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61.
George T. Wolff Patricia E. Korsog 《Journal of the Air & Waste Management Association (1995)》2013,63(9):1173-1177
The 1990 Clean Air Act Amendments require states with O3 nonattainment areas to adopt regulations to enforce reasonable available control technologies (RACT) for NOX stationary sources by November 1992. However, if the states can demonstrate that such measures will have an adverse effect on air quality, NOX requirements may be waived. To assist the states in making this decision, the U.S. EPA is attempting to develop guidelines for the states to use in deciding whether NOX reductions will have a positive or negative impact on O3 air quality. Although NOX is a precursor of O3, at low VOC/NOX ratios, the reduction of NOX can result in increased peak O3. EPA is examining existing information on VOC/NOX ratios to develop “rules of thumb” to guide the states in their decision-making process. An examination of 6 a.m. to 9 a.m. VOC/NOX ratios at a number of sites in the eastern U.S. indicates that the ratio is highly variable from day-to-day and there is no apparent relationship between ratios measured at different sites within the same area. In addition, statistical analysis failed to identify significant relationships between the 6 a.m. to 9 a.m. VOC/NOX ratio and the maximum 1-hr. O3 within a given area. Since we know from smog chamber and modeling studies that such a relationship exists, this further invalidates the assumption that a ratio measured at a single site is representative of the ratio for the entire region. Based on this Information, we conclude that having the 6 a.m. to 9 a.m. ambient VOC/NOX ratio for a given area is insufficient information, by itself, to decide whether a VOC-alone, a NOx-alone, or a combined VOC-NOX reduction strategy is a viable or optimum O3-reduction strategy. 相似文献
62.
George R. Hendrey Keith F. Lewin Zbigniew Kolber Lance S. Evans 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1324-1327
A prototype Free-Air Controlled Enrichment (FACE) system was developed at Brookhaven National "Laboratory (BNL) for the experimental control of gas concentrations in an open field, without any form of enclosure. This FACE system consists of a toroidal plenum chamber, 15 m in diameter, with a series of 32 vertical vent pipes from which the release of a test gas can be controlled. Data on gas concentration at the center of the array and wind velocity are fed to a microprocessor where a proportional, integrative, differential (PID) algorithm is used to regulate a mass-flow controller. Data on wind direction are used to control the opening and closing of the vertical vent pipes to maintain an upwind release. In 72 hours of continuous operation during which wind velocity varied between 0.3 to 8 m sec-1, the FACE prototype maintained 1 -min averaged concentrations within twenty percent of the 40 ppb set point 94 percent of the time. 相似文献
63.
Peter A. Scheff Donna M. Kenski Joseph Chung George Wolff 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1048-1057
Abstract Large-scale studies like the Southeast Michigan Ozone Study (SEMOS) have focused attention on quantifying and spedating inventories for volatile organic compounds (VOCs). One approach for evaluating the accuracy of a VOC emission inventory is the development of a chemical mass balance (CMB) receptor model for ambient non-methane organic compound (NMOC) measurements. CMB evaluations of ambient hydrocarbon data provide a sample-specific allocation of emissions to individual source categories. This study summarizes the results of an application of the CMB model to the NMOC data from the SEMOS study. Comparison of CMB results with emission inventory values for the Detroit area show that vehicle emissions are well represented by the inventory, as are architectural coatings and coke ovens. Estimated emissions from petroleum refineries and graphic arts industries are much lower in the inventory than determined from the receptor allocation. Under-reporting of fugitive VOC emissions from petroleum refineries is an ongoing problem. Emissions from graphic arts industries are underestimated in the inventory partly because of the broad characterization of the emission factor (i.e., mass emitted/capita), which may be less useful when specific locations and days are under consideration. This study also demonstrates the effectiveness of the CMB approach when used prospectively to track the implementation of emission control strategies. While vehicle emission concentrations were unchanged from 1988 to 1993, measurement-based CMB results suggest a decrease in evaporative emissions during this time period resulting from Reid vapor pressure (RVP) reductions (from 11.0 psi in 1988 to 8.6 psi in 1993) and fleet turnover. Changes in emissions from coke plants and petroleum refineries were also seen in the CMB allocations for these sources. 相似文献
64.
