RESEARCH WATCH AIR Greenhouse gas analysis When hydroelectric dams are built, large quantities of greenhouse gases are produced because of flooding and subsequent decomposition of forest biomass. P. M. Fearnside evaluated emissions produced during development and long-term operation of a hydroelectric reservoir and compared them with emissions that would be produced by fossil fuel alternatives. Results indicate that, during its first year of operation, the hydroelectric project produced more emissions than an equivalent-powered fossil fuel plant. In later years of operation, however, this situation was reversed. The author suggests that because emissions are timedependent, the determination of the relative advantage of the two power sources in terms of their effect on global warming should be timeweighted. {Environ. Conserv. 1997, 24(1), 64-75)
Indoor air chemistry Chemical reactions occur among indoor air pollutants, producing products that would not otherwise be present and that are more harmful than the original reactants. C. J. Weschler and H. C. Shields evaluated reactions likely to occur within a time interval compared with the residence time for a packet of indoor air. Within this time frame, reactions occurred involving ozone with nitric oxide, nitrogen dioxide, and hydrocarbons; free radical reactions; thermal breakdown of peroxyacyl nitrates; and nitrogen oxides and gaseous acids with indoor surfaces. Reaction progress depends on indoor air precursor concentrations, temperature, relative humidity, indoor surface area and the kinds of surfaces present. The mechanism of formation of stable reaction products, such as aldehydes, ketones,
Sources of mercury evaluated It is believed that elevated levels of mercury in remote aquatic environments are attributable to long-range atmospheric transport and deposition of mercury from industrial emissions sources. However, evidence in support of this view has been questioned. W. Fitzgerald and colleagues reviewed information used to argue against atmospheric mercury contamination of remote areas. They concluded that, despite prevailing uncertainties, data demonstrate that over many regions of the world, human-related mercury emissions have increased relative to natural sources. Moreover, the latter cannot account for trends in levels of mercury found in remote regions. The authors suggest that large, natural sources of mercury have not been missed, and they cite evidence for anthropogenic mercury contamination. {Environ. Sci. Technol., ,his iissue ,p. .-7)
and organic acids, is described. [Atmos. Environ. 1997, 31 (21), 3487-95)
Lawn mower emissions Although small engines contribute significantly to emissions inventories in nonattainment areas, insufficient data are available to reliably assess the photochemical reactivity and toxicity of pollutants released during their operation. P. Gabele characterized emissions released from 10 four-stroke lawn mower engines of varying ages that were fueled by standard and reformulated gasolines. Emission rates were found to be sensitive to engine age and fuel type. Newer motors using reformulated fuel produced lower CO and VOC emissions than did older engines but had higher NOx emission rates. Emissions produced from engines fueled with reformulated gasolines contained a smaller proportion of aromatic compounds, leading to reduced emissions toxicity. (/. Air Waste Manage. Assoc. 1197, 47, 945-52)
Vehicle emissions test Motor vehicle emissions tests are usually performed in laboratories under standardized conditions to enable intercomparison of test results, but there is uncertainty whether this environment reproduces actual driving conditions.
0013-936X/98/0932-47A$15.00/0 © 1997 American Chemical Society
I. De Vlieger used an onboard monitoring system to measure fuel consumption and emissions of CO, NO,,., and hydrocarbons during on-road vehicle use in realistic situations. Tests were performed using several cars equipped with a catalyst and one that was not. Effects of road type and driving behavior on emissions were evaluated. Results indicate that cars producing low emissions in laboratory tests do not necessarily produce low emissions during actual driving. [Atmos. Environ. 1997, 31 (22), 3753-61)
BIOAVAILABILITY Phenanthrene sequestration It is difficult to evaluate exposure risks if the availability of soil contaminants is not known. J. C. White and co-workers studied how soil properties and environmental stresses—leaching, wetting, and drying periods—affect the sequestration and bioavailability of phenanthrene in soils. The uptake of phenanthrene in earthworms, its mineralization by bacteria, and its extractability from soil samples were monitored under varied test conditions. Results indicate that sequestration is strongly affected by soil properties and environmental factors. Wetting and dry-
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