Results 1 - 10 of 121
Results 1 - 10 of 121. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Highlights: • Wear rate of nitrided HEAs was lower than that of as-cast HEAs in the same condition. • The wear mechanism of as-cast alloys in air was abrasive wear of oxide particles. • The wear mechanism of the nitrided HEAs in air was adhesive wear and abrasive wear. • The wear mechanism of HEAs in acid rain was abrasive, oxidative and corrosive wear. • The lubrication action of deionized water and acid rain led to the lower wear rate.
[en] Retention of SO42- was investigated in Galician soils throughout an intense regime of acidification. Experiments consisted of the addition of an H2SO4 solution (pH 2.7) to columns of 6 soils of contrasting properties over 1,2 or 5 months. Leachates were obtained continuously throughout the experiment for analysis, and analysis made of the solid fractions after 1, 2 or 5 months. The greatest capacities for retention of SO42- were found in soil developed from serpentine and micaschist; the lowest in soils from granite, slate and sandy sediments. The surface horizons, especially those rich in organic matter, displayed low retention of SO42-. The amount of SO42- adsorbed throughout the experiment depended on the content of crystalline forms of Fe and with the Fe and Al extracted with dithionite-citrate. The low retention of SO42- in the organic horizons and the slightly negative relation with the organic matter suggest an inhibitory effect of the organic matter on the SO42- retention process. Results of the study show that, under conditions of moderate acidity, SO42- retention occurs in the form of adsorption; in strongly acidic conditions, the precipitation of aluminium-sulphate minerals may provide an additional retention mechanism. 41 refs., 3 figs., 4 tabs
[en] The Brazilian sandy coastal plain named restinga is frequently subjected to particulate and gaseous emissions from iron ore factories. These gases may come into contact with atmospheric moisture and produce acid rain. The effects of the acid rain on vegetation, combined with iron excess in the soil, can lead to the disappearance of sensitive species and decrease restinga biodiversity. The effects of iron ore dust deposition and simulated acid rain on photosynthesis and on antioxidant enzymes were investigated in Eugenia uniflora, a representative shrub species of the restinga. This study aimed to determine the possible utility of this species in environmental risk assessment. After the application of iron ore dust as iron solid particulate matter (SPMFe) and simulated acid rain (pH 3.1), the 18-month old plants displayed brown spots and necrosis, typical symptoms of iron toxicity and injuries caused by acid rain, respectively. The acidity of the rain intensified leaf iron accumulation, which reached phytotoxic levels, mainly in plants exposed to iron ore dust. These plants showed the lowest values for net photosynthesis, stomatal conductance, transpiration, chlorophyll a content and electron transport rate through photosystem II (PSII). Catalase and superoxide dismutase activities were decreased by simulated acid rain. Peroxidase activity and membrane injury increased following exposure to acid rain and simultaneous SPMFe application. Eugenia uniflora exhibited impaired photosynthetic and antioxidative metabolism in response to combined iron and acid rain stresses. This species could become a valuable tool in environmental risk assessment in restinga areas near iron ore pelletizing factories. Non-invasive evaluations of visual injuries, photosynthesis and chlorophyll a fluorescence, as well as invasive biochemical analysis could be used as markers.
