A Wind Tunnel Study of Gaseous Pollutants in City Street Canyons

Steady state mean concentrations of tracer gas were measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 6.8 ft/sec. The tracer gas was released from two parallel line sources to simulate lanes of traffic in an effort to quantify the persistence of pollution as well as the mean values realized at street levels. An aerodynamically rough turbulent boundary layer of neutral thermal stratification was employed to simulate the atmosphere. Values of concentration measured in the model city were converted to prototype concentrations in ppm and compared to National Ambient Air Quality Standards. It was shown that single isolated structures may cause favorable mixing of pollution downwind but very high concentrations exist in the immediate leeward vicinity of the building. Two favorable geometries for city blocks tested were found to reduce pedestrian exposure to pollution both near heavy traffic congestion and downwind. It was concluded that the pollutant dilution was controlled by the mean flow rather than by turbulent diffusion and that the lateral spread of the plume was slight as one proceeded downwind of the line source. The combination of favorable geometry and higher dilution velocities may bring pollution levels down to existing Air Quality Standards. The body of information presented in this paper should interest city planners and air quality monitoring personnel, as well as those researchers attempting to study and model flow in city street canyons. It provides order of magnitude estimates on pedestrian and office worker exposure to pollutants under a wide range of conditions.     

The Impact of Gold Smelter Emissions on Vegetation and Soils of a Sub-Arctic Forest-Tundra Transition Ecosystem

Gold smelters near Yellowknife in Canada's Northwest Territories have emitted large quantities of sulfur dioxide and arsenic since inception of roasting in 1941. Although particulate wastes are well contained by baghouse fitters in the one remaining operating smelter, significant gaseous emissions continue. Soil and vegetation were sampled at 52 sites over an area of about 40 km radius from the source. Plant ecology was studied at 43 of those sites. After preliminary multi-element screening that indicated only arsenic was a serious persistent contaminant, x-ray fluorescence was used to measure arsenic content in sampled materials. The plant ecology data were synthesized into an Index of Vitality with numerical ratings of pertinent factors. In the marginal forests and rocky outcrops of the area, indicator species of vegetation permitted a division into zones of severe, moderate, mild, or no impact in order of increasing distance from the current center of emissions. Severe impact, including killing of trees, is local only. Analyses of foliage indicate little uptake of arsenic which, together with the presence of S0₂ symptoms, point to S0₂ as the main factor causing decline of vegetation. A separate study, abstracted here, supports this view by providing data that show a frequency of at least 2 significant fumigation episodes per growing season. Soil analyses indicate extremely high arsenic contamination near the stack. A monotonie pattern of dispersion yielded a function explainable in terms of rapid condensation of gaseous emissions. The relationship of arsenic in surface soil and vegetation to distance is approximately an inverse square.     

The Inadequacy of PSD Increments to Protect Visibility in Class I Areas

This study includes an application of the first two phases of a new three-phased decision-making structure that was developed to overcome the problems related to ecological safety and social justice in site selection applications. It was conducted on a current site selection problem related to the municipal solid waste disposal facilities in Kocaeli, the most industrialized region of Turkey. In order to assess the deficiencies of the legal site selection procedures related to ecological safety, two different decision tree modes were applied separately. The first mode (“Legislation”) concerns the current buffer zone applications given in the regulations, while the second one (“Proposed”) includes the applications of the new decision-making structure proposed in this study. Since it was assumed that the subjective tendencies of the decision makers on the weightings would have a significant effect on the final decision, these two modes were assessed by employing two different weighting models. The results were obtained from all of the scenarios related to selection of suitable sites with three different area requirements (15, 250, and 500 acres) for the solid wastes generated in the Kocaeli region. The results showed that the possible changes in the decision structure could cause significant differences in the final decision related to selection of the most suitable sites. The most highest and lowest differences were at the “Legislation” mode for 15 acres and 500 acres, respectively. Furthermore, the results obtained in the study showed that the possible differentiations in the criteria weightings could also cause significant differences in the suitability ranking. Therefore, to get a reliable final decision, a statistical assessment of these differentiations should be made.

Implications: The results showed that the possible changes in the decision structure could cause significant differences in the final decision related to selection of the most suitable sites. Furthermore, the results obtained in the study showed that the possible differentiations in the criteria weightings could also cause significant differences in the suitability ranking. Therefore, to get a reliable final decision, a statistical assessment of these differentiations should be made.     

Theory for Penetration in A Pulse-Jet Cleaned Fabric Filter

Presently, there is no effective way to interpret or predict dust penetration through a pulse-jet cleaned fabric filter. This paper presents a model which considers penetration straight through the filter and penetration by seepage. A considerable number of studies have been devoted to penetration by the straight through process; however, a comparison of data from the literature with the present model indicates that seepage and not straight through penetration accounts for virtually all penetrating dust. Although insufficient information is presently available to use the model to predict penetration, the model does show trends that should occur with changes in filter operating variables such as filtration velocity and pulse pressure, and suggests areas in which further research is necessary.     

