ENSO modulation of summertime tropospheric ozone over China

Abstract

Ozone (O _3 ) is one of the most critical pollutants affecting air quality in China in recent years. In this study, different impacts of the El Niño–Southern Oscillation (ENSO) warm/cold phases on summertime tropospheric O _3 over China are examined based on model simulations, ground measurements, and reanalysis data. Summertime surface O _3 concentrations in China show a positive correlation with ENSO index during years 1990–2019, with the largest increases by 20% over southern China in El Niño (warm phase) relative to La Niña (cold phase) years. The ENSO modulation extends to the middle and even upper troposphere. Our analysis indicates that O _3 flux convergence associated with weakened southerlies is the primary reason for the increase in tropospheric O _3 over southern China. In addition, the O _3 increase during El Niño years is mainly from domestic emissions in China. This study highlights the potential significance of ENSO in modulating tropospheric O _3 concentrations in China, with great implications for O _3 pollution mitigation.

Keywords

• O3
• China
• El Niño
• ENSO