Short-Term Variability of Atmospheric DMS and Its Oxidation Products at Amsterdam Island during Summer Time

A one-month experiment was performed at Amsterdam Island in January 1998, to investigate the factors controlling the short-term variations of atmospheric dimethylsulfide (DMS) and its oxidation products in the mid-latitudes remote marine atmosphere. High mixing ratios of DMS, sulfur dioxide (SO₂) and dimethylsulfoxide (DMSO) have been observed during this experiment, with mean concentrations of 395 parts per trillion by volume (pptv) (standard deviation, = 285, n = 500), 114 pptv ( = 125, n = 12) and 3 pptv ( = 1.2, n = 167), respectively. Wind speed and direction were identified as the major factors controlling atmospheric DMS levels. Changes in air temperature/air masses origin were found to strongly influence the dimethylsulfoxide (DMSO)/DMS and SO₂/DMS molar ratios, in line with recent laboratory data. Methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄ ^2–) mean concentrations in aerosols during this experiment were 12.2± 6.5 pptv (1, n=47) and 59 ± 33 pptv (1, n=47), respectively. Evidence of vertical entrainment was reported following frontal passages, with injection of moisture-poor, ozone-rich air. High MSA/ nss-SO₄ ^2– molar ratios (mean 0.44) were calculated during these events. Finally following frontal passages, few spots in condensation nuclei (CN) concentration were also observed.     

Shipboard measurements of atmospheric dimethylsulfide and hydrogen sulfide in the Caribbean and Gulf of Mexico

Simultaneous shipboard measurements of atmospheric dimethylsulfide and hydrogen sulfide were made on three cruises in the Gulf of Mexico and the Caribbean. The cruise tracks include both oligotrophic and coastal waters and the air masses sampled include both remote marine air and air masses heavily influenced by terrestrial or coastal inputs. Using samples from two north-south Caribbean transects which are thought to represent remote subtropical Atlantic air, mean concentrations of DMS and H₂S were found to be 57 pptv (74 ng S m^-3, =29 pptv, n=48) and 8.5 pptv (11 ng S m^-3, =5.3 pptv, n=36), respectively. The ranges of measured concentrations for all samples were 0–800 pptv DMS and 0–260 pptv H₂S. Elevated concentrations were found in coastal regions and over some shallow waters. Statistical analysis reveals slight nighttime maxima in the concentrations of both DMS and H₂S in the remote marine atmosphere. The diurnal nature of the H₂S data is only apparent after correcting the measurements for interference due to carbonyl sulfide. Calculations using the measured ratio of H₂S to DMS in remote marine air suggest that the oxidation of H₂S contributes only about 11% to the excess (non-seasalt) sulfate in the marine boundary layer.     

DMS and SO2 at Baring Head, New Zealand: Implications for the Yield of SO2 from DMS

Atmospheric dimethyl sulfide (DMS) and sulfur dioxide (SO₂) concentrations were measured at Baring Head, New Zealandduring February and March 2000. Anti-correlated DMS and SO₂ diurnalcycles, consistent with the photochemical production of SO₂ from DMS, were observed in clean southerly air off the ocean. The data is used to infer a yield of SO₂ from DMS oxidation. The estimated yields are highly dependent on assumptions about the DMS oxidation rate. Fitting the measured data in a photochemical box model using model-generated OH levels and the Hynes et al. (1986) DMS + OH rate constant suggests that theSO₂ yield is 50–100%, similar to current estimates for the tropical Pacific.However, the observed amplitude of the DMS diurnal cycle suggests that the oxidation rate is higher than that used by the model, and therefore, that theSO₂ yield is lower in the range of 20–40%.     

A global three-dimensional model of the tropospheric sulfur cycle

The tropospheric part of the atmospheric sulfur cycle has been simulated in a global three-dimensional model. The model treats the emission, transport, chemistry, and removal processes for three sulfur components; DMS (dimethyl sulfide), SO₂ and SO₄ ^2– (sulfate). These processes are resolved using an Eulerian transport model, the MOGUNTIA model, with a horizontal resolution of 10° longitude by 10° latitude and with 10 layers in the vertical between the surface and 100 hPa. Advection takes place by climatological monthly mean winds. Transport processes occurring on smaller space and time scales are parameterized as eddy diffusion except for transport in deep convective clouds which is treated separately. The simulations are broadly consistent with observations of concentrations in air and precipitation in and over polluted regions in Europe and North America. Oxidation of DMS by OH radicals together with a global emission of 16 Tg DMS-S yr^–1 from the oceans result in DMS concentrations consistent with observations in the marine boundary layer. The average turn-over times were estimated to be 3, 1.2–1.8, and 3.2–6.1 days for DMS, SO₂, and SO₄ ^2– respectively.     

