Air pollution transported from mid-latitudes influences the Arctic during wintertime, leading to the formation of Arctic Haze. Local emissions, such as combustion for heating in cold winter conditions, also contribute to wintertime air pollution. However, the formation of secondary aerosol particles in cold/dark wintertime Arctic conditions, is poorly understood. In this study, which contributes to the Air Pollution in the Arctic: Climate, Environment and Societies - Alaskan Layered Pollution and Arctic Chemical Analysis (PACES-ALPACA) initiative, the Weather Research Forecasting Model with chemistry (WRF- Chem) is used to investigate wintertime pollution over Alaska focusing on Prudhoe Bay and the Fairbanks region, respectively. Fairbanks is the most polluted city in the United States during wintertime, due to high local emissions and the occurrence of strong surface temperature inversions trapping pollutants near the surface. On the other hand, the Prudhoe Bay oilfields contribute to wintertime air pollution in northern Alaska. In a first study, the sensitivity of simulated aerosols to local anthropogenic emissions is investigated over northern Alaska and evaluated against observations at Utqiaġvik, collected during a campaign in Jan-Feb 2014. FLEXible PARTicle dispersion model coupled with WRF, is also used to identify the pollutant origins in air masses in the boundary layer, which are influencing Utqiaġvik during periods with elevated aerosols. The contribution of locally produced anthropogenic and natural aerosols relative to remote pollutants is also examined. In a second study, focusing on winter 2019 (ALPACA pre-campaign) over Fairbanks, large- scale synoptic conditions and remote anthropogenic sources affecting background aerosols are estimated. The sensitivity of secondary aerosol formation to meteorological factors, such as relative humidity, boundary layer stability are examined. Discrepancies in modelled secondary aerosols compared to available data are investigated (e.g. missing dark formation mechanisms, removal processes, emissions). The role of local/regional dynamical processes influencing aerosols under different meteorological conditions observed during the field campaign, such as a cold stable episode or a period with potential mixing of air masses from aloft, are also investigated.