Instruments capable of measuring in situ numbers of particles within specific size ranges covering a particle-diameter spectrum of approximately 0.001 – 10 microns have been employed to continuously monitor the concentration and size-distribution of atmospheric aerosols. The monitoring site was a television tower located on the boundary between Minneapolis and St. Paul, Minnesota. Air samples were drawn from 70, 170, and 500 feet above ground level and analyzed with optical, electrical, and condensation particle counters to obtain a number-size distribution within the 0.001 – 10 micron size range. In addition to the measurement of particle number and size, several micrometeorological parameters were simultaneously monitored. Particle number-size distributions which were measured during periods of temperature inversion are reported
The field of ozone air quality modeling, or as it is commonly referred to, photochemical air quality modeling, has undergone rapid change in recent years. Improvements in model components, as well as in methods of interpreting model performance, have contributed to this change. Attendant with this rapid change has been a growing need for those developing and using air quality models and policy makers to have a common understanding of the use and role of models in the decision making process. This Critical Review highlights recent advances and continuing problem areas in photochemical air quality modeling. Emphasis is placed on the components and input data for such models, model performance evaluation, and the implications for their use in regulatory decisions. 183 refs., 8 figs., 8 tabs.
The Bechtel Confined Zone Dispersion (CZD) process for FGD retrofit situations was tested at two sites: one at a level of 5 MWe; the other at 70 MWe. The CZD process involves injecting a finely atomized slurry of hydrated lime into a straight run of duct between a boiler's air heater and its electrostatic precipitator (ESP). The effect of process variables on SO2 removal and ESP performance was investigated for dolomitic/calcitic lime. Removals of SO2 in excess of 50 percent were achieved for either lime type at the 5 MWe site. A very short duct length limited injection rate at the 70 MWe site, limiting sulfur removals to a maximum of 30 percent. SO2 removal data for both sites were successfully correlated on a common basis. ESP performance was not fully acceptable during lime injection at both sites, but it is felt that optimization of ESP operations should eliminate this problem. Additional testing is recommended to further explore ESP performance and to optimize lime injection parameters. The results obtained to date continue to indicate that the CZD process is an attractive and economical candidate for FGD retrofit situations.
AbstractA multistaged combustion burner design is being evaluated on a 0.6 MW package boiler simulator for in‐furnace NOx control and high combustion efficiency. A low NOx precombustion chamber burner has been reduced in size by approximately a factor of two (from a 600 ms first‐stage residence time to 250 ms), and, for additional NOx control, coupled with [1] air staging, resulting in a three‐stage configuration, and [2] natural gas fuel staging, yielding up to four stoichiometric zones. Natural gas, doped with ammonia to yield a 5.8 percent fuel nitrogen content, was used to simulate a high nitrogen content fuel/waste mixture. In low NOx burner baseline tests, without advanced staging, a 315 ppm NO emission (measured dry, corrected to zero percent O2) was measured, compared with an emission of 1000 ppm measured using a conventional, unstaged burner. Both of the multistaged combustion modifications for additional NOx control reduced NO emissions by an additional 50 percent, to 160 ppm meeting the program goal. However, air staging application resulted in the entire front end of the boiler being fuel‐rich, whereas fuel staging, or reburning, in the boiler required only a small fuel‐rich flame core in the boiler. Further, no boiler penetrations were necessary with reburning modification, as staged fuel and air were injected through the boiler front wall; access for burnout air injection deep into the boiler was necessary for the air staging modification. Thus, the four‐stage configuration, combining the precombustion chamber burner and reburning, appears to be the most promising approach for minimizing NO emissions and maximizing primary fuel/waste destruction.
