Photooxidation Of Dimethylsulfide Research Articles

Distribution Characteristics of Dimethylated Sulfur Compounds and Turnover of Dimethylsulfide in the Northern South China Sea During Summer

AbstractSpatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethyl sulfoxide (DMSO) in the northern South China Sea were determined in the summer of 2015. The mean concentrations of DMS, particulate DMSP (DMSPp), dissolved DMSP (DMSPd), dissolved DMSO (DMSOd), and particulate DMSO (DMSOp) in the surface seawater were 2.8 ± 1.0, 6.8 ± 1.5, 14.0 ± 3.1, 12.2 ± 3.2, and 9.2 ± 2.6 nmol L−1, respectively. The contributions of three principal removal pathways of DMS were investigated. The average biological production and consumption rates of DMS in the surface seawater were 6.15 ± 1.12 and 4.63 ± 1.32 nmol L−1 day−1. Deck incubation experiments showed that the photooxidation rates of DMS for different radiation bands followed the order: KUVB > KUVA > Kvisible light. The DMS photooxidation rates were higher in the coastal waters than in the open ocean, which might be associated with the higher concentrations of dissolved organic matter of terrigenous input. The sea‐to‐air fluxes of DMS ranged from 1.6 to 50.3 μmol m−2 day−1 with an average value of 15.6 ± 11.6 μmol m−2 day−1. Based on the respective turnover times of DMS, the contributions of biological consumption, photooxidation, and sea‐to‐air exchange to the sink of DMS were 32.6 ± 11.0%, 23.2 ± 8.9%, and 44.1 ± 19.2%, respectively, suggesting that the three removal pathways were all critical to the migration and transformation of DMS in the surface seawater during summer.

Distribution, Occurrence, and Fate of Biogenic Dimethylated Sulfur Compounds in the Yellow Sea and Bohai Sea During Spring

AbstractThe spatial distributions of biogenic dimethylated sulfur compounds (BDSCs), including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide, were determined in the Yellow Sea and Bohai Sea during a survey in April–May 2014 and the occurrence and fate of BDSCs in the surface seawater were investigated. The concentrations of DMS and DMSP were significantly correlated with the stocks of chlorophyll a and a decreasing trend was observed from the inshore to the offshore areas. In situ incubation experiments indicated that more than half of the degraded dissolved DMSP (DMSPd) was transformed into DMS. Irradiation experiments showed that the photooxidation of DMS under ultraviolet B, ultraviolet A, and visible light accounted for 23.9%, 71.8%, and 4.3% of the total photooxidation of DMS, respectively. The sea‐to‐air fluxes of DMS ranged from 0.24 to 34.11 μmol m−2 day−1 with a mean of 8.84 μmol m−2 day−1. A comparison of the DMS production rate and main removal rates indicated that bioproduction cannot completely maintain the removal of DMS and might not be the only but the primary source of DMS in the surface seawater. Additionally, the average turnover times of microbial consumption, photooxidation, and sea‐to‐air exchange of DMS were 1.53, 1.16, and 4.28 day and the contributions of the three removal pathways were 40.0%, 41.2%, and 18.8% respectively; this indicated that microbial consumption and photooxidation played dominant roles in controlling the removal of DMS from the surface seawater.

Transparent Organosilica Photocatalysts Activated by Visible Light: Photophysical and Oxidative Properties at the Gas–Solid Interface

The photophysical properties of several photosensitizers (PSs) included or grafted in silica monoliths were compared to their properties in solution. The effects of the solid support on their steady-state and transient absorption spectra, on their quantum yields of singlet oxygen ((1)O2) production, and on their ability to photoinduce the oxidation of dimethylsulfide (DMS) were investigated. Two cyanoanthracene derivatives (9,14-dicyanobenzo[b]triphenylene, DBTP, and 9,10-dicyanoanthracene, DCA), as well as three phenothiazine dyes (methylene blue, MB(+), new methylene blue, NMB(+), methylene violet, MV), were encapsulated in silica, analyzed and compared to two reference PSs (perinaphthenone, PN and rose bengal, RB). A DBTP derivative (3-[N-(N″-triethoxysilylpropyl-N'-hexylurea)]carboxamido-9,14-dicyanobenzo[b]triphenylene, 3) was also prepared and grafted onto silica. Thanks to the transparency and the free-standing shape of the monoliths, the complete spectroscopic characterization of the supported PSs was carried out directly at the gas-solid interface. The influence of the silica network, the PS, and the adsorption/grafting link between the PS and silica was investigated. The effects of PS concentration, gaseous atmosphere, humidity, and hydrophobicity on the production of (1)O2 were analyzed. With all PSs, (1)O2 production was very efficient (quantum yields of (1)O2 production, relative to PN, between 0.6 and 1), and this species was the only one involved in the pollutant photooxidation. The influence of the matrix on the PSs' photophysics could be considered as negligible. In contrast, the matrix effect on DMS photooxidation was extremely important: the gas diffusion inside the porous structure, and thus, the photoactivity of the materials, strictly depended on silica's surface area and porosity. Our results highlight the suitability of these silica structures as inert supports for the study of the photosensitizing properties at the gas-solid interface. Moreover, thanks to the adsorption properties of the matrix, the synthesized materials can be used as microphotoreactor for the (1)O2-mediated oxidation of volatile pollutants.

