Air & waste : journal of the Air & Waste Management Association最新文献

Many state and federal agencies have prepared risk assessment guidelines, which describe methods for quantifying health risks associated with exposure to vapors and particulates emitted from point and area sources (e.g., California Air Pollution Control Officers Association [CAPCOA] under the Air Toxics "Hot Spots" Act [Assembly Bill 2588] and the U.S. Environmental Protection Agency [EPA] under the Clean Air Act). In general, these guidelines recommend or require the use of upperbound "point" estimates for numerous exposure parameters. This methodology yields a single risk estimate, which is intended not to underestimate the true risk and may significantly overstate it. This paper describes a risk assessment of a facility's airborne emissions using a probabilistic approach, which presents a range and distribution of risk estimates rather than a single point estimate. The health risks to residents living near a food processing facility, as estimated using techniques recommended by California AB2588, are compared to the results of a probabilistic analysis. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were identified as the emitted chemicals of concern. The point estimate method recommended by CAPCOA resulted in estimates that were greater than the 99.99th percentile risk predicted by the probabilistic analysis. As shown in other assessments of persistent airborne chemicals, secondary or indirect exposure pathways (i.e., ingestion of beef, ingestion of cow's milk, and ingestion of mother's milk) rather than inhalation, were the greatest contributors to risk. In this analysis, the probability distributions for the cancer potency factor and ingestion of cow's milk had the largest impact on the results of the 33 exposure factors considered.

To put waste-to-energy (WTE) in perspective, it is important to see how it measures up environmentally to other power generation utility sources. This paper compares actual WTE facility emissions with those from fossil fuel combustion utility sources. This comparison is made on an electricity production basis, such as a pound of pollutant per megawatt-hour of net electricity generated, for each ower generation source.

A new methodolgy based on a generic pollution balance equation, has been developed for minimizing waste production in manufacturing processes. A "pollution index," defined as the mass of waste produced per unit mass of a product, has been introduced to provide a quantitative measure of waste generation in a process. A waste reduction algorithm also has been developed from the pollution balance equation. This paper explains this methodology and demonstrates the applicability of the method by a case study.

Nitrous oxide (N2O) is a trace gas contributing to stratospheric ozone depletion and global warming. Although a large quantity of information exists about N2O emissions from various ecosystems, this study was initiated to demonstrate the features of N2O emissions from sea-based waste disposal sites in Osaka City in relation to CH4 emissions. Average N2O emissions at an active landfill (S-Site) were several times higher than those at a closed landfill (N-Site). Average CH4 emissions were also much greater at the S-Site. Regarding the nature of N2O emissions, remarkable emissions often were observed with aerobic waste layers at the N-Site, suggesting almost inversely related N2O emissions with CH4 production at the N-Site. However, at the S-Site a few exceptionally high N2O emissions were noted in cases of high CH4 emissions.

The kinetics of H2S oxidation in a biofilter were evaluated and the reaction rates determined to be first-order at low concentrations (< 200 ppm), zero-order at high concentrations (> 400 ppm), and fractional-order in the intermediate concentration range for H2S in the inlet waste gas. The overall performance of the biofilter system and changes in compost properties were investigated for 200 days of operation. The compost biofilter showed good buffering capacities to variations in gas flow rate and pollutant (H2S) loading impacts. Hydrogen sulfide removal efficiencies exceeding 99.9% were consistently observed. System acidification and sulfate accumulation were identified as inhibitors of required biological activity. Routine washing of the compost effectively mitigated these deficiencies. System upset was determined to be caused by compost dry-out or system overloading. Methods were developed to provide for recovery of contaminated filter material.

In June 1991, General Motors Research and Development Center (GMR&D) participated in a remote sensing study conducted by the California Air Resources Board and the U.S. Environmental Protection Agency. During this study, the GMR&D remote sensor was used to measure the carbon monoxide (CO) and hydrocarbon (HC) emissions from approximately 15,000 vehicles. The vehicle type (passenger car, light-duty truck, or medium/heavy-duty truck), manufacturer, and model year were identified for each vehicle by acquiring registration data from the state of California. Analyses were performed separately for each vehicle type and for passenger cars by separate model years. The data indicate that the passenger cars with the highest 10% of CO emissions generated approximately 58% of the total CO from all cars. Similarly, the 10% highest HC-emitting cars generated 65% of the total HC from cars. It was found that for each model year of vehicle, the distribution of emission concentrations followed a logarithmic relationship. The logarithmic functions that describe these relationships can be used to estimate the fraction of vehicles that emitted at or above any given concentration of CO or HC. However, these logarithmic functions only describe measured distributions for vehicles emitting more than 1% CO and 0.015% HC.

