Investigating the drivers of future changes in Arctic aerosols in UKESM1 using a Lagrangian air-mass trajectory framework

Aerosols are well-known climate forcers, yet their climatic impact on the Earth’s radiative budget remains uncertain. One of the reasons for this is poor representation of the aerosol-cloud interaction (ACI) process in the current Global Climate models (GCMs). Aerosol number size distributions in the atmosphere influence key ACI-relevant aerosol and cloud properties and, therefore, need to be accurately represented in GCMs. Understanding aerosol sources and sinks in pristine polar regions is crucial for improving climate projections, as several studies highlight the poor performance of GCMs in these areas. Moreover, it offers the advantage of understanding the impact of future changes in transport patterns on aerosol-climate feedback in sensitive background regions. To this end, improved representation of the regional distribution of aerosol emissions, and their temporal variations in climate models for near-term projections is a crucial gap that needs urgent attention. As the European Union (EU) aims to be climate-neutral by 2050, this study seeks to advance our understanding of aerosol life cycle processes in response to future regional emission changes.

We capitalise on a recently developed framework from the AeroCom Phase III GCM Trajectory (GCMTraj ) experiment, which leverages GCM meteorological fields to calculate the air-mass trajectories (Kim et al., 2020). Our work utilises the free-running and nudged UKESM1-0-LL versions from Regional Aerosol Model Intercomparison Project (RAMIP) simulations to calculate the trajectories and perform a spatio-temporal collocation of aerosol diagnostics. Here, we explore the various shared socioeconomic pathways (SSP370 and SSP370-126aer) from RAMIP to compare the impacts of global warming and aerosol reductions on future aerosol trends. This is the first time the free-running simulations from RAMIP have been used to calculate future air-mass trajectories. Using these trajectories we analyse the changes in source-receptor trends resulting from significant regional emission reductions in the post-fossil Arctic aerosol regime (2050) at Mt. Zeppelin.

We find continental air-mass transport from the northwest, Nordic and Siberian regions, towards the receptor site, Mt. Zeppelin and a strong seasonal variation in the transport patterns between 2010-2014 and 2046-2050. These results contrast with trajectories derived from ERA-Interim, ERA5 reanalysis and UKESM1 (nudged version), which reveal dominant air mass transport from the south-west, Eurasia and the northern Atlantic Ocean between 2010-2014. The results demonstrating seasonal characteristics of aerosol sources and sinks owing to changes in future circulation and emission patterns will be presented. This work will help improve knowledge of ACI evolution in response to changes in regional emission trends in the post-fossil remote aerosol regime.