Dimethyl sulfide oxidation in the equatorial Pacific: Comparison of model simulations with field observations for DMS, SO2, H2SO4(g), MSA(g), MS and NSS

Abstract. The response of marine low cloud systems to changes in aerosol concentration represents one of the largest uncertainties in climate simulations. Major contributions to this uncertainty are derived from poor understanding of aerosol under natural conditions and the perturbation by anthropogenic emissions. The eastern North Atlantic (ENA) is a region of persistent but diverse marine boundary layer (MBL) clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In this study, we examine MBL aerosol properties, trace gas mixing ratios, and meteorological parameters measured at the Atmospheric Radiation Measurement Climate Research Facility's ENA site on Graciosa Island, Azores, Portugal, during a 3-year period from 2015 to 2017. Measurements impacted by local pollution on Graciosa Island and during occasional intense biomass burning and dust events are excluded from this study. Submicron aerosol size distribution typically consists of three modes: Aitken (At, diameter Dp<∼100 nm), accumulation (Ac, Dp within ∼100 to ∼300 nm), and larger accumulation (LA, Dp>∼300 nm) modes, with average number concentrations (denoted as NAt, NAc, and NLA below) of 330, 114, and 14 cm−3, respectively. NAt, NAc, and NLA show contrasting seasonal variations, suggesting different sources and removal processes. NLA is dominated by sea spray aerosol (SSA) and is higher in winter and lower in summer. This is due to the seasonal variations of SSA production, in-cloud coalescence scavenging, and dilution by entrained free troposphere (FT) air. In comparison, SSA typically contributes a relatively minor fraction to NAt (10 %) and NAc (21 %) on an annual basis. In addition to SSA, sources of Ac-mode particles include entrainment of FT aerosols and condensation growth of Aitken-mode particles inside the MBL, while in-cloud coalescence scavenging is the major sink of NAc. The observed seasonal variation of NAc, being higher in summer and lower in winter, generally agrees with the steady-state concentration estimated from major sources and sinks. NAt is mainly controlled by entrainment of FT aerosol, coagulation loss, and growth of Aitken-mode particles into the Ac-mode size range. Our calculation suggests that besides the direct contribution from entrained FT Ac-mode particles, growth of entrained FT Aitken-mode particles in the MBL also represent a substantial source of cloud condensation nuclei (CCN), with the highest contribution potentially reaching 60 % during summer. The growth of Aitken-mode particles to CCN size is an expected result of the condensation of sulfuric acid, a product from dimethyl sulfide oxidation, suggesting that ocean ecosystems may have a substantial influence on MBL CCN populations in the ENA.

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Dimethyl sulfide in the Equatorial Pacific Ocean: A natural source of sulfur to the atmosphere

Geophysical Research Letters ◽

10.1029/gl010i010p00949 ◽

1983 ◽

Vol 10 (10) ◽

pp. 949-952 ◽

Cited By ~ 97

Author(s):

Joel D. Cline ◽

Timothy S. Bates

Keyword(s):

Pacific Ocean ◽

Dimethyl Sulfide ◽

Equatorial Pacific ◽

Natural Source ◽

Equatorial Pacific Ocean

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Missing SO<sub>2</sub> oxidant in the coastal atmosphere? – observations from high-resolution measurements of OH and atmospheric sulfur compounds

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-12209-2014 ◽

2014 ◽

Vol 14 (22) ◽

pp. 12209-12223 ◽

Cited By ~ 23

Author(s):

H. Berresheim ◽

M. Adam ◽

C. Monahan ◽

C. O'Dowd ◽

J. M. C. Plane ◽

...

Keyword(s):

