A quantitative description of vehicle exhaust particle size distributions in a highway tunnel

During the period May 18-May 22, 1999, a comprehensive study was conducted in the Tuscarora Mountain Tunnel on the Pennsylvania Turnpike to measure real-world motor-vehicle emissions. As part of this study, size distributions of particle emissions were determined using a scanning mobility particle sizer. Each measured size distribution consisted of two modes: a nucleation mode with midpoint diameter less than 20 nm and an accumulation mode with midpoint diameter less than 100 nm. The nucleation and accumulation components in some distributions also exhibited second maxima, which implies that such particle size distributions are superpositions of two particle size distributions. This hypothesis was utilized in fitting the particle size distributions that exhibited second maxima with four lognormal distributions, two for the nucleation mode and two for the accumulation mode. The fitting assumed that the observed particle size distribution was a combination of two bimodal log-normal distributions, one attributed to the heavy-duty diesel (HDD) vehicles and another attributed either to a different class of HDD vehicles or to the light-duty spark ignition vehicles. Based on this method, estimated particle production rates were 1.8 x 10(13) and 2.8 x 10(14) particles/vehicle-km for light-duty spark ignition and HDD vehicles, respectively, which agreed with independently obtained estimates.     

Real-world vehicle emissions: a summary of the Seventeenth Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council, Inc. (CRC) held its 17th On-Road Vehicle Emissions Workshop in March 2007, where results of the most recent on-road vehicle emissions research were presented. We summarize ongoing work from researchers who are engaged in improving our understanding of the role and contribution of mobile sources to ambient air quality and emission inventories. Participants in the Workshop discussed efforts to improve mobile source emission models, light- and heavy-duty vehicle emissions measurements, on- and off-road emissions measurements, effects of fuels and lubricating oils on emissions, as well as emerging issues and topics for future research.     

Effects of a herbicide-insecticide mixture in freshwater microcosms: risk assessment and ecological effect chain

Effects of chronic application of a mixture of the herbicide atrazine and the insecticide lindane were studied in indoor freshwater plankton-dominated microcosms. The macroinvertebrate community was seriously affected at all but the lowest treatment levels, the zooplankton community at the three highest treatment levels, with crustaceans, caddisflies and dipterans being the most sensitive groups. Increased abundance of the phytoplankton taxa Cyclotella sp. was found at the highest treatment level. Threshold levels for lindane, both at population and community level, corresponded well with those reported in the literature. Atrazine produced fewer effects than expected, probably due to decreased grazer stress on the algae as a result of the lindane application. The safety factors set by the Uniform Principles for individual compounds were also found to ensure protection against chronic exposure to a mixture of a herbicide and insecticide at community level, though not always at the population level.     

Variation in indoor levels of polycyclic aromatic hydrocarbons from burning various biomass types in the traditional grass-roofed households in Western Kenya

Biomass burning as fuel in the traditional grass-roofed rural households of Western Province of Kenya in open fire places, in poorly ventilated conditions, lead to accumulation of soot under the roofs. This study characterized and quantified the polycyclic aromatic hydrocarbons (PAHs) in accumulated soot in these households and determined the variation in PAHs concentrations with fuel biomass type. Soot samples collected from the households were extracted, cleaned and analysed by gas chromatography. The PAHs were identified using retention times, verified by gas chromatographic mass spectral analysis and quantified from peak area responses using the internal standard method. The PAHs levels significantly varied (P ≤ 0.05) with biomass type in the order: dung ≥ indigenous trees ≥ exotic trees ≥ shrubs and crop residues. Use of dung and wood from indigenous trees as fuel should be discouraged since they are higher emitters (P ≤ 0.05) of carcinogenic PAHs.     

