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1.
The oxidation of carbon disulphide has been studied under conditions which are likely to pertain in the atmosphere. The quantum yield for direct photo-oxidation of CS2 in air at 1 atm pressure, using near UV radiation was 0.012, with OCS as a major product. The rate coefficient (k 1) for the reaction of OH with CS2, was determined from measurements of OCS formation in the near UV photolysis of HONO?CS2?O2?N2 mixtures. k 1 was dependent on oxygen concentration rising from ≤4×10-14 cm3 molecule-1 s-1 at O2≤15 Torr to (2.0±1.0)×10-12 cm3 molecule-1 s-1 at 1 atm air and 300 K. Equimolar amounts of carbonyl sulphide and sulphur dioxide were the major reaction products. The concentration of carbon disulphide in the ambient atmosphere was measured and the concentration to be expected in the background atmosphere was estimated. Rate and concentration data were used to show that carbon disulphide oxidation represents a major source for atmospheric carbonyl sulphide. It can also serve as an alternate source for atmospheric sulphur dioxide in addition to that produced from hydrogen sulphide and dimethyl sulphide. A consideration of atmospheric concentrations and rate data for these trace sulphur gases suggests that the natural sulphur budget is much smaller than the yearly amounts of sulphur dioxide emitted from anthropogenic sources. 相似文献
2.
C2-C6 Nonmethane hydrocarbon (NMHC) concentrations in the atmospheric boundary layer and in surface seawater were simultaneously measured during an oceanographic cruise in the intertropical Indian Ocean. NMHC were found to be mainly C2-C4 alkenes and C2-C3 alkanes. Their concentrations ranged from 1 to 30×10–9 l/l in the seawater and 0.1 to 15 ppbv in the atmosphere. Seawater appeared to be a source because the C2-C6 NMHC were supersaturated with respect to the atmosphere by 2 or 3 orders of magnitude.After a selection of the pure marine atmospheric samples, performed with the help of stable and radioactive continental tracers, we found an identical composition in NMHC of surface air and seawater. This observation enabled us to establish that the gas transfer between sea and air occurred according to nonsteady state processes, and that the fluxes cannot be deduced only from atmospheric measurements. An order of magnitude value of the oceanic source for the different NMHC is however derived from the comparison of their sea water concentrations to that of propane and an independent evluation of the marine source of this last compound. 相似文献
3.
Observations of the Nitrate Radical in the Marine Boundary Layer 总被引：3，自引：0，他引：3
B. J. Allan N. Carslaw H. Coe R. A. Burgess J. M. C. Plane 《Journal of Atmospheric Chemistry》1999,33(2):129-154
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. 相似文献
4.
Seasonal variations in total particle concentrations at five remote Southern Hemisphere sites in Samoa, Tasmania and Antarctica are compared. The dominant particle production mechanism is deduced to be photochemical, with concentrations dictated by the availability of radiation in the eight months centred on the winter solstice. There is little variation with latitude in the mean summer concentrations. The middle troposphere is shown to act as an important reservoir of photochemically-produced particles in Tasmania and probably in the Antarctic. It is suggested that primary-particle production is mainly through the oxidation of dimethyl sulphide and that these particles then act as centres of condensation for sulphuric acid formed by the oxidation of sulphur dioxide. 相似文献
5.
Shuichi Watanabe Hiroshi Yamamoto Shizuo Tsunogai 《Journal of Atmospheric Chemistry》1995,22(3):271-283
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. 相似文献
6.
7.
A. Richter M. Eisinger A. Ladstätter-weißenmayer J.P. Burrows 《Journal of Atmospheric Chemistry》1999,32(1):83-99
Zenith sky observations of BrO over Bremen (53°N) are reported for the period of September 1994 to January 1996. BrO differential slant columns between 90° and 80° solar zenith angle showed a strong seasonal variation between a winter maximum of 1.9·1014 molec/cm2 and a summer minimum of 0.6·1014 molec/cm2. The seasonal variation in BrO twilight values is shown to be inversely correlated with NO2 columns in agreement with current knowledge of gas phase chemistry of bromine. In contrast to model predictions, no significant difference between morning and evening BrO measurements was observed. During a 6 day polar vortex excursion to mid-latitudes OClO could be measured above Bremen indicating chlorine activation in the vortex air. No significant increase in BrO differential slant columns was detected during this time. 相似文献
8.
