Understanding the effects of International Shipping NOx Emissions on Global Surface Ozone Concentrations based on Global Model Calculations using three different approaches

Abstract

Tropospheric ozone is an important air pollutant and greenhouse gas. One of the major sources of tropospheric ozone is the photochemical production from precursors: oxides of nitrogen (NO and NO2, collectively NOx) and volatile organic compounds (VOC), including methane. Emissions from international shipping are increasingly recognized as an important source of air pollution and subsequently impact human health. Emissions of NOx from ships can influence the surface ozone concentrations in various ways depending on location and time of year. In this study model results investigating the influence of shipping emissions on ozone from three global models are compared: two using tagging methods, and one using a perturbation method. CAM-Chem: Simulations are performed for the 2000-2018 historical period using the CAMS-GLOB emissions which employ the NOx-tagging technique (summarized in Butler et al. 2020). Here the simulated surface ozone is labelled with the sea-area (see figure) from which it’s precursor NOx molecule is emitted. EMAC: Same as CAM-Chem. Employs the combinatorial tagging technique (summarized in Grewe et al. 2017), considering NOx and VOC simultaneously. The same source regions as in CAM-Chem are applied. EMEP: Simulations are performed for the years 2010 and 2018 which employ a perturbation of shipping NOx emissions (summarized in Jonson et al. 2020) (same emissions as above models). Here, two separate simulations are performed: (i) Baseline ship NOx emissions for the given year, and (ii) Ship NOx from a given sea-area (see figure) reduced by 15 % compared to the baseline emissions for the year. The difference in simulated surface ozone between these two simulations would indicate the impact of emission reduction at that sea-area. Tagging approach enables direct attribution to source region while perturbation explains the impacts of regional mitigation options (or emission changes). The main pros and cons of these approaches, and various results from these simulations will be presented.