Impact of different emission inventories on the tropospheric ozone budget

Abstract

Determining the contributions of emissions to specific trace gas concentrations is essential for assessing anthropogenic influence on climate change. Tropospheric ozone (O3) is an important contributor to climate and air quality. Tropospheric O3 is a greenhouse gas which has increased by 30% since the industrial revolution. Large tropospheric O3 concentrations have a negative impact on human health and vegetation. In addition to natural sources, such as downward transport from the stratosphere, several anthropogenic source categories exist, such as industry and land transport, which are major emission sources of nitrogen oxides (NOx), non-methane hydrocarbons (NMHCs), and carbon monoxide (CO). As precursors of the formation of tropospheric O3, these also indirectly affect air quality. Furthermore, tropospheric O3 is an important source of the hydroxyl radical (OH), which in turn determines the lifetime of greenhouse gases such as methane. Because O3 production is characterized by a high degree of non-linearity, it is not possible to directly derive the amount of O3 produced by emissions from different source categories. Therefore, Chemistry-Climate Model equipped with specific source attribution methods (tagging technique) are used. In this study, the contributions of ten source categories to tropospheric O3 are examined using simulation results from the EMAC (ECHAM5/ MESSy Atmospheric Chemistry) model with diagnostic output of TAGGING Submodel. This technique can be used to trace the complex reaction pathways of species emitted from different sources to O3 formation. The source categories considered are land transport, shipping, aviation, anthropogenic non-traffic, biogenic, biomass burning, lightning, CH4 decomposition, N2O decomposition, and stratospheric O3 production. The data used in the study came from simulations performed for Phases 1 and 2, of the Chemistry-Climate Model Initiative (CCMI). It was found in principle that the lifetime of methane in the EMAC simulations of the CCMI Phase 2 simulation is shorter than in the CCMI Phase 1 simulations. The simulations performed for this study are transient simulations for the period 2000 - 2010. Both simulations are identical except for the emission inventories and ozone-depleting substances. To examine the shorter methane lifetime of the CCMI Phase 2 simulation, this study uses an extended version of a tagging method for OH and HO2 (HOx) that assigns OH mixing ratios to source categories. The diagnosed largest absolute differences in the tropospheric O3 between both simulations, are shown in anthropogenic non-traffic and land transport categories in the northern hemisphere as well as anthropogenic non-traffic, biomass burning and shipping in the southern hemisphere. Consistent with this, the NOx emissions from land