Gas exchange experiments were conducted in the tropical Atlantic Ocean during a ship expedition with FS Meteor using a small rubber raft. The temporal change of the mixing ratios of CO, H2, CH4 and N2O in the headspace of a floating glass box and the concentrations of these gases in the water phase were measured to determine their transfer velocities across the ocean-atmosphere interface. The ocean acted as a sink for these gases when the water was undersaturated with respect to the mixing ratio in the headspace. The transfer velocities were different for the individual gases and showed still large differences even when normalized for diffusivity. Applying the laminar film model, film thicknesses of 20 to 70 m were calculated for the observed flux rates of the different gas species. When the water was supersaturated with respect to atmospheric CO, H2, CH4 and N2O, the transfer velocities of the emission process were smaller than those determined for the deposition process. In case of H2 and CH4, emission was even not calculable although, based on the observed gradient, the laminar film model predicted significant fluxes at the air-sea interface. The results are interpreted by destruction processes active within the surface microlayer. 相似文献
9.
Equilibria of the marine multiphase ammonia system 总被引：3，自引：0，他引：3
A lack of empirical data has made it difficult to ascertain whether ammonia is in equilibrium between the oceanic, atmospheric gas and atmospheric particle phases in the remote marine environment. Reported here are simultaneous measurements of the saturation concentration of ammonia relative to ammonia concentrations in ocean surface waters; total seawater ammonia; atmospheric gas phase ammonia; and atmospheric particulate-phase ammonium, non-seasalt sulfate, methanesulfonate, and nitrate. Sampling was performed in May of 1987 in the northeast Pacific Ocean environment and in April and May of 1988 in the central Pacific Ocean environment.These measurements were used to determine the degree to which ammonia approached equilibrium between the oceanic and atmospheric gas and aerosol particle phases. The experimental atmospheric gas phase ammonia concentrations were compared with calculated equilibrium concentrations assuming a Henry's law type of partitioning between the gas and condensed phases. Characteristic times of the processes controlling the fate of ammonia in the marine environment also were compared.The measured atmospheric gas phase and oceanic concentrations of ammonia indicate that ammonia is not in a Henry's law equilibrium across the air/sea interface. This disequilibrium is a result of the long air/sea exchange equilibration time relative to the lifetime of ammonia in the atmosphere. Comparison of the calculated equilibrium gas phase ammonia concentrations with the measured gas phase ammonia concentrations shows that attainment of equilibrium between the atmospheric gas and particle phases is a strong function of the chemical composition of the aerosol particles. The data suggest that fully neutralized aerosol particles are not in Henry's law equilibrium with the gas phase while equilibrium is observed for particles with an average ammonium to non-seasalt sulfate molar ratio less than 1.8. 相似文献
10.
利用重庆市巴南区花溪城市站的多种下垫面(石板、水面、泥土、鹅卵石、草地、水泥、沥青等)及裸露空气(裸温)温度观测资料,分析了各下垫面温度及裸温的季、月、日变化特征和变化规律,结果如下:(1)各下垫面温度和裸温具有显著的季、月变化特征,夏季(尤其是7月)最高,春秋次之,冬季最低。各观测项之间温度的差异在夏季最为明显,冬季差异最小;(2)各下垫面温度和裸温日变化趋势与百叶箱气温基本一致。白天,水泥和沥青的温度值较高,日变化幅度最大,夜间水泥温度最高,草地温度最低;(3)无论是连晴高温天气还是连阴雨天气,水面温度的日变化幅度都最小,主要原因是各下垫面中水的热容量最大,水泥和沥青的热容量则相对较小,即在相同的太阳辐射条件下,水面温度变化最小,水泥和沥青温度则变化较大。连阴雨天气下,夜间各观测项之间差异相对明显,且夜间水泥温度一直处于较低位置,这是与连晴高温时的不同之处。 相似文献