Remedial options for leaking underground storage tanks were investigated in a joint project of the Electric Power Research Institute and the Underground Storage Tank Committee of the Utility Solid Waste Activities Group. Both existing and emerging technologies were examined. Thirteen remedial techniques were identified and initially characterized as in situ or non-in situ. In situ methods include volatilization, biodegradation, leaching and chemical reaction, vitrification, passive remediation, and isolation or containment. Non-in situ techniques include land treatment, thermal treatment, asphalt incorporation, solidification and stabilization, groundwater extraction and treatment, chemical extraction, and excavation. Soil and groundwater remediation problems have many site-specific considerations which must be considered in choosing an appropriate remedial option; these include cleanup goals, site and contaminant characteristics, cost, exposure pathways, and others. Appropriate remedial techniques are chosen by assessing technical, implementational, environmental and economic considerations of each available option to achieve the desired cleanup goal at the specified site.
The many advances made in air quality model evaluation procedures during the past ten years are discussed and some components of model uncertainty presented. Simplified statistical procedures for operational model evaluation are suggested. The fundamental model performance measures are the mean bias, the mean square error, and the correlation. The bootstrap resampling technique is used to estimate confidence limits on the performance measures, In order to determine if a model agrees satisfactorily with data or if one model is significantly different from another model. Applications to two tracer experiments are described. It is emphasized that review and evaluation of the scientific components of models are often of greater Importance than the strictly statistical evaluation. A necessary condition for acceptance Of a model should be that it is scientifically correct. It Is shown that even in research-grade tracer experiments, data Input errors can cause errors In hourly-average model predictions of point concentrations almost as large as the predictions themselves. The turbulent or stochastic component of model uncertainty has a similar magnitude. These components of the uncertainty decrease as averaging time increases.
A program is described whereby more than 100 US and foreign laboratories have participated in a quality assurance technique meant to improve the accuracy and consistency in the measurement of vehicle exhaust emissions. Every three months each laboratory received as many as four multicomponent gas samples. Analytical measurements were made on 100% of the samples to assure homogeneity. Regardless of analyte or concentration, component consistency checks were typically 0.3% or less.
Audit materials containing principal organic hazardous constituents (POHCs) have been developed by EPA for use by federal, state, and local agencies or their contractors to assess the accuracy of measurement methods used during RCRA trial burn tests. Audit materials are currently available for 27gaseous organics in five, six, seven, and nine-component mixtures at parts-per-billion levels (7 to 10,000 ppb) in compressed gas cylinders in a balance gas of nitrogen. The criteria used for the selection of 27 gaseous organic compounds is described. Stability studies indicate that all of the organics tested (with the exception of ethylene oxide and propylene oxide below 10 ppb levels) are stable enough to be used as reliable audit materials. Subsequent to completion of the stability studies, 89 performance audits have been conducted with the audit materials to assess the accuracy of the Volatile Organic Sampling Train (VOST) and bag measurement methods during or prior to RCRA trial burn tests. A summary of the audits conducted for each POHC and the measurement system audited is shown in this paper. The audit results obtained with audit gases during RCRA trial burn tests are generally within ±50 percent of the audit concentrations.
The Emergency Planning and Community Right-to-Know law is an exciting new approach to environmental protection. It is based on the belief that the more information citizens have about environmental conditions in their communities, the better equipped they will be to insure their own protection from unacceptable risks to their health and safety. The law requires disclosure by industry of both the presence and release into the environment—including both accidental and “routine” releases—of hazardous substances. The information will be available not only to government regulators, but also to the people most directly affected—the residents of the communities where the substances are located.
The health of populations in industrialised societies has been affected for many years by ambient air pollutants presenting a threat of chronic bronchitis and lung cancer. In the 1980s Indoor pollutants received much needed investigation to assess their hazards to health. Exposure to environmental tobacco smoke and radon is now the subject of much research and concern. This review attempts to put some perspective on lung cancer that is attributable to lifetime exposure to airborne pollutants. The view is expressed that air pollution control authorities have played and are playing a major role in health improvement.
This paper summarizes the presentations given at an APCA International Specialty Conference on tropospheric ozone and ozone control strategies. The conference was held in Hartford, Connecticut on November 16-19, 1987.
