Electrostatic Stimulation of Fabric Filtration

The concept of electrostatic stimulation of fabric filtration (ESFF) has been investigated at pilot scale. The pilot unit consisted of a conventional baghouse in parallel with an ESFF baghouse, allowing direct comparison. All results reported in this paper are for pulse-cleaned bags in which the electric field was maintained parallel to the fabric surface. The performance of the ESFF baghouse has been superior to the parallel conventional baghouse by several measures. The ESFF baghouse demonstrated: (1) a reduced rate of pressure drop increase during a filtration cycle, (2) lower residual pressure drop, (3) stable operation at higher face velocities, and (4) improved particle removal efficiency. These benefits can be obtained with only minor modifications to conventional pulse-jet hardware and at low electrical power consumption. The indicated ability to operate at increased face velocities with only modest expenditure for electrical hardware leads to very favorable economic projections.     

The Effect of Building Fan Operation on Indoor-Outdoor Dust Relationships

As part of an energy conservation program recently implemented by the Bell System, fans in many telephone equipment buildings now operate only when necessary to bring the temperature within allowable limits, rather than continuously. In the study reported here the effects of fan operation on indoor-outdoor dust relationships were monitored at 2 representative telephone offices. Automatic dichotomous samplers were used to collect fine and coarse aerosol particles inside telephone equipment buildings at Wichita, KS and Lubbock, TX. At both sites, outdoor samples (roof top) were collected at the same time as the indoor samples. During the tests the building fans were repetitively cycled between 2-week intervals of continuous fan operation and 2-week intervals of intermittent fan operation. The indoor dust concentrations typically increased when the fans were off. The results indicate that this increase was due to loss of constant filtration, but not due to loss of building pressurlzation (i.e., filtration of the recirculated air is largely responsible for the lower dust levels when the fans are running continuously). An expression is derived for the relative dust increase when the building fans are switched off. Among other factors, the relative increase is directly proportional to the efficiency of the building filters and to the rate at which air is recirculated through them. The present findings can be extended to similar buildings.     

Factors Influencing the Emissions of Nitrated-Polynuclear Aromatic Hydrocarbons(Nitro-PAH) from Diesel Engines

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).     

Formaldehyde Concentrations in Wisconsin Mobile Homes

Mobile homes utilize a class of prefabricate construction techniques which rely greatly upon the use of particle board and hardwood plywood paneling for structural components. This has resulted In household sources which may emit formaldehyde into the home, since urea-formaldehyde resins are used as the bonding agent in most pressed wood stocks. A series of 137 mobile home households was investigated to determine indoor formaldehyde exposure concentrations. Homes were selected based on the estimated age of the construction components. Homes were studied serially for a nine-month period, with formaldehyde samples obtained on a monthly basis using a modified NIOSH chromotropic acid procedure. Formaldehyde concentrations were found to range from less than 0.10 ppm to 2.84 ppm. The median exposure concentration was 0.39 ppm. Analysis of variance was performed on each home to discern visit and room measurement effects. Eighty-nine percent of the homes exhibited no measurement placement effects, while only 10 percent failed to demonstrate between-visit variance effects. Regression models were constructed to predict household formaldehyde concentrations. Concentrations exhibited an inverse relationship with the age of the construction materials. A weighted least squares regression model of log of home age predicting temperature-corrected log formaldehyde explained 82 percent of the formaldehyde variation.     

The Relationship between Cross-Sectional and Time Series Studies

Abstract

There is a dearth of information on dust emissions from sources that are unique to the U.S. Department of Defense testing and training activities. However, accurate emissions factors are needed for these sources so that military installations can prepare accurate particulate matter (PM) emission inventories. One such source, coarse and fine PM (PM₁₀ and PM_2.5) emissions from artillery backblast testing on improved gun positions, was characterized at the Yuma Proving Ground near Yuma, AZ, in October 2005. Fugitive emissions are created by the shockwave from artillery pieces, which ejects dust from the surface on which the artillery is resting. Other contributions of PM can be attributed to the combustion of the propellants. For a 155–mm howitzer firing a range of propellant charges or zones, amounts of emitted PM₁₀ ranged from ～19 g of PM₁₀ per firing event for a zone 1 charge to 92 g of PM₁₀ per firing event for a zone 5. The corresponding rates for PM_2.5 were ～9 g of PM_2.5 and 49 g of PM_2.5 per firing. The average measured emission rates for PM₁₀ and PM_2.5 appear to scale with the zone charge value. The measurements show that the estimated annual contributions of PM₁₀ (52.2 t) and PM_2.5 (28.5 t) from artillery backblast are insignificant in the context of the 2002 U.S. Environment Protection Agency (EPA) PM emission inventory. Using national–level activity data for artillery fire, the most conservative estimate is that backblast would contribute the equivalent of 5 x 10^–4% and 1.6 x 10^–3% of the annual total PM₁₀ and PM_2.5 fugitive dust contributions, respectively, based on 2002 EPA inventory data.     

A Collaborative Effort to Model Plant Response to Acidic Rain

Radish plants were exposed three times per week to simulated acidic rain at pH values of 2.6 to 5.4 over the course of four weeks in trials performed at Argonne, Illinois; Ithaca and Upton, New York; Corvallis, Oregon; Oak Ridge, Tennessee; and Toronto, Canada. Uniform genotype, soil media and planting techniques, treatment procedures, biological measurements, and experimental design were employed. Growth of plants differed among trials as a result of variation in greenhouse environmental conditions according to location and facilities. Larger plants underwent greater absolute but lower relative reductions in biomass after exposure to the higher levels of acidity. A generalized Mitscherlich function was used to model the effects of acidity of simulated rain or dry mass of hypocotyls using data from three laboratories that performed duplicate trials. The remaining data, from three other laboratories that performed only one trial each, were used to test the model. When the laboratory by trial effect was removed (influence of different growth. conditions), lack of fit to the Mitscherlich function was insignificant. Thus, a single mathematical model satisfactorily characterized the relationship between acidity and mean plant response. The pH value associated with a 10 percent reduction in mass was 3.3 ± 0.3 for hypocotyls. No value was estimated for shoots because effects oh shoots were not significant. The results of this study demonstrate that a generalized exposure-response model can be developed in the presence of large variations in environmental conditions when plant culture and exposure to simulated rain are standardized among laboratories.     

Reducing Interference Effects in the Chemiluminescent Measurement of Nitric Oxides from Combustion Systems

Experiments were carried out to determine the relative chemiluminescence quenching efficiencies as a function of third body concentration for each of the common combustion products, H₂O, CO₂, CO, H₂, O₂ and Ar. These results are compared with those of other investigators. The effect of reaction chamber pressure on analyzer response and the development of an analyzer design which incorporates an adjustable sample capillary inlet capable of maintaining a constant molar flow rate of sample gas to the reaction chamber are discussed. The effect of carbon monoxide interference on chemiluminescent NO_x measurement has been isolated and found to be significant. A means of correcting NO, measurements for these CO interference effects is described. Quantification of NO and NO₂ absorption in liquid water in NO_x sampling systems has been made. Recommendations for sample system designs to handle the presence of water in the sample gas are made.