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 (VOC). In this study, 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) during 1998–2019 is 0.89 ppb decade⁻¹. The simulated global mean TRCO trends (1.58 ppb decade⁻¹) show fair agreement with OMI/MLS (2005–2019) (1.4 ppb decade⁻¹). The simulations for doubling emissions of NOx (DNOx), VOCs (DVOC), halving of emissions NOx (HNOx) and VOCs (HVOC) show nonlinear responses to ozone trends and tropospheric ozone photochemical regimes. The DNO_X simulations show VOC–limited regimes over Indo-Gangetic Plains, Eastern China, Western Europe, and the eastern US, while HNOx simulations show NOx–limited regimes over America and Asia. Emissions changes in NOx (DNOx/HNOx) influence the shift in tropospheric ozone photochemical regimes compared to VOCs (DVOC/HVOC).

Further, we provide estimates of tropospheric ozone radiative effects (TO3RE). The estimated global mean TO3RE during 1998–2019 from the CTL simulations is 1.21 W m⁻². The global mean TO3RE shows enhancement by 0.36 W m⁻² in DNOx simulations than CTL. While TO3RE shows reduction in other simulations compared to CTL (DVOC: by -0.005 W m⁻²; HNOx: by -0.12 W m⁻²; and HVOC: by -0.03 W m⁻²). The impact of anthropogenic NOx emissions is higher on TO3RE than VOCs emissions globally.