This paper describes a laboratory project to assess the accuracy of emission and indoor air quality models to be used in predicting formaldehyde (HCHO) concentrations in residences due to pressed-wood products made with urea-formaldehyde bonding resins. The products tested were partlcleboard underlayment, hardwood- plywood paneling and medium-density fiberboard (mdf). The products were initially characterized in chambers by measuring their formaldehyde surface emission rates over a range of formaldehyde concentrations, air exchange rates and two combinations of temperature and relative humidity (23° C and 5 0% RH; 26°C and 60% RH). They were then installed in a two-room prototype house in three different combinations (underlayment flooring only; underlayment flooring and paneling; and underlayment flooring, paneling, and mdf). The equilibrium formaldehyde concentrations were monitored as a function of air exchange rate. Particleboard underlayment and mdf, but not paneling, behaved as the emission model predicted over a large concentration range, under both sets of temperature and relative humidity. Good agreement was also obtained between measured formaldehyde concentrations and those predicted by a mass-balance indoor air quality model.
Radish plants were exposed three times per week to simulated acidic rain at pH values of 2.6 to 5.4 over the course of four weeks in trials performed at Argonne, Illinois; Ithaca and Upton, New York; Corvallis, Oregon; Oak Ridge, Tennessee; and Toronto, Canada. Uniform genotype, soil media and planting techniques, treatment procedures, biological measurements, and experimental design were employed. Growth of plants differed among trials as a result of variation in greenhouse environmental conditions according to location and facilities. Larger plants underwent greater absolute but lower relative reductions in biomass after exposure to the higher levels of acidity. A generalized Mitscherlich function was used to model the effects of acidity of simulated rain or dry mass of hypocotyls using data from three laboratories that performed duplicate trials. The remaining data, from three other laboratories that performed only one trial each, were used to test the model. When the laboratory by trial effect was removed (influence of different growth. conditions), lack of fit to the Mitscherlich function was insignificant. Thus, a single mathematical model satisfactorily characterized the relationship between acidity and mean plant response. The pH value associated with a 10 percent reduction in mass was 3.3 ± 0.3 for hypocotyls. No value was estimated for shoots because effects oh shoots were not significant. The results of this study demonstrate that a generalized exposure-response model can be developed in the presence of large variations in environmental conditions when plant culture and exposure to simulated rain are standardized among laboratories.
To explore short-term respiratory health risks from acid-polluted fog, 22 normal and 22 asthmatic adult volunteers were exposed in an environmental control chamber to light fogs (∼0.1 g/m3 liquid water content, 10 μm median droplet diameter, 10°C) containing nominally 0, 500, 1000, and 2000 μg/m3 of sulfuric acid. Fog was produced by atomizing dilute acid solution Into purified air humidified to near 100 percent by steam injection. Exposures were administered in random order at 1-week intervals, lasted 1 h, and Included three 10-min periods of moderately heavy exercise. Responses were measured in terms of forced expiratory function, airway resistance, Irritant symptoms, and bronchial reactivity to methacholine aerosol. Sulfuric acid per se showed no more than a slight effect on pulmonary function, even at the highest concentration. Asthmatics experienced bronchoconstrlction, attributable to exercise, under all exposure conditions. Despite the lack of substantial function changes, modest statistically significant Increases in respiratory symptoms occurred with increasing acid concentrations. This unusual response pattern suggests that acid fog effects occur via a mechanism somewhat different from those which govern responses to Irritant gases like SO2 or O3. To the extent these results are relevant to ambient “acid fog” exposures, they predict that no pulmonary dysfunction, and only slight respiratory symptoms if any, are likely to occur.
As part of research carried out on the transformations of pollutants In coal-fired power plant plumes, we have developed and tested SO2, NO X , and O3 analyzers with a short response time of about 4 seconds. These analyzers, tested In the laboratory and on board an aircraft In plumes, exhibit good linearity of response as well as acceptable background noise. The background noise can be further reduced by appropriate signal processing. These short response time analyzers provide a valuable tool for plume studies, allowing a precise mapping of polluted areas and of the corresponding sources
