Variance Design and Air Pollution Control

Confronted with shortages of low sulfur content residual fuel oil and, consequently, faced with the threat of social and economic upheaval, several air pollution control authorities in the Northeastern states were forced to relax hard-won air quality standards during the winter of 1972. The authorities did so by granting variances to their sulfur content standards for residual fuel oil. This paper examines the institutional characteristics of these variance policies from an economic incentive standpoint. After setting up desirable structural criteria for institutional design of such crisis policies, the authors examine the experience of the winter of 1972 and arrive at policy guidelines which recommend themselves for consideration in future periods of fuel oil shortages.     

Infrared Photography as an Air Pollution Surveillance Instrument

Remote sensing is an extremely new science which developed from World War II technology. At that time, infrared sensitive film (false color) was used to detect such things as troop movements and camouflaged war materials. In essence, the film displayed a color contrast between the artificial and organic vegetation.     

一种改进的多学习教与学优化算法

针对传统教与学算法在解决复杂多峰函数优化问题时,具有局部最优且搜索开发能力较差的缺点,提出了一种改进的多学习教与学优化算法,新算法为学员的每一维加入不同的教学因子,设计了基于学员均值比较的教师选择策略和向教师及学员学习的多学习策略。基于多个单峰和多峰函数的仿真结果表明,新算法跟传统的、改进的教与学算法相比,在稳定性、寻优精度和收敛速度方面更具优势。     

Salinity modulates biochemical and histopathological changes caused by silver nanoparticles in juvenile Persian sturgeon (Acipenser persicus)

Environmental Science and Pollution Research - The objective of this study was to evaluate the effect of salinity on the acute and sub-chronic toxicity of silver nanoparticles (AgNPs) in Persian...     

Fast response measurements of the dispersion of nanoparticles in a vehicle wake and a street canyon

The distributions of nanoparticles (below 300 nm in diameter) change rapidly after emission from the tail pipe of a moving vehicle due to the influence of transformation processes. Information on this time scale is important for modelling of nanoparticle dispersion but is unknown because the sampling frequencies of available instruments are unable to capture these rapid processes. In this study, a fast response differential mobility spectrometer (Cambustion Instruments DMS500), originally designed to measure particle number distributions (PNDs) and concentrations in engine exhaust emissions, was deployed to measure particles in the 5–1000 nm size range at a sampling frequency of 10 Hz. This article presents results of two separate studies; one, measurements along the roadside in a Cambridge (UK) street canyon and, two, measurements at a fixed position (20 cm above road level), centrally, in the wake of a single moving diesel-engined car. The aims of the first measurements were to test the suitability and recommend optimum operating conditions of the DMS500 for ambient measurements. The aim of the second study was to investigate the time scale over which competing influences of dilution and transformation processes (nucleation, condensation and coagulation) affect the PNDs in the wake of a moving car. Results suggested that the effect of transformation processes was nearly complete within about 1 s after emission due to rapid dilution in the vehicle wake. Furthermore, roadside measurements in a street canyon showed that the time for traffic emissions to reach the roadside in calm wind conditions was about 45 ± 6 s. These observations suggest the hypothesis that the effects of transformation processes are generally complete by the time particles are observed at roadside and the total particle numbers can then be assumed as conserved. A corollary of this hypothesis is that complex transformation processes can be ignored when modelling the behaviour of nanoparticles in street canyons once the very near-exhaust processes are complete.     

Development of a microscale emission factor model for particulate matter for predicting real-time motor vehicle emissions

The U.S. Environmental Protection Agency's National Exposure Research Laboratory is pursuing a project to improve the methodology for modeling human exposure to motor vehicle emissions. The overall project goal is to develop improved methods for modeling the source through the air pathway to human exposure in significant exposure microenvironments. Current particulate matter (PM) emission models, particle emission factor model (used in the United States, except California) and motor vehicle emission factor model (used in California only), are suitable only for county-scale modeling and emission inventories. There is a need to develop a site-specific real-time emission factor model for PM emissions to support human exposure studies near roadways. A microscale emission factor model for predicting site-specific real-time motor vehicle PM (MicroFacPM) emissions for total suspended PM, PM less than 10 microm aerodynamic diameter, and PM less than 2.5 microm aerodynamic diameter has been developed. The algorithm used to calculate emission factors in MicroFacPM is disaggregated, and emission factors are calculated from a real-time fleet, rather than from a fleet-wide average estimated by a vehicle-miles-traveled weighting of the emission factors for different vehicle classes. MicroFacPM requires input information necessary to characterize the site-specific real-time fleet being modeled. Other variables required include average vehicle speed, time and day of the year, ambient temperature, and relative humidity.     