Sulfur dioxide and dimethyl sulfide in the central Pacific troposphere

Boundary-layer and free-troposphere measurements of sulfur dioxide, dimethyl sulfide, and carbon disulfide were made during transits of the central and southern Pacific Ocean between Hawaii and Australia. Sulfur dioxide was generally less than 100 pptv and highly variable with no correlation with respect to geographic location or altitude. Dimethyl sulfide in the boundary layer had a concentration range of <10 to 200 pptv. Highest concentrations of DMS were in the equatorial region of the southern hemisphere although the concentrations were dependent on location and meteorological regime. In the region of the Fiji Islands several boundary layer samples had SO₂, DMS, and CS₂. In 1989, additional SO₂ measurements were made between Hawaii and the equator and to the west of Hawaii downwind of the Kilauea volcano plumes.Paper submitted to the 7th International Symposium of the Commission for Atmospheric Chemistry and Global Pollution on the Chemistry of the Global Atmosphere held in Chamrousse, France, from 5 to 11 September 1990.     

Aircraft Measurements of Dimethyl Sulfide (DMS) Using a Whole Air Sampling Technique

We present a technique for the measurement of dimethyl sulfide (DMS) from airborne and ground-based platforms, using whole air sampling followed by gas chromatography with mass spectrometer and flame ionization detection. DMS measurements that were obtained during the 1999 NASA Pacific Exploratory Mission-Tropics B showed excellent agreement with independent in-flight DMS measurements, over a wide range of concentrations. The intercomparison supports two key results from this study, first that DMS can be accurately quantified based on ethane and propane per-carbon-response-factors (PCRFs), and second that DMS is stable in water-doped electropolished stainless steel canisters for at least several weeks. In addition, our sampling frequency and duration are flexible and allow detail in the vertical structure of DMS to be well captured. Sampling times as fast as 8 s were achieved and these data are suitable for DMS flux calculations using the mixed-layer gradient technique. Correlations between DMS and other marine tracers can also be readily investigated by this whole air sampling technique, because DMS is analyzed together with more than 50 simultaneously sampled hydrocarbons, halocarbons, and alkyl nitrates. The detection limit of the DMS measurements is 1 part per trillion by volume (pptv), and we conservatively estimate the accuracy to be ±20% or 3 pptv, whichever is larger. The measurement precision (1 ) is 2–4% at high mixing ratios (> 25 pptv), and 1 pptv or 15%, whichever is larger, at low mixing ratios (<10 pptv).     

Vertical distribution of dimethylsulfide,sulfur dioxide,aerosol ions,and radon over the Northeast Pacific Ocean

Dimethylsulfide (DMS), sulfur dioxide (SO₂), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO₄ ^2–), sodium (Na⁺), ammonium (NH₄ ⁺), and nitrate (NO₃ ^–) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m^–3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m^–3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.The atmospheric SO₂ concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m^–3 (STP). The nonsea-salt sulfate (ns-SO₄ ^2–) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO₂ and nss-SO₄ ^2– from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a sea-salt inversion layer was reflected in the profiles of those aerosol components, e.g., Na⁺ and NO₃ ^–, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently remote northern hemispheric regions.     

