Abstract
Abstract. Anthropogenic and natural emissions influence the tropospheric ozone budget, thereby affecting air quality and climate. To study the influence of different emission sources on the ozone budget, often source apportionment studies with a tagged tracer approach are performed. Studies investigating air quality issues usually rely on regional models with a fine spatial resolution, while studies focusing on climate-related questions often use coarsely resolved global models. It is well known that simulated ozone mixing ratios depend on the resolution of the model and the resolution of the emission inventory. Whether the contributions simulated using source apportionment approaches also depend on the model resolution, however, is still unclear. Therefore, this study attempts for the first time to analyse the impact of the model, the model resolution, and the emission inventory resolution on simulated ozone contributions using a diagnostic tagging method. The differences in the ozone contributions caused by these factors are compared with differences that arise from the usage of different emission inventories. To do so, we apply the MECO(n) (MESSy-fied ECHAM and COSMO models nested n times) model system which couples online a global chemistry-climate model with a regional chemistry-climate model equipped with a tagging scheme for source apportionment. The results of the global model (at 300 km horizontal resolution) are compared with the results of the regional model at 50 km (Europe) and 12 km (Germany) resolutions. Besides model-specific differences and biases that are discussed in detail, our results have important implications for other modelling studies and modellers applying source apportionment methods. First, contributions from anthropogenic emissions averaged over the continental scale are quite robust with respect to the model, model resolution, and emission inventory resolution. Second, differences on the regional scale caused by different models and model resolutions can be quite large, and regional models are indispensable for source apportionment studies on the subcontinental scale. Third, contributions from stratospheric ozone transported to the surface differ strongly between the models, mainly caused by differences in the efficiency of the vertical mixing. As stratospheric ozone plays an important role for ground level ozone, but the models show large differences in the amount of downward transported ozone, source apportionment methods should account for this source explicitly to better understand inter-model differences.
Highlights
We are focusing on the question: are contributions of emissions to ozone a matter of scale? To answer this question we compare the influences of the model, the model resolution, the emission resolution, and the emission inventory on the results of ozone contribution analyses
By applying the identical tagging diagnostics in the regional and global model with consistent boundary conditions, we are able to compare the results of model instances with different resolutions to investigate the influence of the model and emission inventory resolutions onto the diagnosed ozone contributions
For the specific model set-up involving the global model EMAC and the regional model COSMO-CLM/Modular Earth Submodel System (MESSy) our results show that simulated differences in ozone contribuwww.geosci-model-dev.net/13/363/2020/
Summary
Emissions from land transport, industry, and shipping contribute largely to global budgets of trace gases like NOx and O3, thereby impacting air quality and climate (e.g. Eyring et al, 2007; Matthes et al, 2007; Hoor et al, 2009; Fiore et al, 2012; Young et al, 2013; Hendricks et al, 2017; and Mertens et al, 2018). Wild and Prather, 2006; Wild, 2007; Tie et al, 2010; Holmes et al, 2014; and Markakis et al, 2015), the impact of the third factor – the model and emission inventory resolutions – on the simulated contributions of specific emission sources to ozone has not yet been systematically investigated in detail. Dunker et al, 2002; Li et al, 2012; Kwok et al, 2015; Valverde et al, 2016; and Karamchandani et al, 2017) It is unclear if the results from global and regional models are comparable and how large potential errors, caused by the coarse resolution of global models, are. We investigate the influences of four different modelling aspects on source apportionment results for ozone; these aspects are as follows:
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