Photooxidation of dimethylsulfide (DMS) in the Canadian Arctic

Abstract. Photolysis of dimethylsulfide (DMS), a secondary photochemical process mediated by chromophoric dissolved organic matter (CDOM), has previously been demonstrated to be an important loss term of DMS in the surface layer of warm seas and the Southern Ocean. The role of photolysis in regulating the DMS dynamics in northern polar seas remains, however, less clear. This study for the first time determined the apparent quantum yield (AQY) spectra of DMS photooxidation in Canadian Arctic seas covering Baffin Bay, the Mackenzie estuary and shelf, and the Canada Basin. The DMS AQY was fairly invariant at salinities < 25 but rose rapidly with further increasing salinity in an exponential manner. Salinity can therefore be used as a quantitative indicator of the DMS AQY. The DMS AQY in the ultraviolet (UV) wavelengths was linearly and positively correlated with the spectral slope coefficient (275–295 nm) of the CDOM absorption spectrum, suggesting that marine CDOM photosensitizes the degradation of DMS more efficiently than does terrestrial CDOM or that coastal waters contain higher concentrations of substrates (most likely dissolved organic matter and redox metals) that compete for DMS-oxidizing radical intermediates. High concentrations of nitrate (~ 12 μmol L−1) in deep water samples boosted DMS photooxidation by 70–80%, due likely to radical chemistry of nitrate photolysis. Coupled optical-photochemical modeling, based on the obtained DMS AQY spectra, shows that UV-A (320–400 nm) accounted for 60–75% of the DMS photolysis in the sunlit surface layer and that photochemistry degraded DMS on an e-folding time from 9 to 100 d (mean: 29 d). The photooxidation term on average accounted for 21% of the DMS gross loss rate and was comparable to the atmospheric DMS ventilation rate estimated for the same geographic regions. The methodology adopted here to study the relationship between CDOM quality/origin and DMS AQYs, if applicable to other ocean areas, may bring results of global significance for DMS cycling and might have implications for probing other CDOM-driven photochemical processes.

Chamber simulation of photooxidation of dimethyl sulfide and isoprene in the presence of NO<sub>x</sub>

Abstract. To improve the model prediction for the formation of H2SO4 and methanesulfonic acid (MSA), aerosol-phase reactions of gaseous dimethyl sulfide (DMS) oxidation products [e.g., dimethyl sulfoxide (DMSO)] in aerosol have been included in the DMS kinetic model with the recently reported gas-phase reactions and their rate constants. To determine the rate constants of aerosol-phase reactions of both DMSO and its major gaseous products [e.g., dimethyl sulfone (DMSO2) and methanesulfinic acid (MSIA)], DMSO was photooxidized in the presence of NOx using a 2 m3 Teflon film chamber. The rate constants tested in the DMSO kinetic mechanisms were then incorporated into the DMS photooxidation mechanism. The model simulation using the newly constructed DMS oxidation mechanims was compared to chamber data obtained from the phototoxiation of DMS in the presence of NOx. Within 120-min simulation, the predicted concentrations of MSA increase by 200–400% and those of H2SO4, by 50–200% due to aerosol-phase chemistry. This was well substantiated with experimental data. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the newly constructed DMS kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. With the high concentrations of DMS (250 ppb) and isoprene (560–2248 ppb), both the model simulation and experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.

Red-light-induced Photoreaction of DMS–O3 Complex in a Cryogenic Neon Matrix

Abstract Photoreaction and light absorption of dimethyl sulfide (DMS)–O3 complex isolated in a cryogenic neon matrix were investigated by FTIR and visible-light absorption spectroscopy. Although visible light does not induce photoreaction for either monomer, a photoreaction to produce dimethyl sulfoxide (DMSO) was observed to occur upon the red light (700–740 nm) irradiation. New electronic absorption bands peaking at 470 and 600 nm due to DMS–O3 complex appear in a visible spectral region, which are responsible for the photooxidation of DMS to DMSO.