Airborne measurements of dimethylsulfide,sulfur dioxide,and aerosol ions over the Southern Ocean South of Australia

Vertical distributions of dimethylsulfide (DMS), sulfur dioxide (SO₂), aerosol methane-sulfonate (MSA), non-sea-salt sulfate (nss-SO₄ ^2-), and other aerosol ions were measured in maritime air west of Tasmania (Australia) during December 1986. A few cloudwater and rainwater samples were also collected and analyzed for major anions and cations. DMS concentrations in the mixed layer (ML) were typically between 15–60 ppt (parts per trillion, 10^–12; 24 ppt=1 nmol m^–3 (20°C, 1013 hPa)) and decreased in the free troposphere (FT) to about <1–2.4 ppt at 3 km. One profile study showed elevated DMS concentrations at cloud level consistent with turbulent transport (cloud pumping) of air below convective cloud cells. In another case, a diel variation of DMS was observed in the ML. Our data suggest that meteorological rather than photochemical processes were responsible for this behavior. Based on model calculations we estimate a DMS lifetime in the ML of 0.9 days and a DMS sea-to-air flux of 2–3 mol m^–2 d^–1. These estimates pertain to early austral summer conditions and southern mid-ocean latitudes. Typical MSA concentrations were 11 ppt in the ML and 4.7–6.8 ppt in the FT. Sulfur-dioxide values were almost constant in the ML and the lower FT within a range of 4–22 ppt between individual flight days. A strong increase of the SO₂ concentration in the middle FT (5.3 km) was observed. We estimate the residence time of SO₂ in the ML to be about 1 day. Aqueous-phase oxidation in clouds is probably the major removal process for SO₂. The corresponding removal rate is estimated to be a factor of 3 larger than the rate of homogeneous oxidation of SO₂ by OH. Model calculations suggest that roughly two-thirds of DMS in the ML are converted to SO₂ and one-third to MSA. On the other hand, MSA/nss-SO₄ ^2- mole ratios were significantly higher compared to values previously reported for other ocean areas suggesting a relatively higher production of MSA from DMS oxidation over the Southern Ocean. Nss-SO₄ ^2- profiles were mostly parallel to those of MSA, except when air was advected partially from continental areas (Africa, Australia). In contrast to SO₂, nss-SO₄ ^2- values decreased significantly in the middle FT. NH₄ ⁺/nss-SO₄ ^2- mole ratios indicate that most non-sea-salt sulfate particles in the ML were neutralized by ammonium.     

Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere

A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO ₄ ^2– ) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH₃SCH₃) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH₃SO₃H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO ₄ ^2– toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO₂). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO₂ is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO₃) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO₂, MSA, and nss-SO ₄ ^2– are almost independent of NO _x concentration and radiation field. If dimethylsulfoxide (DMSO or CH₃S(O)CH₃) is produced by the addition reaction and further converted to sulfuric acid (H₂SO₄) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO ₄ ^2– at high latitudes.     

Seasonal variations of atmospheric sulfur dioxide and dimethylsulfide concentrations at Amsterdam Island in the southern Indian Ocean

Daily measurements of atmospheric sulfur dioxide (SO₂) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (²²²Rn) as continental tracer. Average monthly SO₂ concentrations range from less than 0.2 to 3.9 nmol m^-3 (annual average = 0.7 nmol m^-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO₂ concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO₂ concentrations within ±30%. Comparing between computed and measured SO₂ concentrations allowed us to estimate a yield of SO₂ from DMS oxidation of about 70%.     

Determination of trace aqueous dimethylsulfoxide concentrations by isotope dilution gas chromatography/mass spectrometry: Application to rain and sea water

A method has been developed for determining trace quantities of dimethyl sulfoxide (DMSO) in aqueous solutions using isotope dilution gas chromatography/mass spectrometry. The method consisted of first reducing DMSO to dimethyl sulfide (DMS), followed by purge and trap preconcentration of DMS. The concentration of DMSO was determined from the signal ratio obtained for the parent ions of DMS and d₆-DMS, and the known aqueous concentration of d₆-DMSO. The precision of this method was determined to be ± 2.9 %, based on replicate DMSO determinations of a test solution prepared by adding isotopically unenriched (h₆-DMSO) to distilled water. The detection limit was 0.010 nmoles/L for the sampling conditions used in this study. This method was applied to the determination of DMSO concentrations in both rain and sea water. The concentration of DMSO in rain was found to be in the range of 2–4 nmoles/L for samples collected at an inland location (Phila, PA) and 8–11 nmoles/L for samples collected at a coastal location (Lewes, DE). Determination of DMSO in sea water required special sample preparation steps to eliminate positive interferences. A depth profile of DMS, DMSO, and dimethyl sulfoniopropionate (DMSP) concentrations is reported for sea water collected off the coast of Ocean City, Md, in August, 1990     

