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991.
Thomas M. Baines Joseph H. Somers Craig A. Harvey 《Journal of the Air & Waste Management Association (1995)》2013,63(6):616-621
For the past several years, EPA has been measuring particulate emissions from a variety of heavy-duty diesel engines through contracts with Southwest Research Institute. Particulate emissions samples have been collected using an exhaust splitter to divert a fraction of the engine exhaust into a standard dilution tunnel. A small fraction of the diluted exhaust from the tunnel is pulled through a filter from which particulate mass and, in some cases, organic content of the particulate is determined. This paper discusses the sampling system and gives particulate emission factors that have been computed from truck and bus fuel consumption data as well as average truck and bus speed data from New York and Los Angeles (freeway and nonfreeway usage). Average particulate emission test results (steady state tests) for 2-stroke engines were 4.74 g/kg fuel and for 4-stroke engines were 2.64 g/kg fuel. Using average particulate emissions results, a particulate emission factor range of 0.8 to 1.3 g/km was computed. Nationwide diesel particulate emissions were calculated to be 88,000 metric tons per year. 相似文献
992.
M. Mansi V. Romano F. Senatore 《Journal of the Air & Waste Management Association (1995)》2013,63(8):881-882
ABSTRACT In this paper, assumptions regarding future land use as a key uncertainty is considered and its impact on risk analysis for contaminated sites is assessed. Risks are assessed for two land use scenarios (current-use industrial and future-use residential) using probabilistic models that incorporate uncertainty and variability in the exposure parameters. Residual risks are calculated for both industrial and residential cleanup standards. A Superfund site in northern California is considered. In general, for the unremediated case, the future-use residential scenarios produce larger risks (1 to 3 orders of magnitude) than current- (continued) use industrial scenarios. For the Superfund site studied, the residual risks calculated for the remedy selected was not sufficiently protective of future-use residents in that it did not meet .S. Environmental Protection Agency (EPA) risk goals, but was protective of current-use workers, even though the cleanup criteria were based on residential use. Alternative risk management practices, such as deed restrictions, can be used in such cases. 相似文献
993.
994.
Bernd R. T. Simoneit M. A. Mazurek T. A. Cahill 《Journal of the Air & Waste Management Association (1995)》2013,63(4):387-390
The atmosphere of the Lake Tahoe air basin is contaminated with high molecular weight (> C12) petroleum hydrocarbons. Aerosol samples were collected by high-volume filtration and the solvent-soluble organic matter was analyzed. The relative concentrations of petroleum residues found were as follows: winter > summer and day > night. This contamination is primarily due to the poorer combustion of diesel and home heating fuels at that altitude and during periods of colder climate. 相似文献
995.
Howard M. Ellis Peter C. Liu Charles Runyon 《Journal of the Air & Waste Management Association (1995)》2013,63(6):670-675
The purpose of this study was to evaluate alternative prediction models for the SO2 concentrations produced in the vicinity of the Ohio Edison Company Sammis Power Plant. The plant is situated in the northeastern portion of the Ohio River Valley in complex terrain. Comparisons of the 16 highest predicted and measured short-term SO2 concentrations were conducted for a one year period for 58 alternative models. Several models were found to predict reasonably accurately the 16 highest measured 24-hour SO2 concentrations. Each of these models requires an upward adjustment in the plume centerline location as the plume is transported downwind in rising terrain. These same models overpredict by substantial margins the 16 highest measured 3-hour SO2 concentrations. Improvements in emissions inventory data and improvements in the prediction models used are believed necessary to increase prediction accuracy further. 相似文献
996.
997.
998.
S. Witz M. Smith M. Shu A. B. Moore 《Journal of the Air & Waste Management Association (1995)》2013,63(3):276-278
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. 相似文献
999.
M. J. Cooke R. A. Wadden 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1197-1199
Abstract Confidence interval construction for central tendency is a problem of practical consequence for those who must analyze air contaminant data. Determination of compliance with relevant ambient air quality criteria and assessment of associated health risks depend upon quantifying the uncertainty of estimated mean pollutant concentrations. The bootstrap is a resampling technique that has been steadily gaining popularity and acceptance during the past several years. A potentially powerful application of the bootstrap is the construction of confidence intervals for any parameter of any underlying distribution. Properties of bootstrap confidence intervals were determined for samples generated from lognormal, gamma, and Weibull distributions. Bootstrap t intervals, while having smaller coverage errors than Student's t or other bootstrap methods, under-cover for small samples from skewed distributions. Therefore, we caution against using the bootstrap to construct confidence intervals for the mean without first considering the effects of sample size and skew. When sample sizes are small, one might consider using the median as an estimate of central tendency. Confidence intervals for the median are easy to construct and do not under-cover. Data collected by the Northeast States for Coordinated Air Use Management (NESCAUM) are used to illustrate application of the methods discussed. 相似文献
1000.
Dennis Schuetzle Joseph M. Perez 《Journal of the Air & Waste Management Association (1995)》2013,63(8):751-755
The potential problem of 1-nitropyrene (1-NP) formation during filter sampling of diesel emissions from dilution tubes is assessed. Rates of formation are calculated using data generated from several independent filter exposure studies. A portion of the 1-NP (12% average) found in participates collected from light-duty (LDD) and heavy-duty diesels (HOD) was found to be due to formation on the filter under average sampling conditions of 10-15/1 dilution at 44°C with 3 ppm NO2 for 23 min. On the average, the concentration of 1-NP in participates emitted from HDD is 16 times less than that found in LDD run under similiar transient conditions. The average emission rate of 1-NP generated from the LDD and HDD was 4.7 μg/km and 1.5 μg/km, respectively for the vehicles operating under Federal Test Procedure (FTP)-transient conditions. Under operating conditions which increase exhaust temperature (increased speed and load), the concentration of nitro-PAH is significantly reduced with a concurrent increase in the concentration of partially oxidized nitro-PAH and dinitro-PAH. The concentration of 1-NP in the particulates measured from HDD in these dilution tube studies (0.33-0.95 ppm, depending upon engine load) is comparable to that measured in highway tunnel experiments (0.54 ppm average). 相似文献