[en] In this paper a cost-effectiveness analysis is presented for combating emissions of acid precursors. The focus of concern is to reach the environmental quality goal at least cost. Two cost-effective approaches are elaborated. Firstly, the maximum allowable emission of each acid precursor seperately is allocated in a cost-effective way across the economic sectors. Secondly, the maximum allowable emissions of acid precursors are allocated in a cost-effective way across the three considered acid precursors as well as across the economic sectors. It is argued that not only the energy consumption but also the agricultural sector could play an important role in a cost-effective strategy by curtailing its ammonia emissions. 6 refs., 8 figs., 1 tab
[en] A mathematical model of hydrogen fluoride (HF) deposition and accumulation of fluoride in a Eucalyptus rostrata forest has been developed. The model is based on tree physiology and meteorological principles. The data base for the model was derived from a literature survey of the physiological characteristics of E. rostrata and similar eucalyptus species and from current knowledge of meteorological processes in plant canopies
[en] The average deposition rate of sea salt chloride over the world continents is about 10 meq m-2yr-1. Only about 14±1% of chloride in the pollution-corrected world average river is contributed by sea salt aerosols and the rest from the dissolution of evaporites. The significant increase of the ion concentrations in the Mississippi river from the year 1905 to 1987 was caused by anthropogenic inputs such as fossil fuel burning, common salt consumption, and dissolution of carbonate and silicate rocks by acids derived from acid precipitation. 29 refs., 4 figs., 3 tabs
[en] The paper briefly describes past and present research on acid rain in the UK and priorities for future research. Research began on an ad hoc basis following concerns that UK air pollution was affecting Scandinavia and the need for an integrated multi-disciplinery approach was soon realized. The UK Air Quality Research Programme is increasingly using the concepts of critical loads/levels assessments to identify areas of acidification sensitivity to target future research. Priorities for future work include the effects of air pollution on mature trees in the field and the interaction between air pollution and other biotic and abiotic stresses. 5 figs
[en] The Netherlands Environmental Assessment Agency has recalculated the deposition of potential acid and nitrogen in the Netherlands for the period of 1981 through to 2002. Although the Dutch Empirical Acid Deposition Model (DEADM) was used for many years, several changes in the methodology in the course of time led to calculated depositions that were not always comparable. The new approach, fully based on calculations with the Operational Priority Substances (OPS) model, resulted in a deposition data series consistent for the whole 1981 - 2002 period. The recalculated acid deposition came to 10-20% lower, a difference which in absolute numbers comes to a maximum of 1550 mol per hectare per year when compared with the old data for the 1981 to 1987 period. The differences for 1988 through 1993 are just the opposite: recalculated depositions are 5 to 10% higher than in the old data. From 1993 onward differences were only minor. Calculations with OPS showed the acid deposition to decline from 6000 mol per hectare per year in 1981 to 3000 mol per hectare per year in 2002. The deposition of oxidised sulphur (SOx) showed the sharpest decline: minus 75%, down to 400 mol in 2002. The deposition of oxidised nitrogen (NOy) declined by 30%, to 700 mol per ha per year, along with that of reduced nitrogen (NHx), declining from 30% to 1500 mol per ha per year. The resulting nitrogen deposition declined from 3100 mol to 2200 mol, a reduction of 30%
[nl]Het Milieu- en Natuurplanbureau heeft de deposities van potentieel zuur en stikstof in Nederland voor de periode 1981 tot en met 2002 opnieuw berekend. Jarenlang werd hiervoor DEADM, het Dutch Empirical Acid Deposition Model, gebruikt. In de loop van de tijd zijn diverse correcties op DEADM aangebracht. Deze zijn echter door de jaren heen niet altijd consequent uitgevoerd. De berekende deposities van verschillende jaren waren daardoor niet altijd goed vergelijkbaar. De nieuwe aanpak is geheel gebaseerd op berekeningen met het Operationeel Prioritaire Stoffen (OPS) model. De nieuwe berekeningswijze heeft nu over de gehele periode van 1981 tot en met 2002 een consistente reeks van depositiegetallen opgeleverd. De herberekende verzurende depositie is voor de jaren 1981 tot en met 1987 10 tot 20% lager dan volgens de eerdere berekeningen. Het verschil bedraagt maximaal 1550 mol per hectare. Voor de jaren 1988 tot 1993 liggen de verschillen juist andersom: de herberekende depositie is 5 tot 10% hoger dan in de oude berekeningen. Vanaf 1993 zijn de verschillen gering; er zijn daarom geen beleidsconsequenties
[en] The principal geographic variation in acid-base status of 25 deep soil profiles (maximum 2.6 m deep) was investigated along three transects across Sweden. The transects represent gradients in the atmospheric deposition of acidifying compounds. A latent variable describing the acidity of the profile was extracted by Principal Component Analysis (PCA) and found to contain information that could be geographically interpreted. The variable was correlated more strongly with the atmospheric deposition of S (r-0.86) than with groundwater recharge (r-0.30) or base mineral index (r0.45). It was concluded that variation in the deposition of S, in the form of H2SO4, is the main factor responsible for the large geographical differences in acidity in forest soils along transects from west to east in southern and middle parts of Sweden. 14 refs., 4 figs., 1 tab
[en] The Chongqing region located in Sichuan Province of China, comprises a large city, many small towns and rural areas. The region relies heavily on high-sulfur coal for energy production. Atmospheric pollution by sulfur oxides and other compounds from coal burning has become a major issue. Acid rain is observed throughout the region; volume weighted average pH is about 4.30. Average total S deposition for the region is estimated to be about 8 g S m-2yr-1. This paper reports concentrations of major ions in rain, fog, dew and clouds, of SO2 in air and of airborne particles as well as dustfall. The emissions and interactions between important chemical species in air and water droplets are discussed. 29 refs., 9 figs., 15 tabs