Sources,transport, and sinks of SO<Subscript>2</Subscript> over the equatorial Pacific during the Pacific Atmospheric Sulfur Experiment

The Pacific Atmospheric Sulfur Experiment (PASE) is the first sulfur-budget field experiment to feature simultaneous flux measurements of DMS marine emissions and SO₂ deposition to the ocean surface. We make use of these data to constrain a 1-D chemical transport model to study the production and loss pathways for DMS and SO₂ over the equatorial Pacific. Model results suggest that OH is the main sink for DMS in the boundary layer (BL), and the average DMS-to-SO₂ conversion efficiency is ~73%. In an exploratory run involving the addition of 1 pptv of BrO as a second oxidant, a 14% increase in the DMS flux is needed beyond that based on OH oxidation alone. This BrO addition also reduces the DMS-to-SO₂ conversion efficiency from 73% to 60%. The possibility of non-DMS sources of marine sulfur influencing the estimated conversion efficiency was explored and found to be unconvincing. For BL conditions, SO₂ losses consist of 48% dry deposition, while transport loss to the BuL and aerosol scavenging each account for another 19%. The conversion of SO₂ to H₂SO₄ consumes the final 14%. In the BuL, cloud scavenging removes 85% of the SO₂, thus resulting in a decreasing vertical profile for SO₂. The average SO₂ dry deposition velocity from direct measurements (i.e., 0.36 cm sec⁻¹) is approximately 50% of what is calculated from the 1-D model and the global GEOS-Chem model. This suggests that the current generation of global models may be significantly overestimating SO₂ deposition rates over some tropical marine areas. Although the specific mechanism cannot be determined, speculation here is that the dry deposition anomalous results may point to the presence of a micro-surface chemical phenomenon involving partial saturation with either S(IV) and/or S(VI) DMS oxidation products. This could also appear as a pH drop in the ocean’s surface microfilm layer in this region. Finally, we propose that the enhanced SO₂ level observed in the lower free troposphere versus that in the upper BuL during PASE is most likely the result of transported DMS/SO₂-rich free-tropospheric air parcels from the east of the PASE sampling area, rather than an inadequate representation in the model of local convection.     

Field study of dimethylsulfide oxibation in the boundary layer: Variations of dimethylsulfide,methanesulfonic acid,sulfur dioxide,non-sea-salt sulfate and aitken nuclei at a coastal site

Measurements of atmospheric dimethylsulfide (DMS) and its oxidation products, sulfur dioxide (SO₂), methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄ ^2-) were monitored during the period June 9–26, 1989 at a coastal site in Brittany. As indicated by the radon (Rn-222) activities and the high concentrations of NOx the air masses, for most of the experiment, were continental in origin. The observed concentrations range from 1.9 to 65 nmol/m³ for DMS (n=157), 0.6 to 94.2 nmol/m³ for SO₂ (n=50), 0.6 to 11.6 nmol/m³ for MSA (n=44) and 42 to 350 nmol/m³ for nss-SO₄ ^2- (n=44). Aitken nuclei reached values as high as 4.5 × 10⁵ particles/m³. When continental conditions predominated, the measured SO₂ concentrations were lower than those expected from a consideration of the observed DMS concentrations and the existence of SO₂ background of the continental air masses. Similarly, compared to the MSA/DMS ratio in the marine atmosphere, higher concentrations of MSA were observed than those expected from the measured levels of DMS. The presence of enhanced levels of MSA was also endorsed by the observation that the measured mean MSA/nss-SO₄ ^2- ratio of 6±3% was similar to the mean value of 6.9% observed in the marine atmosphere. These above observations are in line with recent laboratory findings by Barnes et al. (1988), which show an increase of the MSA/DMS yield with a simultaneous decrease of the SO₂/DMS yield in the presence of NOx.     