Secondary organic aerosol formation from photooxidation of a mixture of dimethyl sulfide and isoprene

Abstract Secondary organic aerosol (SOA) created from the photooxidation of a mixture of isoprene and dimethyl sulfide (DMS) was studied at different NO x concentrations (40–220 ppb) and humidities (12%, 42% and 80%) using a Teflon film indoor chamber. To study the effect of isoprene on DMS products, the major DMS photooxidation products, such as sulfuric acid, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA), were quantified in both the presence and the absence of isoprene using a Particle-Into-Liquid-Sampler coupled with Ion Chromatography (PILS-IC). The resulting PILS-IC data showed that the DMS aerosol yield significantly decreased due to the photooxidation of isoprene. A 35.2% DMS aerosol yield reduction was observed due to 800 ppb isoprene in 185 ppb NO x and 140 ppb DMS. Among the aerosol-phase DMS oxidation products, MSA was the most sensitive to the presence of isoprene (e.g., 46% reduction). The DMS aerosol product analysis indicates that isoprene oxidation affects the pathways of MSA formation on the aerosol surface. Using a new approach that implements an Organic Carbon (OC) analyzer, the isoprene SOA yield ( Y iso ) in the DMS/isoprene/NO x system was also estimated. The OC data showed that Y iso increased significantly with DMS compared to the Y iso without DMS. For example, Y iso with 80 ppb NO x and 840 ppb isoprene was increased by 124.6% due to 100 ppb DMS at RH = 42%. Our study suggests that the heterogeneous reactions of isoprene oxidation products with the highly acidic products (e.g., MSA and sulfuric acid) from DMS photooxidation can considerably contribute to the Y iso increase.

Light‐stimulated production of dissolved DMSO by a particle‐associated process in the Ross Sea, Antarctica

Dimethylsulfoxide (DMSO) is an abundant form of methylated sulfur in marine systems and it is known to be produced from dimethylsulfide (DMS). Using radiolabeled 35S‐DMS and gas chromatography techniques, we quantified the dissolved DMSO (DMSOd) produced from photo‐ and biological oxidation of dissolved DMS and compared the DMSOd production from these pathways with the net change in DMSOd concentrations in unfiltered seawater samples. The net change in DMSOd in light‐exposed treatments exceeded DMSOd production from photo‐ plus biological oxidation of dissolved DMS. This indicated that DMSOd was produced by one or more light‐driven processes likely associated with particulate material. Results from in situ incubation arrays showed that the relative importance of DMSOd production processes was dependent on irradiation depth, with the unidentified particle‐associated process and dissolved DMS photooxidation the main DMSOd sources close to the surface (0–10 m) and biological oxidation of dissolved DMS the main process at depths at which the light level was low (>10 m). Deckboard and in situ incubations revealed that DMSOd production from the particle‐associated process was stimulated by ultraviolet radiation. Higher particle‐associated production of DMSOd in samples more prone to suffer light‐induced stress supports the hypothesis that this process was related to phytoplanktonic biosynthesis and release of DMSO because of oxidative stress. Our results suggest that particle‐associated DMSOd production is an important source of DMSOd in surface waters of the Ross Sea and also help to explain why DMSOd is periodically the main organosulfur compound detected in the upper water column.

Photooxidation of dimethylsulfide in the gas phase: A comparison between TiO2–silica and photosensitizer-silica based materials

The photooxidation of dimethylsulfide (DMS) in the gas phase was studied with two different materials, under identical conditions. The first material (TiO2-QZ) is based on titanium dioxide (TiO2) deposited on quartz bars by the sol–gel method. The second one (DCA-SG) is based on the well known photosensitizer, 9,10-dicyanoanthracene (DCA) encapsulated in a sol–gel silica network. In spite of non-optimized conditions, both materials allow the oxidation of DMS in air under irradiation. However, the oxidation products are strikingly different: dimethyldisulfide is the main product detected in the gas phase with TiO2-QZ due to a too short residence time to achieve complete mineralization. With DCA-SG no gaseous product is detected in the treated gaseous flow for more than 100h, due to the exclusive formation of polar dimethylsulfoxide and dimethylsulfone which are totally adsorbed on the highly polar silica gel. The efficiency of this latter reaction depends on the DMS concentration, gas flow and light intensity, but is not affected by the presence of small amounts of water. Singlet oxygen appears to be formed efficiently under these conditions. The saturation of DCA-SG by the oxidation products was demonstrated by several complementary methods, and some possible solutions to regenerate the material are proposed. The complementarities of both TiO2-QZ and DCA-SG could be used to achieve the oxidation of different classes of pollutants.

