STUDY ON THE ANALYSIS AND DISTRIBUTION OF DIMETHYL SULFIDE IN THE EAST CHINA SEA

A method is described for determining dimethylI sulfide (DMS) in seawater. DMS was first extractedfrom the seawater using organic reagent, then reverse-extracted by 5% HgCl2. In the laboratory DMS wasreleased by concentrated HCI and finally measured by GC-FPD. The limit of detection me O.05 ng ofS. Measurements of DMS along surface transects and on wtital profibe across the EaSt China Sca (Ers)continental sheif showed tha itS conodIations of S in the surface seawater ranged from 64-180 ng/L andthat itS vertical djstribuion was divided into 3 trpes. Model talculations of a stagnant film show a DMSflux of 10.6 umol/m_2d the air-sea inteIha.     

OCS,H2S,and CS2 fluxes from a salt water marsh

The diurnal-to-monthly behavior of the fluxes of OCS, H₂S, and CS₂ from a mixed-Spartina grass-covered site in a Wallops Island salt water marsh was determined through a series of experiments in August and September, 1982. Absolute flux values were determined for OCS and H₂S, while only relative values were determined for CS₂. The rates of emission of OCS and H₂S were observed to vary diurnally and to be strongly influenced by tides. The time-averaged flux values show that such mixed-Spartina stands are insignificant ( 1%) global sources of H₂S or CS₂ and insignificant contributors to the global OCS cycle (< 1%). These results demonstrate that some marsh regions play a minor role in the global sulfur budget and, consequently, that the inclusion of such areas in extrapolations of measurements of more productive regions could lead to an overestimate of the role of salt water marshes in the global sulfur budget.     

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.     

Photooxidation of dimethyl sulfide and dimethyl disulfide. I: Mechanism development

Detailed theoretical (Part I, this article) and experimental (Part II) investigations are presented for the mechanism of the atmospheric photooxidation of dimethyl sulfide (CH₃SCH₃) and dimethyl disulfide (CH₃SSCH₃). In this paper, comprehensive mechanisms for the atmospheric chemistry of CH₃SCH₃ and CH₃SSCH₃ are developed based on fundamental considerations of all available kinetic and mechanistic information.     

The effect of nitrogen fertilization on the COS and CS2 emissions from temperature forest soils

The net fluxes of carbonyl sulfide (COS) and carbon disulfide (CS₂) to the atmosphere from nitrogen amended and unamended deciduous and coniferous forest soils were measured during the spring of 1986. We found that emissions of these gases from acidic forest soils were substantially increased after nitrogen fertilization. The total (COS+CS₂) emissions were increased by nearly a factor of three in the hardwood stand and were more than doubled in the pine stand. Furthermore, vegetation type appeared to have an influence on which was the dominant sulfur gas released from the forest soils. The added nitrogen caused a dramatic increase in COS emissions from the hardwood stand (a factor of three increase), while CS₂ emissions from this site were not affected. We observed the opposite response in the pine stand; that is, the nitrogen fertilization had no affect on COS emissions, but did stimulate CS₂ emissions (a factor of more than nine increase).     

On the Gas Phase Reactions Between Volatile Biogenic Mercury Species and the Nitrate Radical

Tropospheric mercury is dominated by gas phase species. In this paper, the gas phase reactions between the nitrate radical and volatile biogenic mercury species have been investigated. An upper limit for the gas phase rate coefficient for reaction between elemental mercury and NO₃-radicals was determined to 4 × 10^–15 cm³ molecule^–1 s^–1 by using the fast flow-discharge technique. The reaction between dimethyl mercury and NO₃, previously shown to be rapid, has also been studied in the laboratory with respect to product distribution using FT-IR. The result from the product study is consistent with a transformation of dimethyl mercury into inorganic, divalent mercury. All carbon delivered as dimethyl mercury was transformed into formaldehyde, methanol and methyl peroxynitrate. Hg was observed as a minor (2%) product. By exclusion, HgO is proposed as the mercury-containing product. Thus, the reaction between dimethyl mercury and the nitrate radical is excluded as a source of monomethyl mercury species in the atmosphere.     

