[Analysis of Ozone Pollution and Precursor Control Strategies in the Pearl River Delta During Summer and Autumn Transition Season].

Abstract

To analyze the causes of ozone pollution in the Pearl River Delta （PRD） Region during the summer and autumn transition seasons, a case study was carried out in Guangzhou, which is located in the center of the PRD Region, to analyze the ozone photochemical production and destruction pathways as well as emission reduction scenarios using a box model based on comprehensive observation. The results showed that the stagnant meteorological conditions and high temperature during the observation period were suitable for the photochemical production of ozone, which led to widespread and prolonged ozone pollution. Aromatic hydrocarbons （AHs） contributed the most to the ozone formation potential （OFP）, and m/p-xylene, toluene, and o-xylene were the major three VOC species contributing to the OFP. Box model analysis revealed that the averaged net O₃ production rate during the polluted period was 23.2×10^-9 h^-1 and the peak reached 39.2×10^-9 h^-1. The HO₂·+NO and NO₂+·OH reaction pathways contributed the most to the local photochemical ozone production （51.2%） and destruction （47.0%）, respectively. Observed ozone concentration was primarily controlled by both the local photochemical O₃ production and the export-dominated transport. The RIR and EKMA analyses showed that O₃ formation in Guangzhou during the summer-autumn transition seasons was mainly a VOC-limited regime and AHs showed the greatest sensitivity to O₃ production. Toluene, m/p-xylene, o-xylene, n-butane, and propylene were the five key components affecting O₃ generation. The analysis of reduction scenarios showed that reducing anthropogenic VOC emissions was the most favorable way to reduce O₃ concentrations； however, if NO_x emission was controlled after reducing VOCs, the O₃ concentration would rebound in a short time. Our results suggested that the synergistic reduction of VOCs and NO_x while mainly focusing on VOCs alleviation should be implemented to continuously reduce ozone concentrations in the future.