Ozone response to precursors changes in the Chengdu-Chongqing economic circle, China, from satellite and ground-based observations

Jie Ren; Yufang Hao; Xudong Zheng; Xin Li; Shaodong Xie

doi:10.1016/j.scitotenv.2024.176037

Ozone response to precursors changes in the Chengdu-Chongqing economic circle, China, from satellite and ground-based observations

Sci Total Environ. 2024 Nov 25:953:176037. doi: 10.1016/j.scitotenv.2024.176037. Epub 2024 Sep 3.

Authors

Jie Ren¹, Yufang Hao², Xudong Zheng¹, Xin Li¹, Shaodong Xie³

Affiliations

¹ College of Environmental Sciences and Engineering, State Key Joint Laboratory of Environmental Simulation and Pollution Control, Peking University, Beijing 100871, China.
² College of Environmental Sciences and Engineering, State Key Joint Laboratory of Environmental Simulation and Pollution Control, Peking University, Beijing 100871, China; Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, -PSI, Switzerland.
³ College of Environmental Sciences and Engineering, State Key Joint Laboratory of Environmental Simulation and Pollution Control, Peking University, Beijing 100871, China; Tianfu Yongxing Laboratory, Chengdu 610213, Sichuan, China. Electronic address: sdxie@pku.edu.cn.

PMID: 39236828
DOI: 10.1016/j.scitotenv.2024.176037

Abstract

Ozone (O₃) pollution has become a noticeable problem in the Chengdu-Chongqing Economic Circle in China. The April-September MDA8 O₃ level increases significantly by 2.26 μg m^-3 year^-1 from 2015 to 2023, with meteorological factors occupying merely 18 % in line with multivariate linear regression. To reveal the impact of anthropogenic emissions on O₃ increase, O₃ production sensitivity is accurately diagnosed by deriving localized thresholds for satellite formaldehyde (HCHO) to NO₂ ratio and validated by in-situ measurements and observation-based model. Tracking volatile organic compounds (VOCs) and NOx through satellite HCHO and NO₂, the O₃ responses to precursor changes are assessed for long-term and special cases, and appropriate precursor reduction ratios are inferred. The results present that the transition range of satellite HCHO/NO₂ from VOC-limited to NOx-limited in the region ranges from 2.7 to 4.3. The VOC-limited regime is concentrated in the urban areas of Chongqing and Chengdu as well as the central of the neighboring cities such as Deyang, Mianyang, and Meishan. The relative incremental reactivity from in-situ observations and box model at three sites in August 2019 demonstrates that O₃ is most sensitive to anthropogenic VOC at urban and suburban sites, consistent with satellite results. Satellite and surface NO₂ decrease at an annual rate of -2.1 % and - 2.9 % between 2015 and 2023, with larger decreases in Chengdu and Chongqing. In contrast, the trend of satellite HCHO is insignificant, indicating effective reduction in NOx but no significant reduction in VOC. This inappropriate reduction results in an increase in urban O₃. The three short-term cases further validate the need for synergistic NOx and VOC reductions. Based on the relationship between O₃ and satellite NO₂ and HCHO, the minimum and optimal reduction ratios of VOC to NOx are 0.4:1 and 2.4:1 for the entire region, with higher ratios in Chengdu and Chongqing.

Keywords: Formaldehyde-to-NO(2) ratio; Nitrogen oxide; O(3) sensitivity; Ozone pollution; RIR; Volatile organic compounds.