Research on the characteristics and triggering factors of concurrent events of ozone pollution and nocturnal ozone increase in Xinxiang, China

Abstract

In recent years, the phenomenon of nocturnal ozone increase (NOI) has become increasingly common worldwide. The occurrence of such events can potentially enhance the risk of ozone pollution, but the connection between NOI events and ozone pollution remains poorly understood. Based on ground observations, ERA5 dataset and air quality models (CMAQ and CAMx), this study investigates the characteristics of ozone pollution and NOI concurrent events in Xinxiang, China from 2017 to 2021, and qualitatively and quantitatively analyzes the triggering factors on a typical persistent concurrent event (PCE, June 13–20, 2017). We identify the relationship between summer ozone pollution and NOI events. On ozone pollution days, NOI is more prone to occur (incidence: 46.8 %). At the same time, the occurrence of NOI events tends to cause a higher ozone base in the morning from 04:00 to 10:00 local time (LT, 9.12–16.20 μg m⁻³ higher than that of non-NOI days), promoting the emergence of ozone pollution. During PCE, for all NOI events (12 times) and ozone pollution, vertical diffusion (VDIF) is the primary trigger, followed by regional transport from the latitudinal (north-south) direction (YADV), which is mainly distributed in central and southern Henan (especially Zhengzhou). Additionally, local emissions from industry and transportation also have a significant influence on ozone levels in Xinxiang. This study identifies the characteristics and relationship between NOI events and ozone pollution, and reveals the formation mechanism of PCE, which provides new insights into NOI research and will promote local ozone pollution prevention and control.