22 Jul 2022
22 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Examining the implications of photochemical indicators on the O3-NOx-VOC sensitivity and control strategies: A case study in the Yangtze River Delta (YRD), China

Xun Li1, Momei Qin1, Lin Li1, Kangjia Gong1, Huizhong Shen2, Jingyi Li1, and Jianlin Hu1 Xun Li et al.
  • 1Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science and Technology, Nanjing 210044, China
  • 2School of Environmental Sciences and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China

Abstract. Ozone (O3) has become a significant air pollutant in China in recent years. O3 abatement is challenging due to the nonlinear response of O3 to precursors nitrogen oxides (NOx) and volatile organic compounds (VOCs). Photochemical indicators are widely used to estimate the O3-NOx-VOC sensitivity, and this has important policy implications. However, the effectiveness of the indicators has seldom been evaluated. This study examines the applications of four indicators that include the ratio of the production rates of H2O2 and HNO3 (PH2O2 / PHNO3), HCHO / NO2, HCHO / NOy, and reactive nitrogen (NOy) in the Yangtze River Delta (YRD) with localized thresholds. The overall accuracy was high (> 92 %) for all indicators and not significantly reduced with different simulation periods or in different locations of the region. By comparing with the O3 isopleths, it was found that HCHO/NO2 and HCHO / NOy showed the most consistency, whereas PH2O2 / PHNO3 (NOy) tended to underestimate (overestimate) the positive response of O3 to NOx. Additionally, PH2O2 / PHNO3 was less likely to attribute the O3 formation to mixed sensitivity than the other indicators, and this demonstrated a preference for a single-pollutant control strategy. This study also revealed that the details in the methodology used to derive the threshold values impacted the results, and this may produce uncertainties in the application of photochemical indicators.

Xun Li et al.

Status: open (until 02 Sep 2022)

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Xun Li et al.


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Short summary
Photochemical indicators have been widely used to predict O3-NOx-VOC sensitivity with given thresholds. We assessed the effectiveness of four indicators with a case study in the Yangtze River Delta, China. The overall performance was good. However, some indicators showed inconsistencies with the O3 isopleths. The methodology used to determine the thresholds may produce uncertainties. These results improve our understanding of the use of photochemical indicators in policy implications.