31 Aug 2020

31 Aug 2020

Review status: a revised version of this preprint is currently under review for the journal ACP.

Quantification of solid fuel combustion and aqueous chemistry contributions to secondary organic aerosol during wintertime haze events in Beijing

Yandong Tong1, Veronika Pospisilova1,a, Lu Qi1, Jing Duan2, Yifang Gu2, Varun Kumar1, Pragati Rai1, Giulia Stefenelli1, Liwei Wang1, Ying Wang2, Haobin Zhong2, Urs Baltensperger1, Junji Cao2, Ru-jin Huang2, Andre Stephan Henry Prevot1, and Jay Gates Slowik1 Yandong Tong et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland
  • 2Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
  • anow at: Tofwerk AG, Uttigenstrasse 22, 3600 Thun, Switzerland

Abstract. In recent years, intense haze events in megacities such as Beijing have received significant study. Although secondary organic aerosol (SOA) has been identified as a major contributor to such events, knowledge of its sources and formation mechanisms remains uncertain. We investigate this question through the first field deployment of the extractive electrospray ionisation time-of-flight mass spectrometer (EESI-TOF-MS) in Beijing, together with an Aerodyne long time-of-flight aerosol mass spectrometer (L-TOF AMS). Measurements were performed during autumn and winter 2017, capturing the transition from non-heating to heating seasons. Source apportionment resolved four factors related to primary organic aerosols (traffic, cooking, biomass burning, and coal combustion), as well as four related to secondary organic aerosol (SOA). Of the SOA factors, two were related to solid fuel combustion (SFC), one to SOA generated from aqueous chemistry, and one to mixed/indeterminate sources. The SFC factors were identified from spectral signatures corresponding to aromatic oxidation products, while the aqueous SOA factor was characterised by signatures of small organic acids and diacids, and unusually low CO+/CO2+ fragment ratios measured by the AMS. Solid fuel combustion was the dominant source of SOA during the heating season. However, a comparably intense haze event was also observed in the non-heating season, and was dominated by the aqueous SOA factor. Aqueous chemistry was promoted by the combination of high relative humidity and air masses passing over high NOx regions to the south and east of Beijing, leading to high particulate nitrate. The resulting high liquid water content was highly correlated with the concentration of the aqueous SOA factor. These results highlight the strong compositional variability between different haze events, indicating the need to consider multiple formation pathways and precursor sources to describe SOA during intense haze events in Beijing.

Yandong Tong et al.

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Status: final response (author comments only)
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Yandong Tong et al.

Yandong Tong et al.


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Short summary
We investigate SOA sources and formation processes by a field deployment of the EESI-TOF-MS and L-TOF AMS in Beijing in late fall and early winter. Our study shows that the sources and processes giving rise to haze events in Beijing are variable and seasonally-dependent: (1) in the heating season, SOA formation is driven by oxidation of aromatics from solid fuel combustion, (2) under high NOx and RH conditions, aqueous phase chemistry can be a major contributor to SOA formation.