Comprehensively exploring the characteristics and meteorological causes of ozone pollution events in Beijing during 2013–2020

Abstract

Ozone (O3) pollution deteriorated in recent years in Beijing; however, the evolution characteristics and formation mechanism of O3 pollution events (OPEs) lack comprehensive exploration from a long-term perspective. Based on 35-site (Beijing) and multi-city (North China) O3 and meteorological monitoring and reanalysis data, totally 61 OPEs during 2013–2020 were counted in Beijing to reveal their characteristics, the relationship with regional pollution, and meteorological causes. Mild, moderate, and heavy pollution in all OPEs (203 ± 28 μg/m3 for averaged MDA8 O3) accounted for 68.4%, 27.8%, and 3.8% of 291 days, respectively. 78.7% of OPEs were concentrated in May–July. The averaged MDA8 O3 concentration, total days and durations of OPEs increased notably from 2013 to 2020, with a rate of 1.6 μg/m3/yr, 2.7 d/yr, and 0.2 d/yr, respectively. Overall, 90% (53%) of OPEs in Beijing co-occurred with regional pollution covering Beijing-Tianjin-Hebei (North China) under the predominant southerly airflow. Meteorological causes of different levels and spatial distribution of OPEs were explored through multi-scale weather processes. The increasing proportion of southwesterly-westerly synoptic circulation (49%–80%) and mountain-valley breeze (51%–70%), along with enhanced temperature, UV radiation, southerly wind, and temperature inversion and decreased relative humidity, collectively contributed to elevated levels of OPEs. The aforementioned meteorological condition facilitated O3 photochemical reactions, the transport of pollutants, and hindered diffusion. Three spatial types (urban, northern and southern suburban pollution) of OPEs were determined by the intensity and direction of southerly wind. Additionally, daytime O3 pollution elevated the mean peak O3 of nocturnal O3 enhancement events (NOEs) by 31 μg/m3 (41%) mainly induced by convective storms and low-level jets. Our comprehensive investigations of OPEs provide important scientific basis for the precise prediction and control of O3 pollution in Beijing.