Modelling taxonomic biodiversity driven effects on regional air quality using the new chemical mechanism URMELL

Air quality is a globally pressing issue as it poses a major threat for human health and ecosystems. Non-methane volatile organic compounds (NMVOCs) are highly reactive substances and known for their impact on the HO_x (OH + HO₂) and NO_x (NO + NO₂) budget. Important air pollutants such as ozone and particulate matter (PM) in terms of secondary organic aerosols (SOA) result from the chemical oxidation of NMVOCs. NMVOCs comprise a variety of anthropogenic and biogenic compounds with highly complex and interwoven interrelations. Therefore, it is key to capture these interdependencies for any air quality model assessment. Here we emphasize the importance of considering taxonomic biodiversity for regional air quality modeling by integrating the most common European tree species (116 tree classes) into the model framework COSMO-MUSCAT. This has major impacts on modeled biogenic NMVOC emissions and the tropospheric oxidizing capacity which is also impacting the chemical degradation of anthropogenic VOCs. To entangle these complex interdependencies the new chemical mechanism URMELL (short for: Urban and Remote cheMistry modELLing) was developed. URMELL comprises an extended chemical treatment of major anthropogenic (e.g. aromatics) and biogenic (e.g. isoprene) NMVOCs. By maintaining reaction products with multiple functional groups as possible SOA precursors, URMELL enables a direct and explicit SOA approach and considers HO_x/NO_x regime shifts creating a multitude of individual SOA species. URMELL simulates higher contributions of non- and lower volatile isoprene and aromatic products. Unexpected high concentrations of non-volatile aromatic SOA products are reached in remote spruce forests, away from the emission sources.