Peter Babich Mark Davey George Allen Petros Koutrakis 《Journal of the Air & Waste Management Association (1995)》2013,63(7):1095-1105
ABSTRACT Methods that measure PM25 mass, total particulate NO3 -, and elemental carbon (EC) were evaluated in seven U.S. cities from 1997 to 1999. Sampling was performed in Bakersfield, CA; Boston, MA; Chicago, IL; Dallas, TX; Philadelphia, PA; Phoenix, AZ; and Riverside, CA. Evaluating and validating methods that measure the components of fine mass are important to the effort of establishing a speciation-monitoring network. The Harvard Impactor (HI), which measures fine particle mass, showed excellent agreement (r2 = 0.99) with the PM25 Federal Reference Method (FRM) for 81 24-hr samples in Riverside and Bakersfield. The HI also showed good precision (4.8%) for 243 24-hr collocated samples over eight studies. The Aethalometer was employed in six of the sampling locations to measure black carbon (BC). These values were compared to EC as measured from a quartz filter using thermal analysis. For the six cities combined, the two methods were highly correlated (r2 = 0.94; 187 24-hr samples); however, the BC values were approximately 24% less than the EC measurements consistently across all six cites. This compares well to results observed for EC/BC measurements observed in other semi-urban areas. Par-ticulate NO3 - was measured using the Harvard-EPA Annular Denuder System (HEADS). This was compared to the NO3 - measured from the HI Teflon (DuPont) filter to assess NO3 - artifacts. Significant NO3 - losses (approximately 50% of total NO3 -) were found in Riverside, Philadelphia, and Boston, while minimal artifacts were observed in the other sites. Two types of HEADS configurations were employed in five cities. One system used a Na2CO3-coated glass fiber filter, and the other type used a nylon filter to collect volatilized NO3 - from the Teflon filter. The HEADS with the Na2CO3-coated filter consistently underestimated the total particulate NO3 - by approximately 20% compared to the nylon HEADS. 相似文献
65.
Li-Te Chang Helen H. Suh Jack M. Wolfson Kshipra Misra George A. Allen Paul J. Catalano 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1414-1422
ABSTRACT While researchers have linked acute (less than 12-hr) ambient O3, PM25, and CO concentrations to a variety of adverse health effects, few studies have characterized short-term exposures to these air pollutants, in part due to the lack of sensitive, accurate, and precise sampling technologies. In this paper, we present results from the laboratory and field evaluation of several new (or modified) samplers used in the “roll-around” system (RAS), which was developed to measure 1-hr O3, PM25, and CO exposures simultaneously. All the field evaluation data were collected during two sampling seasons: the summer of 1998 and the winter of 1999. To measure 1-hr O3 exposures, a new active O3 sampler was developed that uses two nitrite-coated filters to measure O3 concentrations. Laboratory chamber tests found that the active O3 sampler performed extremely well, with a collection efficiency of 0.96 that did not vary with temperature or relative humidity (RH). In field collocation comparisons with a reference UV photometric monitor, the active O3 sampler had an effective collection efficiency ranging between 0.92 and 0.96 and a precision for 1-hr measurements ranging between 4 and 6 parts per billion (ppb). The limits of detection (LOD) of this method were 9 ppb-hr for the chamber tests and ~16 ppb-hr for the field comparison tests. PM2.5 and CO concentrations were measured using modified continuous monitors—the DustTrak and the Langan, respectively. A size-selective inlet and a Nafion dryer were placed upstream of the DustTrak inlet to remove particles with aerodynamic diameters greater than 2.5 um and to dry particles prior to the measurements, respectively. During the field validation tests, the DustTrak consistently reported higher PM2.5 concentrations than those obtained by the collocated 12-hr PM2 5 PEM samples, by approximately a factor of 2. After the DustTrak response was corrected (correction factor of 2.07 in the summer and 2.02 in the winter), measurements obtained using these methods agreed well with R2 values of 0.87 in the summer and 0.81 in the winter. The results showed that the DustTrak can be used along with integrated measurements to measure the temporal and spatial variation in PM2 5 exposures. Finally, during the field validation tests, CO concentrations measured using the Langan were strongly correlated with those obtained using the reference method when the CO levels were above the LOD of the instrument [~1 part per million (ppm)]. 相似文献
66.
