Complementary aerosol mass spectrometry elucidates sources of wintertime sub-micron particle pollution in Fairbanks, Alaska, during ALPACA 2022 

Abstract. Fairbanks, Alaska, is a subarctic city that frequently suffers from non-attainment of national air quality standards in the wintertime due to the coincidence of weak atmospheric dispersion and increased local emissions. However, significant uncertainties exist about aerosol sources, formation, and chemical processes during cold winter periods. We aim to determine the composition, size, and concentrations of atmospheric sub-micron non-refractory particulate matter (NR-PM­₁) and quantify their sources in the urban centre of Fairbanks. As part of the Alaskan Layered Pollution and Chemical Analysis (ALPACA) campaign, we deployed a Chemical Analysis of Aerosol Online (CHARON) inlet coupled with a proton transfer reaction – time of flight mass spectrometer (PTR-ToF MS) and an Aerodyne high-resolution aerosol mass spectrometer (AMS) to measure organic aerosol (OA) and NR-PM₁, respectively. We used positive matrix factorisation (PMF) for source identification. PTR_CHARON factorisation delineated four residential heating sources, including wood and oil combustion, that contribute 47 ± 20 % and 16 ± 9 % of OA_CHARON, on average, respectively. In contrast, only a single biomass burning-related factor was identified by AMS for both OA and NR-PM₁, but it provided information on two additional factors that were rich in sulphur and nitrate. These results demonstrate that PTR_CHARON can generate robust quantitative information with enhanced resolution of organic aerosol sources. When combined with suitable complementary instruments like the AMS, such evidence-based insights into the sources of sub-micron aerosol pollution can assist environmental regulators and citizen efforts for the improvement in air quality in Fairbanks and in the wider Arctic winter.