A global climate simulation is performed with the ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry climate model. EMAC is a numerical chemistry and climate simulation system that includes submodels describing tropospheric and middle atmosphere processes and their interaction with oceans, land and human influences (Jöckel et al., 2010). It uses the second version of the Modular Earth Submodel System (MESSy2.53) to link multi-institutional computer codes. The core atmospheric model is the 5th generation European Centre Hamburg general circulation model (ECHAM5; Roeckner et al., 2006). For the present study we apply EMAC in the T42L90MA resolution, i.e. with a spherical truncation of T42 (corresponding to a quadratic Gaussian grid of approx. 2.8° by 2.8° in latitude and longitude) with 90 vertical hybrid pressure levels up to 0.01 hPa. For the simulation presented in this study, the time span of July 2007 to December 2008 is considered: half a year as a spin-up and 1 year for the analysis.
For the chemical scheme, we use the submodel MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere), which is based on Sander et al. (2011) and Jöckel et al. (2010). The chemical mechanism includes 218 gas-phase, 12 heterogeneous and 68 photolysis reactions. In total 188 species are considered. It regards the basic chemistry of OH, HO2, O3, CH4, nitrogen oxides, alkanes, alkenes, chlorine and bromine. Alkynes, aromatics and mercury are not considered.
Total global emissions of lightning NOx are scaled to approximately 4 Tg(N) a−1 (parameterized according to Grewe et al., 2001). The submodel ONEMIS (Kerkweg et al., 2006) calculates NOx emissions from soil (parameterized according to Yienger and Levy, 1995) and biogenic C5H8 emissions (parameterized according to Guenther et al., 1995). Direct CH4 emissions are not considered, and instead pseudo-emissions are calculated using the submodel TNUDGE (Kerkweg et al., 2006). This submodel relaxes the mixing ratios in the lowest model layer towards observations by Newtonian relaxation (more details are given by Jöckel et al., 2016).
The simulation is based on the quasi chemistry-transport model (QCTM) mode in which the chemistry is decoupled from the dynamics (Deckert et al., 2011). The anthropogenic emissions are taken from the MACCity emission inventory (Granier et al., 2011). The TAGGING submodel (as described by Grewe et al., 2017) is coupled to the detailed chemical solver MECCA from which it obtains information about tracer concentrations and reaction rates. Based on this information, it calculates the contributions of source categories to O3, CO, NOy, PAN and NMHC concentrations. The contributions of OH and HO2 are calculated with the advanced method V1.1. The implementation is based on MESSy2.53 and available in MESSy2.54.
The second simulation is the same as the first, except that the rest terms are neglected in the TAGGING submodel.