Simulating Air Quality in the United Kingdom with the Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA)

Air pollution in the United Kingdom (UK) is an important public health concern, with an estimated 40,000 premature deaths annually attributed to it. Although previous studies have used surface observations to assess the potential effects of pollutants like PM2.5 and NOx in the UK, these networks offer limited spatial and temporal coverage and are unable to simulate the effects of global or local environmental changes on UK air quality. Consequently, atmospheric chemistry models play a vital role in understanding atmospheric processes of gases and aerosols as well as the interactions between atmospheric chemistry, weather, and climate. Currently, models with distinct infrastructures are used independently (e.g., EMEP4UK coupled with WRF) to address varying spatial scales in atmospheric chemistry research in the UK, which may potentially introduce inconsistencies in simulation results due to different mechanisms or physical parameters of the models. The Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA) enables the representation of large-scale atmospheric phenomena, while still resolving chemistry at emission-relevant and exposure-relevant scales in a consistent way. In this study, we employed MUSICA version 0 (MUSICAv0), a configuration of the Community Earth System Model (CESM) with regional refinement (RR), to investigate air quality simulation in the UK. To better represent the spatial distribution of simulated air pollutant concentrations over the UK, we have developed a regional refinement grid (ne30×16 [~7km]) in comparison to the original grid (ne30 [~111km]). This refinement is crucial as grid resolution can impact air pollutant concentrations in the boundary layer by an order of magnitude. To validate the simulation results, we used in situ air quality observational data from the Automatic Urban and Rural Network (AURN), which comprises 150 active sites across the UK and serves as the primary network for compliance reporting under the Ambient Air Quality Directives. This study facilitates effective analysis of the temporal and spatial variations in surface air pollutant concentrations across the UK and provides a foundation for future scenario simulations, such as regional and global impacts of achieving net-zero carbon emissions.