Evidence for coordinated control of PM₂.₅ and O₃ : long-term observational study in a typical cty of central plains urban agglomeration

Abstract

Fine particulate matter (PM2.5) and Ozone (O3) pollution have emerged as the primary environmental challenges in China in recent years. Following the implementation of the Air Pollution Prevention and Control Action Plan, a substantial decline in PM2.5 concentrations was observed, while O3 concentrations exhibited an increasing trend across the country. Here, we investigated the long-term trend of O3 from 2015 to 2022 in Xinxiang City, a typical city within the Central Plains urban agglomeration. Our findings indicate that the hourly average O3 increased by 3.41 μg m−3 yr−1, with the trend characterized by two distinct phases (Phase I, 2015–2018; Phase II, 2019–2022). Interestingly, the increasing rate of O3 concentration in Phase I (7.89 μg m−3) was notably higher than that in Phase II (2.89 μg m−3). The Random Forest (RF) model was employed to identify the key factors influencing O3 concentrations during the two phases. The significant dropping of PM2.5 in Phase I could be responsible for the O3 increase. In Phase II, the reductions in nitrogen dioxide (NO2) and unfavorable meteorological conditions were the major drivers of the continued increase in O3. The Observation-Based Model (OBM) was developed to further explore the role of PM2.5 in O3 formation. Our results suggest that PM2.5 can influence O3 concentrations and the chemical sensitivity regime through heterogeneous reactions and changes in photolysis rates. In addition, the relatively high concentration of PM2.5 in Xinxiang City in recent years underscores its significant role in O3 formation. Future efforts should focus on the joint control of PM2.5 and O3 to improve air quality in the Central Plains urban agglomeration.