Influence of nitrogen oxides and volatile organic compounds emission changes on tropospheric ozone variability, trends and radiative effect

Abstract

Ozone in the troposphere is a prominent pollutant whose production is sensitive to the emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). Here, we assess the variation of tropospheric ozone levels, trends, ozone photochemical regimes and radiative effects using the ECHAM6–HAMMOZ chemistry–climate model for the period 1998–2019 and satellite measurements. The global mean simulated trend in tropospheric column ozone (TRCO) for the study period (1998–2019) is 0.89 ppb decade−1. During the overlapping period with Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) observations (2005–2019), the simulated global mean TRCO trends (1.58 ppb decade−1) show fair agreement with OMI/MLS estimates (1.4 ppb decade−1). The simulations for doubling emissions of NOx (DoubNOx), VOCs (DoubVOC), and halving emissions of NOx (HalfNOx) and VOCs (HalfVOC) show nonlinear responses to ozone trends and tropospheric ozone photochemical regimes. The DoubNOx simulations show VOC-limited regimes over the Indo-Gangetic Plain, eastern China, western Europe and the eastern US, while HalfNOx simulations show NOxlimited regimes over North America and Asia. Emissions changes in NOx (DoubNOx/HalfNOx) influence the shift in tropospheric ozone photochemical regimes compared to VOCs (DoubVOC/HalfVOC). The estimated global mean TO3RE during 1998–2019 from the control (CTL) simulations is 1.21 W m−2. The global mean TO3RE shows enhancement by 0.36 W m−2 in DoubNOx simulations compared to CTL. While TO3RE shows a reduction in other simulations compared to CTL (DoubVOC: −0.005 W m−2, HalfNOx: −0.12 W m−2 and HalfVOC: −0.03 W m−2). We show that emission changes in anthropogenic NOx cause more significant changes in TO3RE than anthropogenic VOCs.