Enhancing anthropogenic NMVOC emission speciation for European air quality modelling.

Non-Methane Volatile Organic Compounds (NMVOCs) impact health and air quality, contributing to ozone and secondary organic aerosols (SOA). With stricter pollutant limits and a growing emphasis on modelling under the new European Ambient Air Quality Directive, improving NMVOC representation - particularly in terms of speciation - is essential. Current state-of-the-art European inventories rely on outdated data, potentially limiting accuracy. This study assesses for the first time the CAMS-REGv7.1 NMVOC emission inventory across Europe and evaluates the impact of replacing its default speciation with a more recent alternative using the MONARCH chemical transport model, comparing results with benzene, toluene and xylene observations for 2019. The impact of changing the speciation on modelled O is also quantified. The updated speciation shows significant changes in emissions across NMVOC species, with all species showing changes greater than ±15 %, significantly affecting their spatial distribution and sector contributions. Air quality modelling results show notable improvements for benzene (average NMB from -46.1 % to -27.7 %), primarily driven by a better split of residential wood combustion NMVOC proposed in this work. For toluene and xylenes, major overestimations previously observed in capital cities are largely reduced by improving the characterisation of solvent activities with the new speciation profiles. However, some areas showed degraded performance likely due to the over-allocation of industrial emissions in urban areas, limiting the assessment of speciation changes and worsening the overall underestimation. Despite significant changes in the split of NMVOCs, the proposed changes show minimal impact on modelled O levels, aside from localised spatial and temporal variability. The largest daily variations in MDA8 were -14 μg/m in March and +8 μg/m in May. The effects are smaller during summer, possibly due to an increasing role from biogenic emissions. Additional measurements of NMVOC species, along with more detailed model mechanisms, are needed to extend the evaluation.