Dimethyl Sulfide ◽

Sulfide Oxidation ◽

Research Station ◽

Ionization Mass ◽

Photochemical Degradation ◽

Background Signal ◽

So2 Oxidation ◽

Inlet System ◽

Criegee Intermediates ◽

Accommodation Coefficients

Abstract. Diurnal and seasonal variations of gaseous sulfuric acid (H2SO4) and methane sulfonic acid (MSA) were measured in NE Atlantic air at the Mace Head atmospheric research station during the years 2010 and 2011. The measurements utilized selected-ion chemical ionization mass spectrometry (SI/CIMS) with a detection limit for both compounds of 4.3 × 104 cm−3 at 5 min signal integration. The H2SO4 and MSA gas-phase concentrations were analyzed in conjunction with the condensational sink for both compounds derived from 3 nm to 10 μm (aerodynamic diameter) aerosol size distributions. Accommodation coefficients of 1.0 for H2SO4 and 0.12 for MSA were assumed, leading to estimated atmospheric lifetimes on the order of 7 and 25 min, respectively. With the SI/CIMS instrument in OH measurement mode alternating between OH signal and background (non-OH) signal, evidence was obtained for the presence of one or more unknown oxidants of SO2 in addition to OH. Depending on the nature of the oxidant(s), its ambient concentration may be enhanced in the CIMS inlet system by additional production. The apparent unknown SO2 oxidant was additionally confirmed by direct measurements of SO2 in conjunction with calculated H2SO4 concentrations. The calculated H2SO4 concentrations were consistently lower than the measured concentrations by a factor of 4.7 ± 2.4 when considering the oxidation of SO2 by OH as the only source of H2SO4. Both the OH and the background signal were also observed to increase significantly during daytime aerosol nucleation events, independent of the ozone photolysis frequency, J(O1D), and were followed by peaks in both H2SO4 and MSA concentrations. This suggests a strong relation between the unknown oxidant(s), OH chemistry, and the atmospheric photolysis and photooxidation of biogenic iodine compounds. As to the identity of the atmospheric SO2 oxidant(s), we have been able to exclude ClO, BrO, IO, and OIO as possible candidates based on {ab initio} calculations. Nevertheless, IO could contribute significantly to the observed CIMS background signal. A detailed analysis of this CIMS background signal in context with recently published kinetic data currently suggests that Criegee intermediates (CIs) produced from ozonolysis of alkenes play no significant role for SO2 oxidation in the marine atmosphere at Mace Head. On the other hand, SO2 oxidation by small CIs such as CH2OO produced photolytically or possibly in the photochemical degradation of methane is consistent with our observations. In addition, H2SO4 formation from dimethyl sulfide oxidation via SO3 as an intermediate instead of SO2 also appears to be a viable explanation. Both pathways need to be further explored.

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Boundary layer and free-tropospheric dimethyl sulfide in the Arctic spring and summer

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-8757-2017 ◽

2017 ◽

Vol 17 (14) ◽

pp. 8757-8770 ◽

Cited By ~ 3

Author(s):

Roghayeh Ghahremaninezhad ◽

Ann-Lise Norman ◽

Betty Croft ◽

Randall V. Martin ◽

Jeffrey R. Pierce ◽

...

Keyword(s):

Dimethyl Sulfide ◽

Transport Model ◽

Dispersion Model ◽

Open Water ◽

Particle Dispersion ◽

The Arctic ◽

Chemical Transport Model ◽

Model Simulations ◽

Baffin Bay ◽

Mixing Ratios

Abstract. Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada, in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut, and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign mean of 116 ± 8 pptv) compared to July 2014 (campaign mean of 20 ± 6 pptv). During July 2014, the largest mixing ratios were found near the surface over the ice edge and open water. DMS(g) mixing ratios decreased with altitude up to about 3 km. During April 2015, profiles of DMS(g) were more uniform with height and some profiles showed an increase with altitude. DMS reached as high as 100 pptv near 2500 m. Relative to the observation averages, GEOS-Chem (www.geos-chem.org) chemical transport model simulations were higher during July and lower during April. Based on the simulations, more than 90 % of the July DMS(g) below 2 km and more than 90 % of the April DMS(g) originated from Arctic seawater (north of 66° N). During April, 60 % of the DMS(g), between 500 and 3000 m originated from Arctic seawater. During July 2014, FLEXPART (FLEXible PARTicle dispersion model) simulations locate the sampled air mass over Baffin Bay and the Canadian Arctic Archipelago 4 days back from the observations. During April 2015, the locations of the air masses 4 days back from sampling were varied: Baffin Bay/Canadian Archipelago, the Arctic Ocean, Greenland and the Pacific Ocean. Our results highlight the role of open water below the flight as the source of DMS(g) during July 2014 and the influence of long-range transport (LRT) of DMS(g) from further afield in the Arctic above 2500 m during April 2015.

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