Landfill leachate effects on sorption of organic micropollutants onto aquifer materials

The effect of dissolved organic carbon as present in landfill leachate, on the sorption of organic micropollutants in aquifer materials was studied by laboratory batch and column experiments involving 15 non-polar organic chemicals, 5 landfill leachates and 4 aquifer materials of low organic carbon content. The experiments showed that hydrophobic organic micropollutants do partition into dissolved organic carbon found in landfill leachate potentially increasing their mobility. However, landfill leachate interacted with aquifer materials apparently increases the sorbent affinity for the hydrophobic micropollutants. The combination of these two mechanisms affected the observed distribution coefficients within a factor of two, in some cases increasing and in other cases decreasing the sorption of the chemicals. No means for prediction of the effect is currently available, but from a practical point of view, the effect of landfill leachate on retardation of organic micropollutants in aquifer material seems limited.     

The Smogless Automobile

Demands for high performance and reliability of electrostatic precipitators for collection of fly ash from low sulfur fuels has led to rapid escalation of sizes and uncertainties in sizings of cold-side precipitators. This has led to utilization of the so-called “hot-side” precipitator. The underlying concept of hot-side precipitation is the avoidance of the necessity to operate the precipitator under high resistivity conditions. Data on in-situ measurements of resistivity of low sulfur fuel ash, as well as performance parameters of a number of operating installations, will be reviewed. These data will demonstrate the reduced sensitivity of hot-side precipitator sizing to fuel conditions. Other advantages of hot-side precipitators will be discussed.

Operating experience with hot-side precipitators has focused on structural problems which are peculiar to the larger, higher temperature installations. The nature and solution of these problems will be discussed. General comparative economics of hot-side and cold-side precipitators as they relate to fuel properties will be reviewed.     

Full-Scale Study of Plume Rise At Large Coal-Fired Electric Generating Stations

This paper reports on the plume rise research project conducted by TVA under sponsorship of the U. S. Public Health Service. Plume rise data were collected at six coal-fired, steam-electric generating stations within the TVA system over a 2-year period. Unit ratings ranged from 173 to 704 Mw with stack heights varying from 250 to 600 ft. An instrumented helicopter and special photographic equipment were used to obtain 1580 separate plume observations and significant related meteorological parameters during stable, neutral, and slightly unstable conditions. The 1580 observations were resolved and consolidated into 133 composite observation periods covering 30 to 120 min. Meteorological parameters and other compiled input data were entered into four principal equations for calculation of plume rise, and calculated plume rise values were compared with observed values. Most equations overestimated plume rise in low wind speed. For moderately high wind speeds, the Carson and Moses and the Concawe equations gave best fit.     

Principal Plume Dispersion Models: TVA Power Plants

The body of information presented in this paper is directed to those individuals who may be concerned with principal plume dispersion models at coal-burning power plants. About 20 years of comprehensive field surveillance and documentation of dispersion of power plant emissions for a varied range of unit sizes, stack heights, and meteorological conditions have determined the Tennessee Valley Authority’s interpretation of principal plume dispersion models. TVA’s experience indicates that as unit sizes are increased and taller stacks are constructed, the plume dispersion model associated with maximum surface concentrations changes. Maximum surface concentrations for principal plume dispersion models were approximately equal for the early small plants. However, the coning model was considered the critical plume dispersion model because the frequency of recurrence of surface concentrations from this model was appreciably greater than other models.

There were progressive changes because of an increase in unit sizes and stack heights; the magnitude of maximum surface concentrations from the coning model decreased, and the magnitude (relative to the coning model) of concentrations from the inversion breakup model increased. However, with plumes from newer and larger units with higher stacks, the trapping dispersion model became prominent. Finally, by the time unit size had increased to 900 mw and stack height to about 245 meters, as at Bull Run Power Plant, the magnitude of surface concentrations associated with trapping had increased to such a degree that it became the critical dispersion model identified with power plants of this size.     

An Optical Transistorized Ignition System

Annually about 100 million automobiles suck in vast quantities of air and eject it in a contaminated state. When, pollutants are measured by weight,¹ it seems that the automobile is the nation’s worst polluter. The EPA estimates that in 1969 motor vehicles accounted for 98 million tons of CO, 8.7 million tons of NO_x and more than 17 million tons of HC.