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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  18 May 2020

18 May 2020

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A revised version of this preprint is currently under review for the journal ACP.

Seasonal variations in the high time-resolved aerosol composition, sources, and chemical process of background submicron particles in North China Plain

Jiayun Li1,4, Liming Cao2, Wenkang Gao1, Lingyan He2, Yingchao Yan1,4, Dongsheng Ji1, Zirui Liu1, and Yuesi Wang1,3,4 Jiayun Li et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen, 518055, China
  • 3Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 4University of Chinese Academy of Sciences, Beijing 100049, China

Abstract. For the first time in the North China Plain (NCP), we investigated the seasonal variations of submicron particles (NR-PM1) and its chemical composition at a background mountain station using Aerodyne high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). The averaged NR-PM1 were highest in autumn (15.1 μg m−3) and lowest in summer (12.4 μg m−3), with the abundance of more nitrate in spring (34 %), winter (31 %), and autumn (34 %), and elevated organics (40 %) and sulfate (38 %) proportion in summer. The submicron particles were almost neutralized by excess ammonium in all four seasons except summer, when the aerosol particles appeared to be slightly acidic. The size distribution of all PM1 species showed a consistent accumulation mode peaked at approximately 600–800 nm (dva), indicating the highly aged and internally mixed nature of the background aerosols, which further supported by the source appointment using multilinear engine (ME-2) and significant contributions of aged secondary organic aerosol (SOA) in organic aerosol (OA) were resolved in all seasons (> 77 %), especially in summer (95 %). The oxidation degree and evolution process of OAs in the four seasons were further investigated, and enhanced carbon oxidation state (−0.45–0.10), O / C (0.54–0.75) and OM / OC (1.86–2.13) ratios compared with urban studies were observed, with the highest oxidation degree of which appeared in summer, likely due to the relatively stronger photochemical processing which dominated the processes of both less oxidized OA (LO-OOA) and more oxidized OA (MO-OOA) formations. Aqueous-phase processing also contributed to the SOA formation but prevailed in autumn and winter and the role of which to MO-OOA and LO-OOA also varied in different seasons. In addition, compared with the urban atmosphere, LO-OOA formation in the background atmosphere exhibited more regional characteristics, as photochemical and aqueous-phase processing enhanced during the transport in summer and autumn, respectively. Furthermore, the backward trajectories analysis showed that higher submicron particles were associated with air mass for short distance transported from the southern regions in four seasons, while the long-range transport from Inner Mongolia (west and north regions) also contributed to the summer particle pollutions in the background areas of NCP. Our results illustrate the background particles in NCP are influenced significantly by aging processing and transport, and the more neutralized state of submicron particles with the abundance of nitrate compared with those in the background atmosphere in southern and western China, highlighting the regional reductions in emissions of nitrogen oxide and ammonia are critical for remedying the increased occurrence of nitrate-dominated haze event in the NCP.

Jiayun Li et al.

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Short summary
For the first time, we investigated the highly time-resolved chemical characterization, sources, and evolution of atmospheric submicron aerosols at a regional background site in the North China Plain (NCP) using an Aerodyne high-resolution time-of-flight aerosol mass spectrometry, and evaluated the seasonal differentials of photochemical and aqueous-phase processing on SOA composition and oxidation degree of OA. The results will help to understand air pollution in the NCP on a regional scale.
For the first time, we investigated the highly time-resolved chemical characterization, sources,...