Chemical composition of the NH3-HNO3-H2SO4-NaCl system in the atmosphere of Athens,Greece

This paper presents a procedure for estimating the distribution of ionic material in the NH₃-HNO₃-H₂SO₄-NaCl system and applies this procedure in a particular case. The data used were measurements of HNO₃, NH₃, NO ₃ ^– , SO ₄ ^– , NH ₄ ⁺ Cl^– and Na⁺ performed during February 1989 – February 1990 in a central Athens street with high traffic density. According to the procedure, ions combine in the following manner: Na⁺ combines preferentially with SO ₄ ^– , then with NO ₃ ^– , followed by NH ₄ ⁺ with the remaining SO ₄ ^– and then with the remaining NO ₃ ^– to form bisulphates, sulphates and nitrates. The combination procedure showed that the main constituents of the NH₃-HNO₃-H₂SO₄-NaCl system are primarily (NH₄)₂SO₄ and, to a lesser extent, NH₄NO₃ and NH₄HSO₄, with mean and maximum concentrations, during morning hours, (NH₄)₂SO₄: 14.5 (max 46.8), NH₄NO₃: 2.97 (max 23) and NH₄HSO₄: 1.78 (max 40.6) µg m^–3. Lower concentations of Na₂SO₄, NaHSO₄, NaNO₃ and NH₄Cl and very low concentrations of H₂SO₄ are also present, depending on the availability of NaCl. It became apparent from the ionic distribution that there is sufficient NH₃ to neutralize the H₂SO₄ and HNO₃. It was also shown that a significant fraction of the HNO₃, especially on days with high pollution, occurs as aqueous NO ₃ ^– . A number of empirical equations have been proposed, which enable the approximate estimation of the constituents of the NH₃-HNO₃-H₂SO₄-NaCl system from air pollution monitoring data and meteorological parameters.     

Traditional management and conservation of shea trees (<Emphasis Type="Italic">Vitellaria paradoxa</Emphasis> subspecies <Emphasis Type="Italic">nilotica</Emphasis>) in Uganda

Traditional practices are universally recognised as a basis for conservation of biodiversity. However, such practices are often not included in natural resource conservation policies. This study assessed local conservation practices of shea trees (Vitellaria paradoxa) within different farming systems in Uganda and developed conservation guidelines for the species. The assessment involved 300 respondents, 15 focus groups and 41 key informants. Content analysis was used to identify the most important management and conservation practices. Local uses were categorised on the basis of shea tree products while differences in conservation practices were analysed using the Friedman test. The results show that eight shea tree products are used for 36 different purposes. Respondents’ age significantly influenced their knowledge about the shea tree. Traditional conservation practices include on-farm retention during cultivation and the use of folklore (mainly taboos), customs and rituals. Traditional management practices include weeding, bush burning, pollarding and pruning. Based on the current management and traditional conservation practices, a framework for the conservation of shea trees is proposed for integration into conservation policy decisions.     

Forest-user attitudes toward alternative fire management policies

The formulation and implementation of new fire policies in the national forests depend upon public acceptance. A national survey of organized groups of forest users indicates that, contrary to the concern of many forest managers, considerable support exists for flexible fire suppression policies. Forest users are also willing to accept the risk associated with the manager's use of prescribed fire. However, important intergroup differences do exist. Such variation is discussed in relation to a number of socioeconomic variables, general fire knowledge, specific knowledge about the effects of low-intensity fires, and risk preference levels.     

Water chemistry influences on long-term dissolution kinetics of CdSe/ZnS quantum dots

Widespread usage of engineered metallic quantum dots(QDs) within consumer products has evoked a need to assess their fate within environmental systems.QDs are mixed-metal nanocrystals that often include Cd~(2+)which poses a health risk as a nanocrystal or when leached into water.The goal of this work is to study the long-term metal cation leaching behavior and the factors affecting the dissolution processes of mercaptopropionic acid(MPA) capped CdSe/ZnS QDs in aphotic conditions.QD suspensions were prepared in different water conditions,and release of Zn2+and Cd~(2+) cations were monitored over time by size exclusion chromatography-inductively coupled plasm a-mass spectrometry.In most conditions with dissolved 02 present,the ZnS shell degraded fairly rapidly over～1 week,while some of the CdSe core remained up to 80 days.Additional MPA,Zn~(2+),and Cd2+temporarily delayed dissolution,indicating a moderate role for capping agent detachment and mineral solubility.The presence of H_2 O_2 and the ligand ethylenediaminetetraacetate accelerated dissolution,while NOM had no kinetic effect.No dissolution of CdSe core was observed when 02 was absent or when QDs formed aggregates at higher concentrations with 02 present.The shrinking particle model with product layer diffusion control best describes Zn2+and Cd~(2+) dissolution kinetics.The longevity of QDs in their nanocrystal form appears to be partly controlled by environmental conditions,with anoxic,aphotic environments preserving the core mineral phase,and oxidants or complexing ligands promoting shell and core mineral dissolution.