DMS and SO2 Measurements in the Tropical Marine Boundary Layer

Dimethyl sulfide (DMS) and sulfur dioxide (SO₂) mixing ratios were measured in the boundary layer on Oahu, Hawaii in April and May 2000. Average DMS and SO₂ levels were 22 ± 7 (n = 488) pmol/mol and 23 ± 7 (n = 471) pmol/mol respectively. Anti-correlated DMS and SO₂ diurnal cycles, consistent with DMS + OH oxidation were observed on most days. Photochemical box model simulations suggest that the yield of SO₂ and total SO₂ sink are ∼85% and ∼2 × 10⁴ molec cm^{− 3} s^{− 1} respectively. On several days the rate of decrease in DMS and increase in SO₂ levels in the early morning were larger that predicted by the model. Dynamical and chemical causes for the anomalous early morning data are explored.     

The vertical sulfur dioxide distribution at the tropopause level

In 1978–1980 nine aircraft flights to an altitude of up to 15 km were made over western Europe. Sulfur dioxide was measured with a sensitive chemiluminescence method consisting of separate sampling and analysis stages and application of a wet chemical filter procedure (detection limit: 8 pptv SO₂).The measurements performed in the upper troposphere and lower stratosphere lead to some unexpected results: (a) the meteorological conditions at the tropopause level have an important influence on the observed SO₂ mixing ratio; (b) between the 500 mb and the actual tropopause level the SO₂ mixing ratio is found to be <100 pptv, and weak vertical gradients of SO₂ suggest only a small flux of tropospheric SO₂ into the stratosphere; (c) increasing SO₂ mixing ratios within the first kilometers of the stratosphere give strong support to a stratospheric source of SO₂.In the light of improved one-dimensional models considering the vertical distribution of stratospheric sulfur compounds (Crutzen, 1981; Turco et al. 1981) it can be shown that the oxidation of organic sulfur compounds (e.g., OCS, CS₂) seems to be a stratospheric source of SO₂. Furthermore, the flux calculations based on the SO₂ mixing ratios measured at the tropopause level indicate that the contribution of tropospheric (man-made) SO₂ to the stratospheric aerosol layer is of only minor importance.     

Measurements of atmospheric dimethyl sulfide and carbon disulfide in the western Atlantic boundary layer

Shipboard measurements of atmospheric dimethyl sulfide were made during two transects along the east coast of the United States and at several stations in the Gulf of Maine. Limited measurements of carbon disulfide and hydrogen sulfide are also reported. The mean DMS mixing ratio was 29 pptv (=25, n=84, median 19 pptv) during the Atlantic transects, and 101 pptv (=67, n=77, median 79 pptv) in the Gulf of Maine. Distinct diurnal variations were found in the DMS data from the transects. The meteorology of the study area appears to control day-to-day differences in the magnitude of these diurnal variations, although rapid daytime oxidation is suggested in some cases. Diurnal variations were also evident in near-shore stations in the Gulf of Maine due to nocturnal boundary-layer inversion. Diurnal variation was not evident at other sites in the Gulf due to large scale changes in the atmospheric circulation pattern, which effectively masked any effects due to oxidation processes. Model simulations confirm that the DMS levels and diurnal variation found during the transects are not consistent with atmospheric oxidation processes alone. Atmospheric CS₂ and H₂S mixing ratios were less than 3 pptv during the transects, except for a single period of higher CS₂ mixing ratios (reaching 11 pptv) during advection of continental air. Calculations of the flux of oceanic sulfur to the eastern United States show that the contribution of natural sulfur to the North American sulfur budget is small compared to anthropogenic sources.     

FT-IR Study of the Kinetics and Products of the Reactions of Dimethylsulphide, Dimethylsulphoxide and Dimethylsulphone with Br and BrO

Kinetics and products of the gas-phase reactions of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO₂) with Br atoms and BrO radicals in air have beeninvestigated using on-line Fourier Transform Infrared Spectroscopy (FT-IR) as analytical technique at 740 ± 5 Torr total pressure and at 296 ± 3 K in a480 L reaction chamber. Using a relative rate method for determining the rate constants; the following values (expressed in cm³molecule^–1 s^–1) were found: k_DMS+Br = (4.9 ±1.0) ×10^–14, k_DMSO + Br < 6 × 10^–14,k_{DMSO 2} + Br 1 × 10^–15,k_DMSO + BrO = (1.0 ± 0.3) × 10^–14 andk_{DMSO 2} + BrO 3 × 10^–15 (allvalues are given with one on the experimental data). DMSO, SO₂, COS, CH₃SBr andCH₃SO₂Br were identified as the main sulphur containing products of the oxidation of DMS by Br atoms. From the reaction between DMSO and Br atoms, DMSO₂and CH₃SO₂Br were the only sulphur containing products thatwere identified. DMSO, DMSO₂ and SO₂ were identified as themain sulphur containing products of the reaction between DMS and BrO.DMSO₂ was found to be the only product of the reaction between DMSO and BrO. For the reactions of DMSO₂ with Br and BrO no products were identified because the reactions were too slow.The implications of these results for atmospheric chemistry are discussed.     

