Source and Chemistry of Hydroxymethanesulfonate (HMS) in Fairbanks, Alaska

Abstract:

Fairbanks, Alaska is a subarctic city that often has high levels of fine particle pollution during the winter, resulting from trapping by strong atmospheric inversions and local emissions and chemistry under cold and dark conditions. Aerosol particle samples collected on filters in winters 2018-2019 and 2019-2020 confirm the existence of abundant hydroxymethanesulfonate (HMS) in these conditions. HMS is an adduct of dissolved SO₂ and formaldehyde (HCHO), and may undergo further chemistry to produce particulate sulfate. During January-March of 2020, we deployed an online Particle into Liquid Sampler coupled to Ion Chromatography (PILS-IC) for quantification of HMS and inorganic sulfate in particle phase and a Laser Induced Fluorescence (LIF) instrument for HCHO in gas phase, along with ancillary measurements. We find that HMS serves as an important sulfur reservoir in the particle phase under cold conditions (T < -30 °C), with concentrations comparable to that of inorganic sulfate. We also find that HMS is correlated with inorganic sulfate during pollution events. The formation mechanism of HMS and its possible fate are further investigated with a multi-phase chemical box (0D) model constrained by ambient measurements. These observations and modeling of HMS formation under cold and dark conditions should improve our understanding of the relationship between secondary sulfur particulate species (HMS and sulfate) and precursor emissions (SO₂ and HCHO), providing the basis for improved regulations aimed at reducing these pollution events.