Relation between the concentrations of DMS in surface seawater and air in the temperate North Pacific region

The concentrations of DMS were simultaneously measured in both water and air at the sea surface on board a vessel during a trans-Pacific cruise around 40° N in August 1988. Those in the surface seawater varied widely with a mean of 162 ng S/1 and a standard deviation of 134 ng S/1 (n=37), but the variation was not a mere fluctuation and the high concentration (376 ng S/1) was found in the area between 145° W and 170° W. The atmospheric DMS concentration varied more widely with a mean value of 177 ng S/m³ and a standard deviation of 203 ng S/m³ (n=23). The diurnal variation of DMS was not significant in the air near the sea surface. However, the concentrations in the surface water was fairly well correlated with those in the surface air. The correlation coefficient (r ²=0.86) was larger than that between the atmospheric concentration and outflux of DMS (r ²=0.64). These findings mean that the turnover time of DMS in the atmosphere is not extremely short. Based on the linear relation between the atmospheric and seawater DMS, the turnover time of the atmospheric DMS has been calculated to be 0.9 days with an uncertainty of around 50%. The oxidation rate agrees fairly well with that expected from the OH radical concentration in the marine atmosphere.     

Observations of the Nitrate Radical in the Marine Boundary Layer

A study of the nitrate radical (NO3) has been conducted through a series of campaigns held at the Weybourne Atmospheric Observatory, located on the coast of north Norfolk, England. The NO3 concentration was measured in the lower boundary layer by the technique of differential optical absorption spectroscopy (DOAS). Although the set of observations is limited, seasonal patterns are apparent. In winter, the NO3 concentration in semi-polluted continental air masses was found to be of the order of 10 ppt, with an average turnover lifetime of 2.4 minutes. During summer in clean northerly air flows, the concentration was about 6 ppt with a lifetime of 7.2 minutes. The major loss mechanisms for the radical were investigated in some detail by employing a chemical box model, constrained by a suite of ancillary measurements. The model indicates that during the semi-polluted conditions experienced in winter, the major loss of NO3 occurred indirectly through reactions of N2O5, either in the gas-phase with H2O, or through uptake on aerosols. The most important direct loss was via reactions of NO3 with a number of unsaturated nonmethane hydrocarbons. The cleaner air masses observed during the summer were of marine origin and contained elevated concentrations of dimethyl sulfide (DMS), which provided the major loss route for NO3. The box model was then used to investigate the conditions in the remote marine boundary layer under which DMS will be oxidised more rapidly at night (by NO3) than during the day (by OH). This should occur if the concentration of NO2 is more than about 60% that of DMS.     

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.     

间苯二甲酸二甲酯的好氧微生物降解及其生化途径

从红树林污泥中通过富集培养分离到4株细菌,鉴定结果是多杀巴斯德菌(Pasteurella multocida Sa)、产酸克雷伯菌(Klebsiella oxytoca Sc)、少动鞘氨醇单胞菌(Sphingomonas paucimobilis Sy)和嗜中温甲基杆菌(Methylobacterium mesophilicum Sr).在纯培养降解间苯二甲酸二甲酯(DMI)时发现,单一纯菌株不能完全矿化间苯二甲酸二甲酯,而2种或3种纯菌株组成的混合菌可以将220mg·L-1的底物在12d内完全矿化.主要的中间产物有间苯二甲酸一甲酯(MMI)和间苯二甲酸(IA).根据鉴定出的中间产物,DMI的生化降解途径为:DMI→MMI→IA→CO2 H2O.研究结果表明,DMI的2个酯基的水解是决定DMI能否完全矿化的重要步骤,但 2个酯基的酶催化水解反应有差异,由不同的细菌分步来完成,说明是酯酶对不同底物的专性所致;第2个酯基的水解对整个降解过程有决定性作用.