Emissions of marine biogenic sulfur to the atmosphere of northern Europe

Measurements of DMS and other reduced sulfur compounds in surface waters have been carried out from a helicopter in the seas surrounding Scandinavia. Average summer time concentrations of DMS ranged from 70 to 150 ngS L^-1. Simultaneous measurements of biological and physical parameters revealed no correlation between DMS and phytoplankton species, species assemblages, total phytoplankton biomass, chlorophyll a, temperature, and salinity. The only exception was a correlation between DMS concentration, Chrysochromulina spp. belonging to the Prymnesiophyceae, and salinity over a narrow range of salinity in the Baltic Sea.The flux of reduced sulfur to the atmosphere in July in this region is estimated to be 120–170 gS m^-2 d^-1 from the Baltic, 240–810 in the Kattegat/Skagerrak, and 120–690 in the North Sea. Annual fluxes are roughly 100 times higher than these daily fluxes. On an annual basis, biogenic sulfur emissions from the coastal seas are negligible (<1%) compared to the anthropogenic emissions in northern Europe. However, during the summer months, the biogenic sulfur emissions from the seas surrounding the Scandinavian peninsula are estimated to be as high as 20–70% of the anthropogenic emissions in Scandinavia. This makes it of interest to incorporate the biogenic emissions in calculations of long-range transport and deposition of sulfur within the region.Other volatile sulfur species, mainly methyl mercaptan, contribute about 10% of the total flux of reduced sulfur. Estimated fluxes of CS₂ to the atmosphere ranged from 1 gS m^-2 d^-1 in the Baltic Sea to 6 gS m^-2 d^-1 in the North Sea. No emissions for H₂S or COS were detected.     

Chemical Composition of Wet Precipitation in Irbid, Jordan

Rainwater samples were collected in Irbid city using 24 hour sampling periods from December 1996 to April 1998. All samples were analyzed for major cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺), major anions (Cl^–, NO₃ ^– and SO₄ ^2–) and pH. High levels of Ca²⁺ and SO₄ ^2– were observed. Together, Ca²⁺ and SO₄ ^2– made up more than 52.4% of the total ion mass, while Ca²⁺ alone contributed over 39.0% of the total cation. The majority of the rain samples collected had pH values higher than 5.6. The average pH was 6.4±0.9. High values of pH are attributed to the neutralization by natural alkaline local dusts which contain large fractions of calcite. Correlation and mineralogical analyses indicated that Ca²⁺, K⁺ and fractions of Na⁺, SO₄ ^2– and Mg²⁺ are of crustal origin. Results of the present study suggested that the atmospheric composition in the city is strongly influenced by natural sources rather than anthropogenic.     

Low-level atmospheric sulfur dioxide measurement using HPLC/fluorescence detection

An automated technique for measuring SO₂ in ambient air has been developed. Air is passed through a gas/liquid exchange coil with an aqueous absorber solution containing 10 µM formaldehyde and 0.84 mM Na₂EDTA. The SO₂ rapidly equilibrates with bisulfite (HSO ₃ ^– ) and sulfite (SO ₃ ^2– ) in the aqueous solution. The aqueous S(IV) is subsequently reacted with o-phthaladehyde in the presence of excess ethanolamine to form a fluorescent isoindole in a continuous flow stream. This derivative is then separated using reversed phase HPLC and detected via fluorescence with excitation and emission wavelengths at 330 and 380 nm, respectively. The lower limit of detection is 7 pptv (S/N=3), with a measurement period of eight minutes per sample. The instrument response is linear over several orders of magnitude.