Ozone Source Apportionment with a Tagging Approach in the LOTOS-EUROS Model

As the majority of the population is exposed to air pollutant levels above the WHO guidelines, poor air quality remains one of the key challenges to increase human wellbeing in Europe. To further improve the ambient air quality it is important to know the extent to which the different anthropogenic activities contribute to the population exposures of particulate matter, nitrogen oxides and ozone. Source attribution is a process of tracing pollution levels back to its origin. Within the LOTOS-EUROS chemistry transport model a labelling technique has been developed and applied extensively for particulate matter and nitrogen oxides. So far, ozone source apportionment was not available.The existing labelling approach was extended for ozone inspired by the implementation of the TOAST module in WRF-CHEM (Lupascu and Butler, 2019). We implemented an additional labelling family for the Ox family. For all reactions in which NO is oxidized to NO2 by a peroxide (RO2 or HO2) the NO2 produced in the Ox family receives the origin of the NO from the NOy family. By capitalizing on the existing labelling modules of LOTOS-EUROS we benefit from the more efficient implementation than simply increasing the number of tracers in the chemical mechanism. The new implementation was applied for the year 2019 by adopting zooming approach with a European domain and a higher resolution nest across northwestern Europe. Evaluation against measurements shows that the model is well capable to reproduce the observed variability across the country. During winter time in northwestern Europe the regional background ozone levels are largely determined by influx from the hemispheric background. Regional production from road transport and other combustion sources are important from July to September, whereas increased levels during spring show considerable contributions from ozone formed in southern Europe. To investigate in how far two modelling systems agree or deviate from each other in terms of source apportionment, simulations with LOTOS-EUROS and WRF-CHEM with a consistent model setup and labelling strategy were performed. The results of this analysis will also be shown at the meeting. Lupaşcu, A. and Butler, T.: Source attribution of European surface O3 using a tagged O3 mechanism, Atmos. Chem. Phys., 19, 14535–14558, https://doi.org/10.5194/acp-19-14535-2019, 2019