23 Jun 2021

23 Jun 2021

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

Measurement report: Fast photochemical production of peroxyacetyl nitrate (PAN) over the rural North China Plain during cold-season haze events

Yulu Qiu1,2,3,4, Zhiqiang Ma1,3,4, Ke Li5, Mengyu Huang6, Jiujiang Sheng6, Ping Tian6, Jia Zhu2, Weiwei Pu3,4, Yingxiao Tang7, Tingting Han3,4, Huaigang Zhou3,4, and Hong Liao2 Yulu Qiu et al.
  • 1Institute of Urban Meteorology, China Meteorological Administration, Beijing, 100089, China
  • 2Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing, 210044, China
  • 3Beijing Shangdianzi Regional Atmosphere Watch Station, Beijing, 101507, China
  • 4Environmental Meteorology Forecast Center of Beijing-Tianjin-Hebei, Beijing, 100089, China
  • 5John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
  • 6Beijing Weather Modification Office, Beijing, 100089, China
  • 7Tianjin Environmental Meteorology Center, Tianjin, 300074, China

Abstract. Photochemical pollution over the North China Plain (NCP) are attracting considerable concern. Peroxyacetyl nitrate (PAN) is usually viewed as the second most important photochemical pollutant featuring high mixing ratios during warm seasons. Our observations at a background site in the NCP identified high PAN concentrations even during cold-season haze events. The abrupt increasing rates of PAN by 244 % and 178 % over the morning hours (8:00–12:00) on 10/20 and 10/25, 2020 were 10.6 and 7.7 times those on clean days. The pollution days were characterized by higher temperature and humidity, accompanied by anomalous southerlies. Enhanced local photochemistry has been identified as the dominant factor that controls PAN increase in the morning at the rural site, as the time when prevailing wind turned to southerlies was too late to facilitate direct transport of PAN from the polluted urban region. By removing the effect of direct transport of PAN, we provide a quantitative assessment of net PAN chemical production rate of 0.45 ppb h−1 on the polluted morning, also demonstrating the strong local photochemistry. Using observations and calculated photolysis rates, we find that oxidation of acetaldehyde by hydroxyl radical (OH) is the primary pathway of peroxyacetyl radical formation at the rural site. Acetaldehyde concentrations and production rates of HOx (HOx = OH + HO2) radical on pollution days were 2.8 and 2 times that on clean days, respectively, leading to the abrupt increase of PAN in the morning. Formaldehyde (HCHO) photolysis dominates the daytime HOx production thus contributing to fast photochemistry of PAN. Our observational results fully explain the cause of rapid increase of PAN during cold days at a rural site of the NCP, as well as provide the evidence of important role of HCHO photolysis in secondary pollutants at lower nitrogen oxide emissions. This highlights the imperative to implement strict volatile organic compounds controls out of summer seasons over the NCP.

Yulu Qiu et al.

Status: open (until 05 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-359', Anonymous Referee #1, 14 Jul 2021 reply
  • RC2: 'Comment on acp-2021-359', Anonymous Referee #2, 16 Jul 2021 reply

Yulu Qiu et al.


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Short summary
Photochemical pollution over the North China Plain (NCP) are attracting much concern. Our observations at a rural site in the NCP identified high peroxyacetyl nitrate (PAN) concentrations even during cold days. Increased acetaldehyde concentration and hydroxyl radical production rate drive fast PAN formation. Moreover, our study emphasizes the importance of formaldehyde photolysis in PAN formation, and calls for implementing strict volatile organic compound controls out of summer over the NCP.