Jon M. Heuss Dennis F. Kahlbaum George T. Wolff 《Journal of the Air & Waste Management Association (1995)》2013,63(7):772-788
Abstract A national analysis of weekday/weekend ozone (O3) differences demonstrates significant variation across the country. Weekend 1-hr or 8-hr maximum O3 varies from 15% lower than weekday levels to 30% higher. The weekend O3 increases are primarily found in and around large coastal cities in California and large cities in the Midwest and Northeast Corridor. Both the average and the 95th percentile of the daily 1-hr and 8-hr maxima exhibit the same general pattern. Many sites that have elevated O3 also have higher O3 on weekends even though traffic and O3 precursor levels are substantially reduced on weekends. Detailed studies of this phenomenon indicate that the primary cause of the higher O3 on weekends is the reduction in oxides of nitrogen (NOx) emissions on weekends in a volatile organic compound (VOC)-limited chemical regime. In contrast, the lower O3 on weekends in other locations is probably a result of NOx reductions in a NOx-limited regime. The NOx reduction explanation is supported by a wide range of ambient analyses and several photochemical modeling studies. Changes in the timing and location of emissions and meteorological factors play smaller roles in weekend O3 behavior. Weekday/weekend temperature differences do not explain the weekend effect but may modify it. 相似文献
67.
Verne L. Rhodes George Kriek Nelson Lazear Jean Kasakevich Marie Martinko R.P. Heggs 《Journal of the Air & Waste Management Association (1995)》2013,63(7):781-788
Abstract Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 °C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations. 相似文献
68.
Terer T Muasya AM Dahdouh-Guebas F Ndiritu GG Triest L 《Journal of environmental management》2012,93(1):71-84
The current study documented local utilization of Cyperus papyrus L. (papyrus), harvesting patterns, threats, and local management practices among the Endorois community living around Loboi swamp (Kenya). Papyrus is a highly productive freshwater macrophyte that is widely utilized throughout tropical Africa. However, increased human population and poverty, has led to over exploitation and conversion of papyrus wetlands to agricultural fields. Nonetheless, users of papyrus hold important local ecological knowledge (LEK) and practices. We show that Endorois practices on papyrus uses are compatible with the management priorities of the swamp and a wider conservation framework using data obtained from three focus group discussions (FGD), interviews of 34 households and 15 key informants. The study revealed that papyrus support local livelihood notably as a source of income (papyrus mats are sold), cattle fodder, roofing materials (shelter), and cooking fuel. The study further revealed important LEK relating to harvesting patterns, recovery after harvesting and traditional management practices. Correlation and principal component analyses showed that experienced old harvesters (EXPERT) avoided harvesting repeatedly at the same location (REVISIT), thereby allowing recovery of papyrus when compared to younger harvesters (r = 0.63, p < 0.01). However, over 70% of harvesters predicted a decrease in papyrus coverage in the future due to the current diversion of water from the swamp, and frequent droughts, despite the instituted traditional management strategies (e.g. rotational harvesting) to curb overharvesting. The study concluded that the documentation of site-scale papyrus users' profile, LEK, and traditional practices are vital for the conservation and management of Loboi swamp. 相似文献
69.