Modeling of dimethyl sulfide ocean mixing, biological production, and sea‐to‐air flux for high latitudes

To explore the extent to which ocean mixed‐layer dynamics influences dimethyl sulfide (DMS) sea‐to‐air flux at high latitudes, a model of DMS ocean mixing, biological production, and sea‐to‐air flux was developed. This biophysical one‐dimensional model is driven by meteorology. The model simulates DMS seawater concentrations and vertical distributions, and DMS sea‐to‐air flux for Prince William Sound and the Gulf of Alaska, from early March through December. Sensitivity analyses revealed that DMS sea‐to‐air flux is most affected by the rates of flagellate production, Zooplankton grazing, photooxidation, and microbial consumption of DMS. Model results show that under conditions of substantial vertical mixing, such as high wind stress or convective mixing, DMS sea‐to‐air flux increases significantly. At high latitudes these events may coincide with wind‐driven mixing or the overturning of surface seawater due to decreasing sea surface temperatures in the autumn. Parameterizations used to estimate emissions of such a highly variable gas as dimethyl sulfide need to include ocean mixed‐layer dynamics. The current model is limited by the small number of DMS loss and production rate measurements available. The measurements that do exist have large ranges and come almost exclusively from low and midlatitude regions, mostly during the summer months under calm conditions. Field measurements are needed from high‐latitude systems to refine this model, making it an effective tool for designing field campaigns, improving the accuracy of DMS sea‐to‐air flux estimations, and assessing the contribution of northern oceans to the atmospheric sulfur budget.

A direct method of calculating sensitivity coefficients of chemical kinetics

In this paper, a new direct method of calculating the first-order sensitivity coefficients using sparse matrix technology to chemical kinetics is presented. The Gear type procedure is used to integrate a model equation and its coupled auxiliary sensitivity coefficient equations. Because the Jacobian matrix of the model equation is the same as that of the sensitivity coefficient equation with respect to a parameter, it is only necessary to triangularize the matrix related to the Jacobian matrix of the model equation. The FORTRAN subroutines of the model equation, the sensitivity coefficient equations, and their Jacobian analytical expressions are generated automatically from chemical mechanism. This method greatly increases the efficiency of computation by taking advantage of the fact that the auxiliary equations for different sensitivity coefficients are linear and quite similar. Two sets of chemical reactions are used to illustrate this approach: oxidation of formaldehyde in the presence of carbon monoxide and photo-oxidation of dimethyl sulfide. The accuracy and computational efficiency of the new direct method is demonstrated by comparing the results from the new direct method and from the indirect method.

Observations of dimethyl sulfide over the western North Atlantic Ocean using an airborne tandem mass spectrometer

An atmospheric sampling tandem mass spectrometer has been evaluated for aircraft monitoring of dimethyl sulfide (DMS) and then used for DMS monitoring during portions of six flights over the western North Atlantic Ocean. Laboratory evaluations demonstrated that the mass spectrometer is highly selective for DMS, and responds linearly over a wide range of mixing ratios. The detection limit for DMS is 1–2 ppt in dry air. However, the response is suppressed in the presence of water vapor, so the sample air must be dried or the response must be corrected for this effect. There appeared to be no consistent effect of altitude/pressure on instrument response. The mass spectrometer was installed on the Battelle Gulf stream G‐1 research aircraft and used to monitor DMS and a number of other chemicals during flights over the western North Atlantic Ocean in August and September, 1992. DMS mixing ratios ranged from <2 ppt to 332 ppt, and were highly variable both horizontally and vertically. Vertical profiles indicated that there are times when the marine boundary layer is stratified by one or more temperature inversions, and that DMS emitted by surface seawater can be confined near the surface within a shallow layer a few hundred meters deep. Under such circumstances, the DMS photooxidation products may be removed rapidly by deposition, lessening the potential for cloud nucleation. The mean DMS mixing ratio in the boundary layer below the lowest observed temperature inversion was 61 ppt, with a range of 7–332 ppt. DMS measurements in the free troposphere were lower than the boundary layer values, but high enough to suggest significant transport from the boundary layer to the free troposphere. Significant horizontal variability was observed during constant altitude flights in the boundary layer. In one case the DMS mixing ratio was observed to vary with the ocean depth under the flight path, with higher mixing ratios observed over the shallower coastal shelf and undersea banks. In several cases we also observed an apparent association between atmospheric DMS mixing ratio at low elevation and sea surface temperature.

