Effects of a Changing Climate on Primary and Secondary Organic Aerosols in the Arctic

In the Arctic, organic aerosols (OA) represent 10-40% of particulate mass; however, there is little understanding of their sources and composition due to limited measurements and under-constrained modeling. Improving the understanding of Arctic OA is essential to better represent aerosol direct and indirect radiative effects, which can contribute to radiative forcing and affect local climate. There are two types of OA: primary organic aerosol (POA), which is emitted directly from an anthropogenic source, and secondary organic aerosol (SOA), which is produced through complex chemical transformations of organic precursor species, such as volatile organic compounds. The sensitivity of SOA formation to environmental conditions (e.g., temperature and relative humidity) is poorly understood. Here, we investigate how climate change may impact SOA formation and composition for present-day, year 2050, and year 2100 conditions in polar regions. First, SOA and POA concentrations predicted by the Community Earth System Model (CESM) were compared to in-situ seasonal observations at eight Arctic stations. We found a general underprediction of SOA and a slight overprediction of POA by CESM, suggesting missing chemistry within the model. Future projections of SOA were analyzed and found to increase in the future, most likely due to decreasing NOx emissions and increasing biogenic emissions. Next, with the Generator of Explicit Chemistry and Kinetics Atmosphere (GECKO-A), we performed simulations for a temperature range of -33 to 25 ℃ for three precursors: toluene, dodecane, and a-pinene. These idealized simulations showed that decreasing temperature led to a change in SOA composition and increased SOA production rates, especially for low-NOx scenarios. Additionally, we simulate SOA formation and chemical processes at the eight station locations in the Arctic and along a lagrangian path to analyze the sources of Arctic OA, initialized with atmospheric conditions, emissions, and chemistry output from CESM for present-day and future conditions. Ultimately, we assess the impact of climate change on Arctic OA through full chemistry simulations, both idealized and realistic.