Niazi NK Singh B Van Zwieten L Kachenko AG 《Environmental science and pollution research international》2012,19(8):3506-3515
This field study investigated the phytoremediation potential of two arsenic (As) hyperaccumulating fern species, Pityrogramma calomelanos var. austroamericana and Pteris vittata over 27-month duration at a disused As-contaminated cattle-dip site located at Wollongbar, NSW, Australia. Ferns planted in January 2009 were harvested following 10, 22 and 27 months of growth. A detailed soil sampling was undertaken in June 2009 (initial, n?=?42 per plot) and limited sampling in April 2011 (after 27 months, n?=?15 per plot) to measure total and phosphate-extractable As concentrations in soil at 0?-?20-, 20?-?40- and 40?-?60-cm depths. The choice of the limited number of samples was considered sufficient to estimate the changes in soil As concentration following phytoremediation based on a geostatistical model. The average frond dry biomass, As concentration and As uptake were significantly (P?0.001?-?0.05) greater in P. calomelanos var. austroamericana than P. vittata, at all three harvests (1.6?-?4.3, 1.3?-?1.5 and 2.2?-?5.7 times, respectively). After 27-months of growth, P. calomelanos var. austroamericana removed 8,053 mg As (i.e. cumulative over three harvests) in plot B (25.4 kg As ha(-1)) that was 2.65 times higher than that depleted by P. vittata (3,042 mg As in plot A (9.7 kg As ha(-1))). The cumulative frond As uptake data of the two fern species revealed that P. calomelanos var. austroamericana extracted 1.7?-?3.9 % and P. vittata removed 0.53?-?1.5 % of total As from soil at three depths. However, for the surface (0?-?20 cm) and subsurface (40?-?60 cm) layers, the (post-experiment) soil As data indicated that total As concentration in soil was reduced by 49 and 63 % (P?0.05), respectively, using P. calomelanos var. austroamericana; and 17 and 15 % (P?>?0.05), respectively, by P. vittata. Our results show that phytoremediation time based on observed changes in soil As based on limited sampling is not reliable; hence, it is recommended that the frond As uptake should be considered in order to evaluate the phytoremediation efficiency of the two fern species at the experimental site. Using As uptake of the two fern species, we estimate that with P. calomelanos var. austroamericana it would take 55?-?125 years to decrease mean total As content below the ecological investigation level (20 mg kg(-1)) in the surface and subsurface soils, whereas with P. vittata 143?-?412 years would be required to achieve this target. 相似文献
70.
Optimum conditions for microbial carbonate precipitation 总被引:3,自引:0,他引:3
The type of bacteria, bacterial cell concentration, initial urea concentration, reaction temperature, the initial Ca(2+) concentration, ionic strength, and the pH of the media are some factors that control the activity of the urease enzyme, and may have a significant impact on microbial carbonate precipitation (MCP). Factorial experiments were designed based on these factors to determine the optimum conditions that take into consideration economic advantage while at the same time giving quality results. Sporosarcina pasteurii strain ATCC 11859 was used at constant temperature (25°C) and ionic strength with varying amounts of urea, Ca(2+), and bacterial cell concentration. The results indicate that the rate of ureolysis (k(urea)) increases with bacterial cell concentration, and the bacterial cell concentration had a greater influence on k(urea) than initial urea concentration. At 25 mM Ca(2+) concentration, increasing bacterial cell concentration from 10(6) to 10(8)cells mL?1 increased the CaCO(3) precipitated and CO(2) sequestrated by over 30%. However, when the Ca(2+) concentration was increased 10-fold to 250 mM Ca(2+), the amount of CaCO(3) precipitated and CO(2) sequestrated increased by over 100% irrespective of initial urea concentration. Consequently, the optimum conditions for MCP under our experimental conditions were 666 mM urea and 250 mM Ca(2+) at 2.3×10? cells mL?1 bacterial cell concentration. However, a greater CaCO(3) deposition is achievable with higher concentrations of urea, Ca(2+), and bacterial cells so long as the respective quantities are within their economic advantage. X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray analyzes confirmed that the precipitate formed was CaCO(3) and composed of predominantly calcite crystals with little vaterite crystals. 相似文献