The rates and mechanisms of both gas and liquid phase reactions for the oxidation of sulfur dioxide play an important role in the production of atmospheric acids and aerosol particles. Rhodeet al. (1981) concluded that sulfate production rates were highly non-linear functions of sulfur dioxide emission rates. Their modelling study used an HOx termination mechanism for the HO—SO2 reaction in the gas-phase. Stockwell and Calvert (1983) determined that one of the products of the overall reaction of HO with sulfur dioxide was an HO2 radical. The National Research Council (1983) using a version of the Rhodeet al. (1981) model modified to include HO2 production from the HO—SO2 reaction concluded that sulfate production becomes much more linear with respect to reductions in sulfur dioxide emissions. However, the cause of this increased linearity was not explained by the National Research Council report. It is demonstrated that the increased linearity is due to the coupling of gas-phases and aqueous phase chemistry. The gas-phase sulfur dioxide oxidation mechanism has a very significant effect on hydrogen perodide production rates. 相似文献
Salt-loaded effluents were introduced into the river Wipper during the mining period for almost a century. Beginning with the year 1990, the waste water load was strongly reduced due to the termination of the potash industry. Prior to 1990, monthly means of the chloride concentrations at times exceeded 6,000 mg l−1 in the strongly polluted sections. Maximum concentrations reached twice these values. Up to 1998, mean annual chloride concentrations decreased to values below 2,000 mg l−1. This led to more balanced fluctuations in salinity which had been pronounced before, depending on discharge and short-term changes in production. Similarly, the physiologically adverse ion conditions improved due to decrasing potassium and increasing calcium proportions.
In 1963/64, 1986 and 1998, samples of epilithic, epiphytic and epipsammic diatoms were taken at locations of different salinities along the river and examined for the effects of the salinization on the structure of the diatom assemblages. These structures changed in dependence on salinity. Increasing salt concentrations coincided with decreasing oligohalophilic and increasing mesohalophilic and polyhalophilic species numbers. Above a chloride concentration of about 3,000 mg l−1, the proportion of the latter exceed that of the former (halobion index > 50). Corresponding to different conditions of salinization along the river, characteristic diatom assemblages occur differring from each other and which are specific for the river section. Spring and autumn aspects of the diatom assemblages show also salt-dependent differences. The assemblages found in 1998 after decrease of salinization have changed markedly in comparison to those from 1963/64 and 1986. Halobiontic species predominating formerly occurred only occasionally or not at all. They were replaced by oligohalobic-indifferent forms.
An ecological assessment of the changes was performed based on the halobion index calculated from all the samples. For the strongly salinized section of the river Wipper, a shift from -mesohalobic/polyhalobic conditions in 1963/64 and 1986 to -oligohalobic/β-mesohalobic conditions in 1998 was found. However, constant -oligohalobic conditions are still not given. With regard to the transition from -oligohalobic (limnetic) to β-mesohalobic (brackish) conditions, a maximum chloride concentration of 600 mg l−1 was found. To guarantee -oligohalobic conditions, a maximum chloride concentration of 400 mg l−1 should not be exceeded. 相似文献
The Pimpama River floodplain has developed over the last several thousand years as a result of sea-level fluctuations that
shaped the lower catchment and enabled the formation of sedimentary pyrite. The subsequent production of sulfuric acid due
to the oxidation of this pyrite enhances the breakdown of metal-bearing sediments and can lead to leaching of major and trace
metals into the waters of the region. The seasonal pattern of rainfall and current land-use activities are important aspects
that intensify the natural production of acid and influence the release and distribution of metals. To identify the source
and migration of metals in the Pimpama catchment and to understand the impact of pyrite oxidation on the distribution of metals
in sediments and waters, several components of the drainage system were analyzed: bedrock, sediments from river bed and bank,
and water. The elements analyzed in this study (V, Cr, Co, Ni, Cu, Zn and Pb) are all present in the bedrock material which
explains their occurrence in the unconsolidated sediments of the floodplain. These metals concentrate in the upper section
of the sedimentary sequence and their presence is related to clay minerals such as smectite, organic matter and iron phases.
However, Zn, Mo and Co occur in higher amounts than the local background and within standard shale. This comparison suggests
that the diagenetic processes alone cannot explain the higher concentrations and it is concluded that these metals also have
an anthropogenic source. The formation of sulfuric acid creates conditions for higher mobility of some metals, such as Cr,
Co, Ni, Cu, Zn, but does not affect less mobile ones such as Mo and Pb. Over the longterm, the production of acid influences
the breakdown of mineral phases and enhances the process of weathering. Over the short term, every rain event leaches acid
from sediments and mobilizes metals resulting in a substantial reduction in the quality of river water.
Received: 2 October 1998 · Accepted: 16 February 1999 相似文献
Simultaneous measurements of rain acidity and dimethyl sulfide (DMS) at the ocean surface and in the atmosphere were performed at Amsterdam Island over a 4 year period. During the last 2 years, measurements of sulfur dioxide (SO2) in the atmosphere and of methane sulfonic acid (MSA) and non-sea-salt-sulfate (nss-SO42-) in rainwater were also performed. Covariations are observed between the oceanic and atmospheric DMS concentrations, atmospheric SO2 concentrations, wet deposition of MSA, nss-SO42-, and rain acidity. A comparable summer to winter ratio of DMS and SO2 in the atmosphere and MSA in precipitation were also observed. From the chemical composition of precipitation we estimate that DMS oxidation products contribute approximately 40% of the rain acidity. If we consider the acidity in excess, then DMS oxidation products contribute about 55%. 相似文献
INTRODUCTIONSulfate attack is one of the reasons for concretestructures deteriorating earlier than usual,thusshowing poor durability.The SO42-from the sur-rounding environment such as ocean,saline,groundwater,and even the concrete itself,reacts with thehydration products of cement,whichleads to the de-terioration of the concrete(Li et al.,2000;Kang,1995;Neville,1983;Samarai,1976).The deteriora-tionincludes three processes:the external swelling,cracking,peeling,and disjointing caused by … 相似文献
Global distributions of carbonyl sulfide and carbon disulfide have been calculated with a three-dimensional global model of the atmospheric general circulation (ECHAM). The model calculates a global sink strength for carbonyl sulfide of 0.3 Tg S yr-1, with vegetation uptake being the largest sink. With this sink strength, the sources have to be close to the lower limit of the present estimate in the literature. The calculated mixing ratios are higher in the Southern Hemisphere than in the Northern Hemisphere. This interhemispheric gradient is the opposite of what is observed demonstrating that the present knowledge of the distribution of sinks and sources is not fully adequate. The model calculations support the idea that the open oceans could act as a net sink of carbonyl sulfide. The calculated stratospheric photolysis of carbonyl sulfide constitutes about 4% of the total sink of carbonyl sulfide. A stratospheric production of sulfate from carbonyl sulfide of 0.013 Tg S yr-1 is obtained, which is 3 to 12 times less than what is needed to maintain the stratospheric sulfate aerosol layer. Although these results are associated with uncertainties, due to the low upper boundary and coarse vertical resolution of the model, they support recent findings of a low stratospheric production of sulfate from carbonyl sulfide. Instead, sulfur dioxide transported from the troposphere is calculated to be the most important precursor for the stratospheric sulfate aerosol layer. 相似文献