John A. Cooper

The effective variance weighting for least squares calculations applied to the mass balance receptor model

Abstract The effective variance weighted least squares solution to the mass balance receptor model is derived from the theory of maximum likelihood. The solution is one which contains the effects of random uncertainties in both the receptor concentrations and the source compositions. The solution involves trancendental equations of the unknown source contribution variables, and an iterative solution is required. This solution and the ordinary weighted least squares solution are applied to ten sets of simulated data generated from known source contributions and source compositions, perturbed by random experimental errors typical of those to be found in environmental sampling. The standard deviation of the source contributions calculated from each of these data sets is compared with the uncertainty obtained from the ordinary and effective variance least squares solutions; the effective variance solution provides the more accurate estimate. Extensions of this method to other least squares treatments of environmental data are proposed.

Environmental Impact of Residential Wood Combustion Emissions and its Implications

Currently available information suggests a substantial environmental impact from residential wood combustion emissions. Air pollution from this source is widespread and increasing. Current ambient measurements, surveys, and model predictions indicate winter respirable (<2 μm) emissions from residential wood combustion can easily exceed all other sources. Both the chemical potency and deliverability of the emissions from this source are of concern. The emissions are almost entirely in the inhalable size range and contain toxic and priority pollutants, carcinogens, co-carcinogens, cilia toxic, mucus coagulating agents, and other respiratory irritants such as phenols, aldehydes, etc. This source is contributing substantially to the nonattainment of current particulate, carbon monoxide, and hydrocarbon ambient air quality standards and will almost certainly have a significant impact on potential future standards such as inhalable particulates, visibility, and other chemically specific standards. Emission from...

Receptor Oriented Methods of Air Particulate Source Apportionment

Receptor models have evolved rapidly over the past 13 years but have just recently been recognized as a distinct discipline. The general category of receptor models includes both microscopic and chemical methods of apportioning source contributions to ambient air particulates. The number and variations of these methods have grown rapidly over the past few years and include such methods as automated scanning electron microscopy, chemical mass balance and multivariate procedures. These methods as well as hybrid procedures such as target transformation factor analysis, are reviewed and their boundary conditions, strengths, and weaknesses discussed.

Assessment of contemporary carbon combustion source contributions to urban air particulate levels using carbon-14 measurements.

w Measurement of carbon-14 activities with new low-level counting methods has been demonstrated to be an effective tool for assessing the contribution of contemporary carbon combustion sources to the mass collected with typical highvolume air samplers. This study represents the first time that radiocarbon measurements have been applied to fine particles (<2 pm) and used to assess the contribution of specific sources to urban air quality. Radiocarbon analysis of fine particles minimized interferences from large particles such as pollen, spores, wood fiber, etc., and improved the method’s ability to assess the impact of burning vegetative material such as field and slash burning and space heating with wood. Slash burning contributed between 39% and 70% of the fine particulate mass while field burning contributed 50% of the total suspended particulates (TSPs) on high-impact days in the Portland and Eugene, OR, airsheds. Radiocarbon analysis of filters selected for high impact from residential wood combustion shows that this source is a substantial contributor to fine particulate mass during winter months in Portland, OR.

Interlaboratory comparison of Receptor Model results for Houston aerosol

Abstract In exercises for the Mathematical and Empirical Receptor Models Workshop (Quail Roost II), nine investigators independently applied receptor models to apportion ambient aerosol mass concentrations to components from emission sources in Houston, TX. The receptor model results were based upon ambient aerosol compositional data supplied to investigators that included mass, elemental and ionic species concentrations for consecutive 12-h sampling periods at the University of Houston between 10 and 19 September 1980. Some investigators performed additional analyses by X-ray powder diffraction, scanning electron microscopy with automated image analysis and X-ray energy spectroscopy and light microscopy. In most cases, the fine (0.2–2.5 μm) and coarse (2.5–15 μm) fractions were analyzed separately by the receptor models. The models tested include effective variance type chemical mass balance, weighted ridge regression, multiple linear regression, factor analysis and target transformation factor analysis. The number of source classes determined ranged from 4 (by multiple linear regression) to 23 (by light microscopy). Results are presented and compared in eight general emissions categories.

