Electrical Measurement of the Mass Concentration of a Self-Preserving Aerosol Size Distribution

Recently fifty-eight measurements of urban aerosol size distributions by Clark have shown that these distributions agree quite well with the self preserving form proposed by Friedlander within the size range of 0.05 to 5 microns radius. This paper shows that for an aerosol obeying the self preserving distribution model, the volume concentration (and, hence, the mass concentration for constant density) is directly proportional to the electric current collected when the aerosol is unipolarly charged, passed through a weak electric field to remove particles smaller than 0.05 micron and then collected by a current collector. It is shown that the linear relation between the mass concentration and collected current is independent of the unipolar charging method used. A test of this theory using Clark’s electric counter data was encouraging and suggests that the electric measurement of urban aerosol mass concentrations by properly designed instruments may be feasible.     

Design Variables Associated with Fiberglass/Fly Ash Fabric Filter Cleaning

This paper documents the variation in pressure drop and collection efficiency for fiberglass/fly ash fabric filter systems caused by variations in cleaning intensity (reverse air and reverse pulse), air to cloth ratio, and dust loading. Reverse air rates greater than 2 fpm were required to produce stable pressure characteristics. Pulse jet pressure greater than 50 psi reduced collection efficiency. Increased air to cloth ratios produced decreased collection efficiency.     

A System for Abatement Control Strategy Evaluation

The Air Quality Control Program of the Commonwealth of Massachusetts has developed an implementation plan for the Metropolitan Boston Intrastate Air Quality Control Region as required by PL 90-148. An essential part of the plan was a set of control regulations designed to achieve and maintain an air quality compatible with adopted standards. Control strategy modeling was used as a tool in selecting the most appropriate regulations to achieve this goal. The body of information presented in this paper is directed to those state and county air pollution control officials concerned with the formulation and evaluation of regulations.

The paper details the procedures developed and presents a case history of their use in the region. The system is a synthesis of generally-available software and newly-developed computer programs to provide ahighly automated computational structure. It permits rapid simulation of the emissions resulting from the application of various control regulations. Predictions on the changes expected in ambient air quality levels are then made by the use of the Air Quality Display Model (AQDM).

The initial step in the application was a calibration of the system using predicted and measured annual concentrations. This step yielded correlation coefficients of 0.92 for sulfur dioxide and 0.85 for particulates. Subsequently, the system was used to evaluate the baseline case of uncontrolled sulfur in fuel use. Alternative sulfur control strategies were tested for compatibility with air quality standards. The principal strategies tested were: (a) 1% sulfur uniformly throughout the region; (6) 1% sulfur in core area of region, 2.2% sulfur elsewhere; (c) 0.5% sulfur in core area of region, 2.2% sulfur elsewhere; (d) 0.5% sulfur in core area of region, 1.0% sulfur elsewhere.

Strategies (b) and (d) were implemented into a time phased set of control regulations for the region.

Experience with the system has shown it to be a convenient and rapid method for simulating the effects of control regulations. Furthermore, the utility of this initial model warrants expansion of its application to the other air quality control regions in the Commonwealth.     

Scenario identification and evaluation for layers of protection analysis

The identification and screening of scenarios has been identified as a source of variation in Layers of Protection Analysis (LOPA). Often the experience of the analyst is a significant factor in determining what scenarios are evaluated and the worst credible consequences. This paper presents a simplified chemical process risk analysis that is effective in providing a semi-quantitative measure of consequence that may include human harm and is independent of the analyst. This process may be used in evaluation of Management of Change, inherently safer design decisions for capital projects and LOPA re-validation. Conditional and relational logic may be captured with the use of simple spreadsheets to further improve overall efficiency. For example, this method minimizes the overall time required for scenario development and re-validation relative to Hazard and Operability studies (HAZOP).The technique simplifies established models used by engineers engaged in the operation or design of a chemical manufacturing facility without special software or training. The results of this technique are realistic and may be directly compared with corporate or regulatory guidelines for risk of fatality or injury. At each step in the risk analysis process, more detailed or sophisticated methods may be used to refine the technique. Furthermore, results from any step may indicate that the hazard from a specific scenario case is not sufficient to continue with subsequent analysis steps.     

Sustainability of natural resource use for an Amazonian indigenous group

This research examines how the Kandozi indigenous group governs access to fish and timber for sale and evaluates their perceptions of sustainability of those natural resources. The Kandozi occupy a biodiverse tropical forest in the northern Peruvian Amazon with lakes and seasonally flooded areas. Qualitative methods and a comparative examination of access to resources were used to explore current processes that shape access and the people’s perceptions of their benefit from natural resources. Results indicated that environmental heterogeneity, kinship, land tenure, the legal framework, and knowledge all shaped access with some differences due to the dissimilar natures of fish and timber. This research concludes that the sustainability of this and similar systems are dependent upon the moment at which the analysis is done, because of the changing needs of people over time, in addition to changes in external factors and the natural variations that occur in the resources used. The range of relations and interactions among different processes that shape access, and the historically contingent characteristic of access and its evolution over time, help better understand the complexity of a given social-ecological system.     

Cohesion of Precipitated Dust Layer in Electrostatic Precipitators

One of the important cohesive forces acting on the precipitated layer in an electrostatic precipitator Is that due to the effect of the electric field established in the air gaps between adjacent particles by the corona current as it flows through the layer. A theoretical expression for this force is developed for an idealized dust layer which takes into account the increase in effective contact area between adjacent particles due to elastic deformation and the limiting of the electric field in the airgap to a maximum allowable value. It is shown that the cohesive force is approximately proportional to the electric field established across the layer. This relationship is in general agreement with measurements made in the laboratory using industrially produced dust samples.     

A Characterization of Emissions from an Early Model Flexible-Fuel Vehicle

An emission study was conducted on a 1987 Ford Crown Victoria flexible-fuel vehicle, an early prototype which had been driven about 25,000 miles. The vehicle was run on both gasoline and a blend of 85 percent methanol and 15 percent gasoline. Emission rates of regulated pollutants (hydrocarbons, carbon monoxide, nitrogen oxides, formaldehyde, and methanol) and nonregulated pollutants (speciated organic materials) were determined for both exhaust and evaporative emissions. Tests were run varying the driving cycle, ambient temperature and catalytic converter. In general, hydrocarbon composition of exhaust emissions was significantly affected by catalyst replacement and cold starts, slightly affected by driving schedule, and unaffected by ambient temperature and test fuel. Hydrocarbon composition of evaporative emissions was only sensitive to the type of evaporative test being performed: diurnal tests typically had larger fractions of lower molecular weight paraffins than hot soak tests.     

Atmospheric Aerosols: Size Distribution Interpretation

The body of information presented in this paper is directed towards the scientist or engineer who measures and interprets the physical characteristics of ambient air. This paper interprets measurements made with the Minnesota Aerosol Analyzing System (MAAS) in Denver, near Denver, and near Ft. Collins, Colo., and examines the measurements in the light of what has been learned from several thousand size distributions measured in the other parts of the United States. The origin and physical change of atmospheric particulates is examined through interpretation of modes occurring in the size distributions. The mode coined “AHken Nuclei Range” mode is a measure of aerosol generation, while aged aerosols show up in the “Accumulation Range” mode. Windblown dusts, sea sprays, and mechanically produced particles such as fly ash generate a “Coarse Particle Range” mode. The air environment is categorized into several types of background and urban aerosols whose physical characteristics are described by a limited number of parameters. These categories are exemplified and discussed.