# Unraveling the Drivers of Continuous Summer Ozone Pollution Episodes in Bozhou, China: Toward Targeted Control Strategies

## TL;DR

This study identifies the causes of summer ozone pollution in Bozhou, China, and suggests strategies to reduce it by targeting specific pollutants.

## Contribution

The study provides new insights into the mechanisms of ozone formation in Bozhou and proposes targeted control strategies based on local pollution sources.

## Key findings

- Ozone episodes in Bozhou are mainly driven by high temperatures, low wind speeds, and anthropogenic VOCs like OVOCs and alkanes.
- NOx availability is the primary regulator of ozone formation, with NOx-related reactions dominating radical sinks in the morning.
- OVOC photolysis contributes significantly to radical generation, and selective control of OVOCs and alkenes is recommended to lower ozone levels.

## Abstract

Given the deteriorating situation of ambient ozone (O3) pollution in some areas of China, understanding the mechanisms driving O3 formation is essential for formulating effective control measures. This study examines O3 formation mechanisms and ROx (OH, HO2, and RO2) radical cycling driven by photochemical processes in Bozhou, located at the junction of Jiangsu–Anhui–Shandong–Henan (JASH), a region heavily affected by O3 pollution, by applying a zero-dimensional box model (Framework for 0-Dimensional Atmospheric Modeling, F0AM) coupled with the Master Chemical Mechanism (MCM v3.3.1) and Positive Matrix Factorization (PMF 5.0) to characterize O3 pollution, identify volatile organic compound (VOC) sources, and quantify radical budgets during pollution episodes. The results show that O3 episodes in Bozhou mainly occurred in June under conditions of high temperature and low wind speed. Oxygenated volatile organic compounds (OVOCs), alkanes, and halocarbons were the dominant VOCs groups. The CH3O2 + NO reaction accounted for 24.3% of O3 production, while photolysis contributed 68.7% of its removal. Elevated VOCs concentrations in Bozhou were largely maintained by anthropogenic sources such as vehicle exhaust, solvent utilization, and gasoline evaporation, which collectively enhanced O3 production. The findings indicate that O3 formation in the region is primarily regulated by NOx availability. Therefore, emission reductions targeting NOx, along with selective control of OVOCs and alkenes, would be the most effective strategies for lowering O3 levels. Model simulations further highlight Bozhou’s strong atmospheric oxidation capacity, with OVOC photolysis identified as the dominant contributor to ROx generation, accounting for 33% of the total. Diurnal patterns were evident: NOx-related reactions dominated radical sinks in the morning, while HO2 + RO2 reactions accounted for 28.5% in the afternoon. By clarifying the mechanisms of O3 formation in Bozhou, this study provides a scientific basis for designing ozone control strategies across the JASH junction region. In addition, ethanol was not directly measured in this study; given its potential to generate acetaldehyde and affect local O3 formation, its possible contribution introduces additional uncertainty that warrants further investigation.