Considerations for design of source apportionment studies

This report recommends procedures for source and ambient sampling and analysis in source apportionment studies. The recommendations are based on the results of receptor model studies of atmospheric particles in urban areas, especially a recent study of Houston, TX, undertaken as part of the Mathematical and Empirical Receptor Models Workshop (Quail Roost II). The recommendations are presented at three levels of increasing cost and detail of information obtained. Existing mass emissions inventories combined with chemically resolved test data from similar sources (not necessarily in the same locale) can be used to initially estimate the sources of elements present on ambient particles. To aid local users in construction of chemically resolved emission estimates, the U.S. Environmental Protection Agency (EPA) is compiling a library of compositions and size distributions of particulate emissions from major source types. More reliable source characterization can be achieved if the actual sources are tested directly. EPA should develop and publish detailed procedures for source sampling that would be more appropriate for receptor model use than are existing standard methods. Source and ambient sampling should be conducted by similar methods. If possible, particles from sources should be collected in a way that simulates changes that would normally occur before they reach distant receptors (e.g. by diluting and cooling the particles from hot sources). It is recommended that particulate samples be routinely collected in two size fractions by use of virtual impactors and that all samples be subjected, at a minimum, to mass and X-ray fluorescence analyses. Additional measurements are suggested for obtaining more detailed information: neutron activation analysis; X-ray diffraction; automated particle classification by electron microscopy; analyses for classes of organic species, ^(14)C and thermally released carbonaceous species; and real-time observation of several gases during sample collection. Methods for collecting meteorological data in parallel with ambient samples are described, as are methods for incorporating such data into the source identification process.

Aerosol chemical composition and light scattering in Portland, Oregon: The role of carbon

Abstract Measurements of light scattering and the chemical composition of the fine aerosol from the Portland (Oregon) Aerosol Characterization Study (PACS) of 1977–1978 are reported. Scattering coefficients for sulfate, nitrate, carbonaceous aerosol and residual mass were determined by stepwise multiple linear regression. Unlike other cities the scattering efficiencies for sulfate, nitrate and carbonaceous aerosol were approximately the same. Carbonaceous aerosol was found to account for about 50% of both the fine aerosol mass and the light scattering.

Mini-Radiocarbon Measurements, Chemical Selectivity, and the Impact of Man on Environmental Pollution and Climate

Underlying principles and results are presented for our program to use isotopic and chemical methods to quantify anthropogenic and natural sources of carbonaceous pollutants. Radiocarbon data have been obtained with a specially. developed miniature low-level gas counting system which has permitted us to assay samples containing as little as 5mg carbon. Measurements of carbonaceous particles, using chemical selectivity and size fractionation to supplement the radiocarbon data, have revealed major impact from both fossil fuel and vegetative (contemporary) sources on urban aerosols. Residential wood-burning has been specifically identified as an important source of respirable particles. Current investigations are directed toward the carbonaceous gases and the application of the accelerator technique for the assay of radiocarbon in individual chemical fractions containing microgram quantities of carbon.

Particulate dispersion model evaluation: a new approach using receptor models

Recent advances in the development of receptor-oriented source apportionment techniques (models) have provided a new approach to evaluating the performance of particulate dispersion models. Rather than limiting performance evaluations to comparisons of particulate mass, receptor model estimates of source impacts can be used to open new opportunities for in-depth analysis of dispersion model performance. Recent experience in the joint application of receptor and dispersion models have proven valuable in developing increased confidence in source impact projections used for control strategy development. Airshed studies that have followed this approach have identified major errors in emission inventory data bases and provided technical support for modeling assumptions. The paper focuses on the joint application of dispersion and receptor models to particulate source impact analysis and dispersion model performance and evaluation. The limitations and advantages of each form of modeling are reviewed and case studies are examined.

Current and projected impacts of residential wood combustion on Pacific Northwest air quality

The use of wood as a residential space heating fuel has increased significantly in the Pacific Northwest in recent years. Trends reflected in wood stove sales, firewood use, air quality measurements, and emission inventory data all collectively point toward a problem of growing concern to those responsible for protecting our air resources. In response to increasing local and state regulatory agency concern, EPA Region X commissioned a three-year, multifaceted study of the residential wood combustion issue. This paper describes the technical design of the ambient air quality impact analysis phase of the study and the methodology employed to develop projections of likely future impacts in Portland, Spokane, Seattle, and Boise, as well as associated air resource management implications. Although the body of information presented is directed to Pacific Northwest airsheds, the methodology and program results are directly applicable to many communities in which wood smoke emissions may be of concern.