The relationship between DMS flux and CCN concentration in remote marine regions

The relationship between the steady state cloud condensation nuclei (CCN) concentration and the dimethylsulfide (DMS) emission flux in remote marine regions is investigated by modeling the principal gas‐, aerosol‐, and aqueous‐phase processes in the marine boundary layer (MBL). Results are in reasonable quantitative agreement with the available measurements of DMS, SO2, H2SO4, CCN, and condensation nuclei (CN) concentrations in remote marine regions of the globe and suggest that indeed DMS plays a major role in the particle dynamics of the MBL. For sufficiently low DMS fluxes practically all the SO2 produced by DMS photooxidation is predicted to be heterogeneously converted to sulfate in sea‐salt aerosol particles. For DMS fluxes higher than approximately 2.5 μmole m−2d−1 a linear relationship is found to exist between the CCN number concentration and the DMS flux.

Aerosol formation during photooxidation of organosulfur species

Measurements of aerosol formation during the photooxidation of dimethylsulfide (DMS) and dimethyldisulfide (DMDS) in an outdoor smog chamber are compared with predictions from a model of aerosol nucleation and growth in the chemically reacting system. The aerosol is assumed to consist of methanesulfonic acid (MSA), sulfuric acid, and water. Source rates of the two acid species are obtained from a detailed chemical mechanism for the organosulfur precursor oxidation and are used to drive the aerosol model. Good agreement between experiment and predictions was observed for DMDS and DMS oxidation in the presence of NO x , but maximum total number concentrations achieved during DMDS oxidation in the absence of NO x were somewhat underpredicted. The effect upon model predictions of variations in model input parameters is evaluated.

Photooxidation of dimethyl sulfide and dimethyl disulfide. II: Mechanism evaluation

The mechanisms for atmospheric photooxidation of CH3SCH3 and CH3SSCH3 developed in Part I are evaluated by a series of outdoor smog chamber experiments. Measured product yields, including SO2, H2SO4, CH3SO3H and HCHO, are reported. The predictions of the mechanisms developed in Part I are found to be in substantial agreement with the measured concentrations from the smog chamber. By comparison of mechanism predictions and observations, critical uncertainties in the mechanism are identified.

Biogenic sulfur emissions from the Subantarctic and Antarctic Oceans

Measurements of the atmospheric distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), non‐seasalt sulfate (nss‐SO42−), and methylmercaptan (MeSH) were made over the Drake Passage and the coastal and inshore waters west of the Antarctic Peninsula during the 1986 austral fall season. DMS concentrations were also measured in the surface ocean, and vertical profiles were obtained at several locations in the inshore water areas. Surface seawater concentrations of DMS were on the order of 2 nmol L−1, similar to values observed in temperate latitudes. The vertical profiles showed maximum values at depths between 5–40 m. DMS concentrations in the atmosphere were near 4 nmol m−3 (96 parts per trillion by volume, (pptv)), close to the global average for remote oceanic regions. The sea‐to‐air flux of DMS ranged between 1–5 μmol m−2 d−1, with the highest values found in the open ocean areas. The total sea‐to‐air flux of DMS from the Southern Ocean is estimated to be 0.2 Tmol yr −1. MeSH was detected occasionally at concentrations up to 0.15 nmol m−3 (3.6 pptv). The average aerosol MSA concentration (0.27 nmol m−3) was surprisingly high relative to the level of nss‐SO42− (0.31 nmol m−3). Both compounds were found predominantly in fine particles. The nss‐SO42− values were extremely low, comparable to winter values reported for the South Pole. SO2 concentrations were also very low (0.45 nmol m−3 (11 pptv)), consistent with the low levels of nss‐SO42−. The residence time of DMS in the Antarctic marine atmosphere is estimated to be about 2–3 days during clear weather and about 6–7 days during overcast conditions. Photooxidation of DMS in the Southern Ocean atmosphere may lead to a higher yield of MSA and a lower yield of SO2 compared to other world ocean areas.

Formation of sulfur dioxide and methanesulfonic acid in the photooxidation of dimethyl sulfide in the air

Photooxidation of dimethyl sulfide (DMS) in air in the presence of NO was studied. Sulfur dioxide (SO2) and methanesulfonic acid (CH3SO3H) are major sulfur‐containing products. In the reaction systems of DMS‐NO‐air with low initial NO concentration and DMS‐CH3ONO‐air, in which OH radical‐initiated photooxidation prevails, the yield of SO2 was determined to be 20.7 ± 1.2 %. The yield of methanesulfonic acid is more than 50 % of the consumed DMS. Sulfuric acid was also detected as a minor product with a yield of less than 2 %. The implications of these results on the atmospheric sulfur cycle are discussed.