Characterization of humic-like substances in Arctic aerosols

Humic‐like substances (HULIS) are a complex group of relatively high molecular weight organic compounds which contribute considerably to the mass of organic carbon (OC) and influence the light‐absorbing properties of aerosols. In this work, HULIS were investigated for the first time in the high‐Arctic atmosphere, focusing on the chemical characterization and mass contribution of HULIS to the total suspended particle (TSP) mass using weekly aerosol samples collected at Station Nord, northeast Greenland every fourth week during 2010. Average HULIS‐C concentration was 11 ng C m−3 during the darker months (November–April) and 4 ng C m−3 during the other months (May–October) with an annual mass concentration of 0.02 ± 0.01 µg m−3. HULIS‐C contributed to 3–16% of water‐soluble organic carbon (WSOC), whereas HULIS accounted for 0.7–4.1% of TSP mass, with TSP typically below 1.0 µg m−3. Concentrations of OC, WSOC, HULIS, selected HULIS functional groups (carboxylic acids, aromatic carboxylic acids, and organosulfates) and levoglucosan overlapped with the typical Arctic haze pattern with elevated concentrations during winter to early spring. The aromatic carboxylic acid portion accounted for a larger share of total carboxylic acid of HULIS during the darker months (7%) compared to the brighter months (3%). The more abundant aromatic carboxylic acid functional groups and the moderate correlation between HULIS and levoglucosan concentrations during the darker months both indicate that biomass burning aerosols and thereby emissions of aromatic compounds could contribute to HULIS in the Arctic, especially during late winter. During the brighter months, relatively higher average molecular weight of HULIS was observed.