A Comparison of Mass,Lead, Sulfate,and Nitrate Concentrations in a Field Study Using Dichotomous,Size-Selective,and Standard Hi-Vol Samplers

Air monitoring In the San Francisco Bay Area was carried out to measure outdoor community air concentrations of poly cyclic aromatic hydrocarbons (PAH) and mutagenlc activity (mutagenlclty) In participate organic matter (POM). Monitoring began In 1979 and Is currently conducted at six stations. PAH and mutagenlclty tests were performed on organic extracts prepared from high volume (hl-vol) filters composited every four months, by meteorological season. PAH were determined by high pressure liquid chromatography (HPLC) with fluorescence and ultraviolet detection. Mutagenlclty was measured In the Ames Salmonella bloas-say using strain TA98 with and without metabolic activation. The nine-year mean concentration of benzo(a)pyrene (BaP) was 0.4 ng/m³. The mutagenlcfty of this amount of BaP accounted for only about 0.2% of the observed mutagenicity In POM and other measured PAH accounted for even less. Concentrations of PAH and mutagenlclty were three to nine times higher during the winter than during other seasons. Year-to-year wintertime trends In several PAH were also seen. Early In the 1980s, winter concentrations of BaP and benzo (g,h,i)perylene Increased. However since the mld-1980’s, their concentrations have fallen. The decrease In PAH concentrations may be the result of an Increasing proportion of vehicles with relatively low organic emissions. In contrast to PAH, mutagenlcfty did not show significant year-to-year time trends.     

Testing and Commercialization of Byproduct Dibasic cids as Buffer Additives for Limestone Flue Gas esulfurization Systems

Pilot plant (0.1 MW) tests and utility boiler full scale demonstration (194 MW) of byproduct organic dibasic acids (DBA) as buffer additives to limestone scrubbers have shown performance improvements equivalent to those achieved by the addition of pure adipic acid. Both SO₂ removal efficiency and limestone utilization increased, and no significant operating problems were observed with three of the four DBA tested. Chemical and biological evaluations of scrubber samples taken during the DBA testing indicated no detectable tOxicity or mutagenicity, and no significant environmental impact is expected as a result of DBA addition. Economic estimates indicate that substitution of DBA for pure adipic acid as a buffer additive will result in additive cost savings of 30 % or greater.     

1987 Joint EPRI/EPA Symposium on Stationary Combustion NOX Control

From March 23rd to 26th, 1987, the city of New Orleans hosted 350 attendees, including representatives from 15 foreign countries, at the 1987 Joint Symposium on Stationary Combustion NO_x Control. Cosponsored by the Electric Power Research Institute (EPRI) and the U.S. Environmental Protection Agency (EPA), the symposium provided attendees the opportunity to hear 49 papers in nine sessions covering technological and regulatory developments on NO_x control in the United States and abroad since the May 1985 symposium in Boston. Session topics included general environmental issues, low-NO_x combustion equipment (i.e., low-NO_x burners, reburning, etc.), flue gas treatment, fundamental combustion research, and special issues for cyclone coal-fueled boilers, oil- and gas-fired boilers, and industrial combustion applications.

Advances to the state-of-the-art presented at this symposium include: improved and/or newly applied combustion modifications for pulverized coal-fired boilers; further analyses of reburning, the leading combustion modification option for cyclone-equipped boilers; initial experiences with catalytic flue gas treatment in Europe; studies of NO_x control retrofit options for oil- and gas-fired utility systems; and new technology developments for coal, oil, and gas fueled utility and industrial combustors.

This paper summarizes those presentations that discussed significant changes since May 1985 in areas of potential interest to EPRI and its utility members. Where appropriate, they include our perspectives on the applicability of these newly disclosed findings to utility systems.     

Predicting and Managing the Health Risks of Sour-Gas Wells

The development of sour-gas resources in Canada and the United States has prompted concerns about the public health risks of accidental releases of gas contaminated with hydrogen sulfide (H₂S) from wells. This paper focuses on methods for improving the prediction and management of those risks. Data associated with the health effects of hydrogen sulfide are examined, and it is suggested that sublethal effects should be addressed in risk assessments of sour-gas wells along with the life-threatening effects normally considered. The demarcation of hazard zones around wells can be improved by using a statistical approach for estimating an upper-bound H₂S release rate; this rate can then be used in an atmospheric dispersion model to estimate maximum distances to downwind concentrations for lethal (300 ppmv) and sublethal (50 ppmv) effects resulting from an accidental release. A vertical release is found to have little impact, especially under stable atmospheric conditions; horizontal releases, on the other hand, result in the greatest downwind distances for health impacts. Management of health risks depends on a mix of safety technologies and contingency actions, such as well-ignition options and provision for post-release monitoring and assessment of ambient H₂S concentrations.