Global modeling of heterogeneous hydroxymethanesulfonate chemistry

Abstract

Abstract. Hydroxymethanesulfonate (HMS) has recently been identified as an abundant organosulfur compound in aerosols during winter haze episodes in northern China. It has also been detected in other regions, although the concentrations are low. Because of the sparse field measurements, the global significance of HMS and its spatial and seasonal patterns remain unclear. Here, we implement HMS chemistry into the GEOS-Chem chemical transport model and conduct multiple global simulations. The developed model accounts for cloud entrainment and gas–aqueous mass transfer within the rate expressions for heterogeneous sulfur chemistry. Our simulations can generally reproduce the available HMS observations, and show that East Asia has the highest HMS concentration, followed by Europe and North America. The simulated HMS shows a seasonal pattern with higher values in the colder period. Photochemical oxidizing capacity affects the competition of formaldehyde with oxidants (such as ozone and hydrogen peroxide) for sulfur dioxide and is a key factor influencing the seasonality of HMS. The highest average HMS concentration (1–3 μg m−3) and HMS/sulfate molar ratio (0.1–0.2) are found in northern China winter. The simulations suggest that aqueous clouds act as the major medium for HMS chemistry while aerosol liquid water may play a role if its rate constant for HMS formation is greatly enhanced compared to cloud water.

Influence of atmospheric in-cloud aqueous-phase chemistry on the global simulation of SO<sub>2</sub> in CESM2

“…Recent studies show that hydroxymethanesulfonate (HMS), formed by aqueous-phase reactions of dissolved HCHO and SO 2 , is an abundant organosulfur compound in aerosols during winter haze episodes and suggest that aqueous clouds act as the major medium for HMS chemistry (Moch et al, 2020;Song et al, 2021). Therefore, it is necessary to further investigate the influence of this organic chemistry on the incloud aqueous-phase chemistry system in CESM2.…”

Emission factors and evolution of SO2measured from biomass burning in wildfires and agricultural fires

“…Recent studies have suggested HCHO to be an important aqueous-phase oxidant at reduced temperatures (Moch et al, 2018;Song et al, 2021). However, HCHO is also an indicator of smoke age, with mixing ratios typically being largest nearest to the fire source (Liao et al, 2021).…”

“…However, the chemistry is likely to be different as a result of differing emissions. In addition, it has been suggested that unaccounted for hydroxymethanesulfonate (HMS) formation may explain the discrepancy between measured and modeled sulfate values (Dovrou et al, 2019;Song et al, 2021).…”