sun Yat-sen University, Guangzhou, 510275, P. R. China
  • 2State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, P. R. China
  • 3Laboratory of Atmospheric Physico-Chemistry, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, P. R. China
  • 4State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, P. R. China
  • 5South China Institute of Environmental Sciences, Ministry of Ecologyand Environment, Guangzhou, 510655, China
  • 6Institute of Technology on Atmospheric Environmental Safety and Pollution Control, Jinan University, Guangzhou, 510632, P. R. China
  • 7Institute for Environmental and Climate Research, Jinan University, Guangzhou,511443, P. R. China
  • 8Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519082, P. R. China

Abstract. Particulate matter (PM) pollution in China is an emerging environmental issue which policy makers and public have increasingly paid attention to. In order to investigate the characteristics, sources, and chemical processes of PM pollution in Guangzhou, a field measurement was conducted from 20 November 2017 to 5 January 2018, with a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) and other collocated instruments. Mass concentrations of non-refractory submicron particulate matters (NR-PM1) measured by the ToF-ACSM were correlated well with those of PM2.5 or PM1.1 measured by filter-based methods. The organic mass fraction increased from 45 % to 53 % when the air switched from non-pollution periods to pollution episodes, indicating significant roles of organic aerosols (OA) during the whole study. Based on the mass spectra measured by the TOF-ACSM, Positive Matrix Factorization (PMF) with multilinear engine (ME-2) algorithm was performed to deconvolve OA into four factors, including hydrocarbon-like OA (HOA, 12 %), cooking OA (COA, 18 %), semi-volatile oxygenated OA (SVOOA, 30 %), and low-volatility oxygenated OA (LVOOA, 40 %). Furthermore, we found that SVOOA and nitrate were significantly contributed from local traffic emissions while sulfate and LVOOA were mostly attributed to regional pollutants. Comparisons between this work and other previous studies in China show that SOA fraction in total OA increases spatially across China from the North to the South.

Two distinctly opposite trends for NR-PM1 formation were observed during non-pollution period and pollution EPs. The ratio of secondary PM (SPM = SVOOA + LVOOA + sulfate + nitrate + ammonium) to primary PM (PPM = HOA + COA + chloride), together with peroxy radicals RO2* and ozone, increased with increasing NR-PM1 concentration during non-pollution period, while an opposite trend of these three quantities was observed during pollution EPs. Furthermore, oxidation degrees of both OA and SOA were investigated using the f44/f43 space and the results show that at least two OOA factors are needed to cover a large range of f44 and f43 in Guangzhou. Comparisons between our results and other laboratory studies imply that volatile organic compounds (VOCs) from traffic emissions in particular from diesel combustion and aromatic compounds are most possible SOA precursors in Guangzhou. Peroxy radical RO2* was used as a tracer for SOA formed through gas phase oxidation. For non-pollution period, SOA concentration was reasonably correlated with RO2* concentration during both daytime and nighttime, suggesting that gas phase oxidation was primarily responsible for SOA formation. For pollution EPs, when NR-PM1 mass concentration was divided into six segments, in each segment except for the lowest one, SOA concentration was correlated moderately with RO2* concentration, suggesting that gas phase oxidation still plays important roles in SOA formation. In addition, the slopes of linear regressions for the above correlations increased with increasing NR-PM1 mass concentration, probably representing enhanced gas-to-particle partitioning under high NR-PM1 concentration. The intercepts of the above linear regressions, which correspond to the extent of other mechanisms (i.e., heterogeneous and multiphase reactions), increased with increasing NR-PM1 mass concentration. Our results suggest that while gas phase oxidation contributes predominantly to SOA formation during non-pollution periods, other mechanisms such as heterogeneous and multiphase reactions play more important roles in SOA formation during pollution EPs than gas phase oxidation.

Junchen Guo et al.

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Short summary
We characterized non-refractory submicron particulate matters (PM1.0) during winter time in Guangzhou, South China. Chemical composition and key sources of ambient PM1.0 are revealed, highlighting the significant roles of SOA. The relationship with SOA and peroxy radicals indicated gas phase oxidation contributed predominantly to SOA formation during non-pollution periods, while heterogeneous/multiphase reactions played more important roles in SOA formation during pollution periods.
We characterized non-refractory submicron particulate matters (PM1.0) during winter time in...
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