1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
2Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science & Technology, Nanjing 210044, China
3School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 510275, China
4State Environmental Protection Key Laboratory of Formation and Prevention of the Urban Air Complex, Shanghai Academy of Environmental Sciences, Shanghai, 200223, China
5Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, China
anow at: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
2Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science & Technology, Nanjing 210044, China
3School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 510275, China
4State Environmental Protection Key Laboratory of Formation and Prevention of the Urban Air Complex, Shanghai Academy of Environmental Sciences, Shanghai, 200223, China
5Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, China
anow at: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
Received: 07 Aug 2022 – Discussion started: 12 Aug 2022
Abstract. Particulate nitrate (NO3-) is the one of the dominant components of fine particles in China, especially during pollution episodes, and has a significant impact on human health, air quality and climate. Here a comprehensive field campaign which focus on the atmospheric oxidation capacity and aerosol formation, and their effects in Yangtze River Delta (YRD) had been conducted from May to June, 2019 at a regional site in Changzhou, Jiangsu province in China. The concentration of NO3-, OH radical, N2O5, NO2, O3 and relevant parameters were measured simultaneously. We showed a high NO3- mass concentration with 10.6 ± 8.9 μg m-3 on average, which accounted for 38.3 % of water-soluble components and 32.0 % total PM2.5, and followed by the proportion of sulfate, ammonium and chloride by 26.0 %, 18.0 % and 2.0 %, respectively. This result confirmed the heavy nitrate pollution in eastern China not only happened in winter but also summer time. High nitrate oxidation ratio (NOR) during this study emphasizes the fast nitrate formation capacity in YRD. It is found that OH + NO2 at daytime dominates nitrate formation on clean days while N2O5 hydrolysis largely enhanced and become comparable with that of OH + O2 during polluted days (47.1 % and 52.9 %). An updated observed-constrain Empirical Kinetic Modeling Approach (EKMA) was used to assess the kinetic controlling factors of both local O3 and NO3- productions, which indicated that O3-targeting scheme (VOCs: NOx = 2:1) is effective to mitigate the O3 and nitrate pollution coordinately during summertime in this region. Our results promote the understanding of nitrate pollution mechanisms and mitigation based on field observation and model simulation, and call for more attentions to nitrate pollutions in summertime.
This study investigates the characteristics of particulate nitrate formation and its precursors based on a field campaign in the eastern China. It provides valuable data sets, including measurements of in-situ OH, N2O5 and other relevant parameters, for analyzing summertime nitrate formation, which still needs more elaborated research. The relative importance of daytime and nighttime pNO3- chemical formation pathways was determined, and the response of O3 and pNO3- to precursors reduction was calculated by a box model. The results improve the knowledge on occurrence of summertime nitrate pollution in China. Overall, this work is well organized, while some clarifications are still needed. I recommend publication of this paper in Atmospheric Chemistry and Physics and I have following comments for the authors to consider.
Major comments:
As is indicated by the authors in section 3.3, the N2O5 uptake coefficient could vary within a large range. Using a constant coefficient for the whole campaign seems to be less convincing, although 0.035 was a reasonable value in this area. I suggest to perform some uncertainty tests or at least choose different coefficient for clean days and polluted days, respectively, as the aerosol composition and water content were not supposed to be the same
Please explain the reason for the significant difference between gamma_s and gamma_p. And then, it would be reasonable for the authors to used gamma_p for the following calculation fo pNO3-.
Specific comments:
Line 88: What does the ‘impact factor’ represent? I found that the authors intended to investigate the controlling factors of nitrate formation rather than its impacts in section 3.4.
Line 194: Please change ‘since’ to ‘due to’.
Line 240~241: Please change ‘appeal’ to ‘appear’.
Line 276~279: Is there any evidences from the campaign or references to support this conclusion?
Table 2: The max and min values of both SOR and NOR are in wrong position for this work.
Particulate nitrate is a growing issue in the air pollution. Based on a comprehensive field measurement, we show a heavy nitrate pollution in eastern China in summer. OH reacts with NO2 at daytime dominates nitrate formation on clean days while N2O5 hydrolysis largely enhanced and become comparable with that of OH reacts with O2 during polluted days (47.1 % and 52.9 %). Model simulation indicates that VOCs: NOx = 2:1 is effective to mitigate the O3 and nitrate pollution coordinately.
Particulate nitrate is a growing issue in the air pollution. Based on a comprehensive field...
