03 May 2021

03 May 2021

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

Budget of nitrous acid (HONO) and its impacts on atmospheric oxidation capacity at an urban site in the fall season of Guangzhou, China

Yihang Yu1,2,, Peng Cheng1,2,, Huirong Li1,2, Wenda Yang1,2, Baobin Han1,2, Wei Song3, Weiwei Hu3, Xinming Wang3, Bin Yuan4,5, Min Shao4,5, Zhijiong Huang4, Zhen Li4, Junyu Zheng4,5, Haichao Wang6, and Xiaofang Yu1,2 Yihang Yu et al.
  • 1Institute of Mass Spectrometry and Atmospheric Environment, Jinan University, Guangzhou 510632, China
  • 2Guangdong Provincial Engineering Research Center for Online Source Apportionment System of Air Pollution, Guangzhou 510632, China
  • 3State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • 4Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
  • 5Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou 511443, China
  • 6School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, China
  • These authors contributed equally to this work.

Abstract. Nitrous acid (HONO) can produce hydroxyl radicals (OH) by photolysis and plays an important role in atmospheric photochemistry. Over the years, high concentrations of HONO have been observed in the Pearl River Delta region (PRD) of China, which may be one reason for the elevated atmospheric oxidation capacity. A comprehensive atmospheric observation campaign was conducted at an urban site in Guangzhou from 27 September to 9 November 2018. During the period, HONO was measured from 0.02 to 4.43 ppbv with an average of 0.74 ± 0.70 ppbv. The emission ratios (HONO/NOx) of 0.9 ± 0.4 % were derived from 11 fresh plumes. The primary emission rates of HONO at night were calculated to be between 0.04 ± 0.02 ppbv h−1 and 0.30 ± 0.15 ppbv h−1 based on a high-resolution emission inventory. The HONO formation rate by the homogeneous reaction of OH + NO at night was 0.26 ± 0.08 ppbv h−1, which can be seen as secondary results from primary emission. They were both much higher than the increase rate of HONO (0.02 ppbv h−1) during night. Soil emission rate of HONO at night was calculated to be 0.019 ± 0.001 ppbv h−1. Assuming dry deposition as the dominant removal process of HONO at night, and a deposition velocity of at least ~2.5 cm s−1 is required to balance the direct emissions and OH + NO reaction. Correlation analysis shows that NH3 and relative humidity (RH) may participate in the heterogeneous transformation from NO2 to HONO at night. In the daytime, the average primary emission Pemis was 0.12 ± 0.01 ppbv h−1, and the homogeneous reaction POH + NO was 0.79 ± 0.61 ppbv h−1, larger than the unknown sources PUnknown (0.65 ± 0.46 ppbv h−1). These results suggest primary emissions as a key factor affecting HONO at our site, both during daytime and nighttime. Similar to previous studies, the daytime unknown source of HONO, PUnknown, appeared to be related to the photo-enhanced conversion of NO2. The daytime average OH production rates by photolysis of HONO was 3.7 × 106 cm−3 s−1, lower than that from O1D + H2O at 4.9 × 106 cm−3 s−1. Simulations of OH and O3 with the Master Chemical Mechanism (MCM) box model suggested strong enhancement effect of HONO on OH and O3 by 59 % and 68.8 %, respectively, showing a remarkable contribution of HONO to the atmospheric oxidation in the fall season of Guangzhou.

Yihang Yu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-178', Anonymous Referee #1, 21 Jun 2021
  • RC2: 'Comment on acp-2021-178', Anonymous Referee #2, 25 Jun 2021
    • AC2: 'Reply on RC2', YiHang Yu, 09 Aug 2021
    • AC3: 'Reply on RC2', Peng Cheng, 10 Aug 2021

Yihang Yu et al.


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Short summary
The research content of this paper is the budget of nitrous acid (HONO) and its impacts on atmospheric oxidation capacity at an urban site in Guangzhou of China. We conducted a comprehensive atmospheric observation at an urban site in Guangzhou in autumn of 2018. The results further showed that the direct and indirect contributions of primary emission to HONO are great at the site both during daytime and nighttime. And HONO contributed significantly to the atmospheric oxidation of Guangzhou.