Global Importance of Hydroxymethanesulfonate in Ambient Particulate Matter: Implications for Air Quality

Abstract

Sulfur compounds are an important constituent of particulate matter, with impacts on climate and public health. While most sulfur observed in particulate matter has been assumed to be sulfate, laboratory experiments reveal that hydroxymethanesulfonate (HMS), an adduct formed by aqueous phase chemical reaction of dissolved HCHO and SO 2 , may be easily misinterpreted in measurements as sulfate. Here we present observational and modeling evidence for a ubiquitous global presence of HMS. We find that filter samples collected in Shijiazhuang, China, and examined with ion chromatography within 9 days show as much as 7.6 μg m −3 of HMS, while samples from Singapore examined 9-18 months after collection reveal~0.6 μg m −3 of HMS. The Shijiazhuang samples show only minor traces of HMS 4 months later, suggesting that HMS had decomposed over time during sample storage. In contrast, the Singapore samples do not clearly show a decline in HMS concentration over 2 months of monitoring. Measurements from over 150 sites, primarily derived from the IMPROVE network across the United States, suggest the ubiquitous presence of HMS in at least trace amounts as much as 60 days after collection. The degree of possible HMS decomposition in the IMPROVE observations is unknown. Using the GEOS-Chem chemical transport model, we estimate that HMS may account for 10% of global particulate sulfur in continental surface air and over 25% in many polluted regions. Our results suggest that reducing emissions of HCHO and other volatile organic compounds may have a co-benefit of decreasing particulate sulfur.

Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants

“…Recent work also identified the potential of IO x ion chemistry to lead to measurement interferences (Dörich et al, 2021) and of the detection of acid gases, which could impact the measured HOCl : HCl ratio. Furthermore, rapid interconversion of halogen species on inlet walls has been reported that could also impact the measured HOCl : HCl ratio (Neuman et al, 2010).…”

Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds

“…3 or SO −2 3 can react with a variety of aldehydes to form hydroxyalkylsulfonates (Olson and Hoffmann, 1989). Of particular interest has been the S(IV) reaction with HCHO to produce hydroxymethanesulfonate (HMS; HOCH 2 SO − 3 ; Munger et al, 1986). The formation of HMS is strongly dependent on drop acidity, which increases rapidly at higher pH values due to the increased partitioning of S(IV) to HSO − 3 and SO 2− 3 (Rao and Collett, 1995).…”

Further improvement of wet process treatments in GEOS-Chem v12.6.0: impact on global distributions of aerosols and aerosol precursors

“…10.55 298.15 T −1 , K 1 = 1.3 × 10 −2 e 6.75 298.15 T −1 , K 2 = 6.31 × 10 −8 e 5.05 298.15 T −1 298.15 T −1 , K 3 = 2.2 × 10 −12 e 12.52 298.15 T −1 (Alexander et al, 2012). This iterative calculation is updated to use Newton's method in order to arrive at a consistent result (Moch et al, 2020). To implement Newton's method, the equilibrium expressions for the concentrations of each soluble semivolatile ion (SSVI) in terms of H + and the derivatives for these equilibrium expressions are each solved explicitly so that Newton's method equation is in the form of…”

“…To reflect the impact of soluble nonvolatile cations on cloud water pH, we assume that total G. Luo et al: Improved wet processes in GEOS-Chem and global validations amount of soluble nonvolatile cations associated with aerosol thermodynamics (SNVC) is 25 % of sulfate. We also consider the contribution of calcium and magnesium based on simulated dust mass in GC12, assuming that 3 % of dust mass is soluble calcium and 0.6 % is soluble magnesium (Farlie et al, 2010;Moch et al, 2020), to SNVIs:…”