Laboratory and field evaluation of crystallized DOW 704 oil on the performance of the Well Impactor Ninety-Six fFine particulate matter fractionator

Subsequent to the 1997 promulgation of the Federal Reference Method (FRM) for monitoring fine particulate matter (PM2.5) in ambient air, U.S. Environmental Protection Agency (EPA) received reports that the DOW 704 diffusion oil used in the method's Well Impactor Ninety-Six (WINS) fractionator would occasionally crystallize during field use, particularly under wintertime conditions. Although the frequency of occurrence on a nationwide basis was low, uncertainties existed as to whether crystallization of the DOW 704 oil may adversely affect a sampling event's data quality. In response to these concerns, EPA and the State of Connecticut Department of Environmental Protection jointly conducted a series of specialized tests to determine whether crystallized oil adversely affected the performance of the WINS fractionator. In the laboratory, an experimental setup used dry ice to artificially induce crystallization of the diffusion oil under controlled conditions. Using primary polystyrene latex calibration aerosols, standard size-selective performance tests of the WINS fractionator showed that neither the position nor the shape of the WINS particle size fractionation curve was substantially influenced by the crystallization of the DOW 704 oil. No large particle bounce from the crystallized impaction surface was observed. During wintertime field tests, crystallization of the DOW 704 oil did not adversely affect measured PM2.5 concentrations. Regression of measurements with crystallized DOW 704 versus liquid dioctyl sebacate (DOS) oil produced slope, intercept, and R2 values of 0.98, 0.1, and 0.997 microg/m3, respectively. Additional field tests validated the use of DOS as an effective impaction substrate. As a result of these laboratory and field tests, DOS oil has been approved by EPA as a substitute for DOW 704 oil. Since the field deployment of DOS oil in 2001, users of this alternative oil have not reported any operational problems associated with its use in the PM2.5 FRM. Limited field evaluation of the BGI very sharp cut cyclone indicates that it provides a viable alternative to the WINS fractionator.     

Agricultural opportunities to mitigate greenhouse gas emissions

Agriculture is a source for three primary greenhouse gases (GHGs): CO(2), CH(4), and N(2)O. It can also be a sink for CO(2) through C sequestration into biomass products and soil organic matter. We summarized the literature on GHG emissions and C sequestration, providing a perspective on how agriculture can reduce its GHG burden and how it can help to mitigate GHG emissions through conservation measures. Impacts of agricultural practices and systems on GHG emission are reviewed and potential trade-offs among potential mitigation options are discussed. Conservation practices that help prevent soil erosion, may also sequester soil C and enhance CH(4) consumption. Managing N to match crop needs can reduce N(2)O emission and avoid adverse impacts on water quality. Manipulating animal diet and manure management can reduce CH(4) and N(2)O emission from animal agriculture. All segments of agriculture have management options that can reduce agriculture's environmental footprint.     

Some issues relating to the use of perfluorooctanesulfonate (PFOS) samples as reference standards

Samples of potassium perfluorooctanesulfonate (PFOSK) from three suppliers were analyzed by LC-ESI-MS/MS for purity and by LC-ESI-MS for the percentage of linear isomer present. Our data indicated that the purity ranged from 80% to 98% and the percentages of linear isomer from 67% to 79%. The proportion of branched isomers present in the samples was also estimated using (19)F NMR. These results agreed quite closely with those found by LC-ESI-MS indicating that there is essentially no difference in overall SIM response factor for the branched isomers vs. that of the linear isomer. Several further observations relevant to the use of standards when analyzing for PFOS were encountered during this study. It appears unlikely that matrix effects attributable to the cation (sodium or potassium) present in PFOSNa or PFOSK internal standards is an issue. In seeking potential matrix effects, it was found that the chromatography was improved substantially when the standard was injected as a solution in 80:20 methanol/water rather than 100% methanol. Notably, in concert with the improvement in chromatography, an increase of about 10% in response was observed. In some closely related studies, when (18)O(2) mass-labeled perfluorohexanesulfonate was used as an internal standard, the actual and theoretical concentration ratios matched closely those for related native sulfonates as long as they did not co-elute. However, when they did co-elute, the peak intensities of the native species were enhanced by about 5%, while those of the labeled compound were suppressed by a similar amount. If this effect were not taken into account, the concentration of the native would be inflated by 10%.