Rapid cloud removal of dimethyl sulfide oxidation products limits SO ₂ and cloud condensation nuclei production in the marine atmosphere

Abstract

Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The oxidation of DMS leads to the formation and growth of cloud condensation nuclei (CCN) with consequent effects on Earth’s radiation balance and climate. The quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of existing aerosol particles and clouds. In the unpolluted marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory toward sulfur dioxide (SO2) and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that the irreversible loss of HPMTF to clouds in the marine boundary layer determines the HPMTF lifetime (τHPMTF < 2 h) and terminates DMS oxidation to SO2. When accounting for HPMTF cloud loss in a global chemical transport model, we show that SO2 production from DMS is reduced by 35% globally and near-surface (0 to 3 km) SO2 concentrations over the ocean are lowered by 24%. This large, previously unconsidered loss process for volatile sulfur accelerates the timescale for the conversion of DMS to sulfate while limiting new particle formation in the marine atmosphere and changing the dynamics of aerosol growth. This loss process potentially reduces the spatial scale over which DMS emissions contribute to aerosol production and growth and weakens the link between DMS emission and marine CCN production with subsequent implications for cloud formation, radiative forcing, and climate.

Efficient Production of Carbonyl Sulfide in the Low‐NOx Oxidation of Dimethyl Sulfide

“…As discussed in G. A. Novak et al. (2021), we find that multiphase chemistry has an irreversible and significant impact on [HPMTF] suppressing OCS production. The addition of HPMTF multiphase chemistry reduces P OCS from 680.1 to 52.9 Gg S yr −1 with the largest differences found in regions of high cloud cover at high latitudes (Eastman et al., 2011; King et al., 2013; Figure 3a).…”

“…This approach is compared with the existing, fixed-yield model where 𝐴𝐴 𝐴𝐴OCS = 𝑌𝑌OCS × 𝐿𝐿DMS , 𝐴𝐴 𝐴𝐴OCS = 0.7% and 𝐴𝐴 𝐴𝐴DMS is the loss rate of DMS to reaction with OH or 𝐴𝐴 𝐴𝐴DMS+OH[OH][DMS] . We used the GEOS-Chem global chemical transport model with an expanded DMS oxidation mechanism and model updates to halogen chemistry and cloud processing (Holmes et al, 2019;G. A. Novak et al, 2021;Veres al., 2020;Wang et al, 2019Wang et al, , 2021version 12.9.2, www.geos-chem.org, see in Supporting Information S1 for more details).…”

“…Recent isotopic and inverse modeling studies indicate that the marine environment is the dominant source region for OCS and that there is either an over-estimation of the terrestrial OCS sink or an unaccounted-for OCS source that seems to be centered in the tropical oceans based on atmospheric inversion studies (Berry et al, 2013;Davidson et al, 2021;Ma et al, 2021). In response to recent suggestions that the production of OCS from the OH-initiated oxidation of DMS may be a significant source of uncertainty in the OCS budget (Davidson et al, 2021;Ma et al, 2021) and new discoveries of the chemical mechanism of DMS oxidation (Berndt et al, 2019;G. A. Novak et al, 2021;Veres et al, 2020;Wu et al, 2015), we revisit here the chemical mechanism for OCS production in the oxidation of DMS.…”

Butene Emissions From Coastal Ecosystems May Contribute to New Particle Formation

“…Concerning aerosol production, organic photochemistry is not considered at all in climate models as it is computationally expensive. Efforts are being made to include the chemistry of DMS from marine biogenic emissions as it has been recognised as important for the Earth's climate being an efficient aerosol and cloud droplet producer (Fung et al., 2022; Grandey & Wang, 2015; Mayer et al., 2020; Novak et al., 2021). We showed that butenes may also contribute to marine NPF, deserving a place in climate models that currently account for “unknown organic emissions” with a scaling factor applied to DMS emissions (Bodas‐Salcedo et al., 2019; Mulcahy et al., 2018).…”

Technical note: Entrainment-limited kinetics of bimolecular reactions in clouds

“…The original paper applied entrainment-limited uptake to first-order loss of nitrogen oxide compounds (NO 2 , NO 3 , N 2 O 5 ) and showed that clouds are a globally significant sink for these gases (Holmes et al, 2019). The method has since been applied to nitrogen oxide isotopes (Alexander et al, 2020), nitrate in urban haze (Chan et al, 2021), dimethyl sulfide oxidation products (Novak et al, 2021;Jernigan et al, 2022), mercury (Shah et al, 2021), and reactive halogens (Wang et al, 2021), all of which also involved first-order loss reactions in clouds. This note derives entrainment-limited reaction kinetics for bimolecular reactions with second-order kinetics so that the entrainment-limited method can be applied to a wider range of chemical systems that are important in the atmosphere.…”