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https://doi.org/10.5194/acp-2020-880
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-880
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Sep 2020

10 Sep 2020

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This preprint is currently under review for the journal ACP.

Exploration of the atmospheric chemistry of nitrous acid in a coastal city of southeastern China: Results from measurements across four seasons

Baoye Hu1,2,3, Jun Duan4, Youwei Hong1,2, Lingling Xu1,2, Mengren Li1,2, Yahui Bian1,2, Min Qin4, Wu Fang4, Pinhua Xie1,3,4,5, and Jinsheng Chen1,2 Baoye Hu et al.
  • 1Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 2Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 3University of Chinese Academy of Sciences, Beijing 100086, China
  • 4Key Laboratory of Environment Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, China
  • 5School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei, 230026, China

Abstract. Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.64 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO2 to HONO in the nighttime was the highest in summer due to water droplets was evaporated under the condition of high temperatures. Based on a budget analysis, the rate of emission from unknown sources (Runknown) was highest at midday, with values of 14.78 ppb h−1 in summer, 6.49 ppb h−1 in autumn, and 2.18 ppb h−1 in spring. Unknown sources made up the largest proportion of all sources in summer (84.92 %), autumn (80.29 %), and spring (49.98 %), whereas the main source in winter was the homogeneous reaction of NO with OH (56.15 %), due to winter having the highest NO concentration of the four seasons. The value of Runknown had a positive logarithmic relationship with the photolysis of particulate nitrate in spring, summer, and autumn. However, Runknown was limited by particulate acidity under the condition of photolysis of particulate nitrate (J (NO3_R) × pNO3) > 1 µg m−3 s−1 in autumn and J(NO3_R) × pNO3 > 2 µg m−3 s−1 in spring and summer. The variation of HONO at night can be exactly simulated based on the HONO / NOx ratio, while the main sources should be considered for daytime simulations. Compared with O3 photolysis, HONO photolysis has long been an important source of OH, particularly in the morning in spring and winter and around noon in summer and autumn. This study draws a full picture of the sources of HONO across all four seasons and improves the comprehension of HONO chemistry in southeastern coastal China.

Baoye Hu et al.

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Short summary
There has been a lack of research into HONO in coastal cities with low concentrations of NOx and PM2.5, but strong sunlight and high humidity. Insufficient research on coastal cities with good air quality has resulted in certain obstacles to assessing the photochemical processes in these areas. Furthermore, HONO contributes to the atmospheric photochemistry depending on the season. Therefore, observations of HONO across four seasons in the southeastern coastal area of China are urgently needed.
There has been a lack of research into HONO in coastal cities with low concentrations of NOx and...
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