A recycling exposure system, which has characteristics of dynamic and static systems, has been designed and constructed for calibrating passive sampling tubes. This system is very easy to set up and maintain. Organic vapors inside the system are generated by syringe injection, and homogeneous vapors are circulated by a metal-bellows pump. The concentrations of light hydrocarbons (e.g., isoprene) may decrease slightly after circulating for longer than 10 hours; however, this system is very stable for C5-C8 hydrocarbons for at least eight hours. The system has been used successfully to calibrate Perkin-Elmer diffusion tubes packed with Chromosorb 106 for collecting benzene vapor at low exposure doses (< 70 ppmv x min). The entire system can be easily and effectively cleaned by circulating through a U-tube packed with activated carbon.

A study was performed to determine the source of low concentrations of volatile organic compounds (VOCs) detected in groundwater samples at a solid waste management facility. The affected wells were identified as hydraulically upgradient of an old unlined facility, but downgradient of a new clay-lined landfill. These monitoring wells are close to both sites. Subsurface landfill gas migration was identified after a low permeability cap was installed on the older site. Subsurface gas pressure was monitored to identify horizontal landfill gas migration. Monitoring well headspace gases were evaluated to identify depressed oxygen concentrations and methane because of landfill gas migration into the well. Monitoring well headspace gas VOC concentrations were compared to groundwater VOC concentrations to determine the direction of phase transfer. A ratio above 1.0 of the observed well headspace gas concentration of a VOC to the concentration that would be in equilibrium with the groundwater concentration indicates gas-to-water phase transfer within the well. For the major gas-phase and aqueous-phase VOC, cis-1,2-dichloroethene, gas-to-water phase transfer is clearly indicated from the data for two of the four wells. Fifteen other VOCs were detected in monitoring well headspace gases but not in groundwater samples from the four wells studied. Only one compound in one well was detected in the groundwater sample but not in the headspace gases, and only one compound in one well was detected in both matrices at concentrations that suggested water-to-gas phase transfer. This study suggests that if landfill gas is suspected as the source of detected VOCs, monitoring well construction and stratigraphy are important considerations when attempting to differentiate between groundwater contamination by landfill gas and contamination from other sources.

Ozone (O3) is suspected of being the most significant air pollutant affecting vegetation in the United States. Ozone concentrations measured at Bearden Knob and Parsons, located in a remote forested region of northcentral West Virginia, were characterized and compared with exposures experienced at other sites in the region. From 1988 to 1992, 1988 was one of the highest O3 exposure years in the region, while 1992 was the lowest. At almost all sites in 1992, few hourly average concentrations were > or = 0.10 ppm, while in 1988 several sites had more than 100 hourly average concentrations > or = 0.10 ppm. These instances occurred at both high- and low-elevation sites. In 1992, the high-elevation Bearden Knob site experienced a flat-type diurnal pattern, while the nearby low-elevation Parsons site experienced a changing diurnal pattern, indicative of scavenging. Using several indices, O3 exposures at Parsons were less than those at Bearden Knob. Evaluation of hourly averaged data for all sites in the region from 1988 to 1992 showed that Horton Station experienced the highest W126 O3 exposures. Horton Station is a high-elevation site in the mountains of southwestern Virginia. Square-wave exposures have been used under artificial conditions in vegetation experiments. If square-wave exposures are observed under ambient conditions, then the vegetation data collected under artificial conditions may be relevant for predictive purposes. Square-wave exposures were characterized for two high-elevation sites. In 1992, Horton Station experienced 25 episodes for which the hourly average concentrations remained near 0.05 ppm for eight hours or longer; there were 18 episodes for which the hourly average concentrations remained near 0.06 ppm, and three episodes for which the concentrations remained near 0.07 ppm. Bearden Knob experienced 31 episodes of eight hours or longer for hourly average concentrations near 0.05 ppm, 13 episodes at or near 0.06 ppm, and three episodes at or near 0.07 ppm. Until experiments are performed to determine the relative importance of hourly average concentrations above 0.03 ppm for assessing vegetation effects, using single-parameter exposure indices to predict effects may produce inconsistent results.