Robert W. Coutant

Phase distribution and artifact formation in ambient air sampling for polynuclear aromatic hydrocarbons

Abstract Laboratory and field sampling experiments were conducted to determine the phase-distribution of polynuclear aromatic hydrocarbons (PAH) in the ambient atmosphere and to determine the potential for artifact formation due to volatilization and ozone (O3) reaction during normal sampling conditions. The study was conducted in two segments to investigate both summer and winter ambient temperature effects. The winter measurements reflect stronger association of PAH with the particulate phase than the summer data, but data from both seasons show appreciable filter losses due to volatilization of phenanthrene, anthracene, fluoranthene, benz(a)anthracene and chrysene. No evidence was found for volatilization of the heavier PAH, including benzo(e)pyrene, benzo(a)pyrene, indeno(l,2,3-c,d)pyrene, benzo(g,h,i)perylene and coronene. Although O3 reacted readily with particulate matter that was freshly spiked with PAH in the laboratory experiments, no evidence was found for reaction of O3 with particulate matter during the field sampling experiments.

Design and performance of a high-volume compound annular denuder

Abstract A laminar flow model incorporating variable collisional reaction efficiency is developed and applied for the design of annular denuders. Efficiencies predicted with the model show excellent agreement with published empirical data for annular denuders that are used for collection of SO 2 , but point to potential errors in extending the empirical data to different chemical systems. The design and construction of a compound annular denuder for collection of polynuclear aromatic hydrocarbon (PAH) vapor are described. This denuder, which consists of a nested set of cylindrical tubes, is shown to operate efficiently at sampling rates of up to 3.33 l s −1 while maintaining essentially 100 per cent transmission of micron-sized particulate matter.

Rates and mechanisms of NO2 removal from indoor air by residential materials

Recent studies have shown that NO{sub 2} is removed from indoor air more rapidly than by air exchange alone. The relative efficiencies for NO{sub 2} removal by a large number of materials are presented here, along with a discussion of the factors that influence the removal process. This work has demonstrated that reaction with indoor surfaces represents a significant sink for NO{sub 2}, and that these reactions currently are effecting a considerable degree of control over indoor NO{sub 2} levels. It seems likely that this control could be enhanced by judicious selection of furnishings and construction materials. Improved understanding of the rates and mechanisms of the removal process will permit optimization of the process for indoor air quality improvement.

Efficiency of silicone-grease-coated denuders for collection of polynuclear aromatic hydrocarbons

Abstract The overall efficiency of silicone-grease-coated denuders was determined for the collection of selected 3- and 4-ring polynuclear aromatic hydrocarbons (PAH). PAH studied were fluorene, phenanthrene, anthracene, acenaphthene and pyrene. Fluorene was subsequently eliminated from consideration because of analytical problems caused by the reactivity of this compound. Results are interpreted in terms of the collisional reaction efficiencies (γ) for these compounds. An analysis of the effects of uncertainties in diffusion coefficients and γ values for these compounds on overall phase distributions derived from experimental data suggests that the consequences of these uncertainties are less significant than normal variations due to sampling and analysis effects.

Aerosol filtration by sorbent beds

Fixed beds of sorbent media are used for the evaluation of poiynuclear aromatic hydrocarbons (PAH) present in air. Twostage sampling and separate extraction and analyses of PAH associated with aerosol particles and those present in the vapor state are usually performed. The ability of commonly used sorbents to retain particulate matter introduces a potential for reducing the time and cost of PAH evaluation procedures. The filtration efficiency of three sorbent media, Florisil, XAD-2, and polyurethanefoam (PUF), for particles in 0.1 to 1 µm size range was studied using airflow rates from 4 to 2501 /mm through a PS 1 sorbent cartridge. Theoretical considerations were used to identify the principal filtration mechanisms and to assess the predictability of the aerosol filtration performance of sorbent filters. The results of this study indicate XAD-2 to be an efficient filtration medium owing to the electrostatic enhancement of capturing and retaining aerosol particles. As a result of theoretical consideratio...

Formation of NO2 in range-top burners

This paper describes results of a study that examined NO and NO2 formation on range-top burners and in diffusion flames. These flames were characterized by composition and temperature profiles. Range-top burner flames and pilot flames displayed qualitatively similar behavior with respect to the kinds of flame regions in which relatively high NO2/NO ratios were identified. These regions of high NO2/NO ratios were consistently either regions of low oxygen concentration or flame surfaces subjected to thermal quenching. A limited series of experiments with modified burners indicated that reduced emissions from both the RTB and pilot flames could be achieved by (1) improved primary aeration, using 50% or greater primary air, and (2) using flame geometries designed to minimize flame surface, e.g., flat-flame burners or other designs having effectively fewer distinct ports. Both NO and NO2 are readily produced in diffusion and partially premixed Bunsen-type flames, mainly in the vicinity of the hot visible zone. High NO2/NO ratios are associated with the cooler regions of the flame, as, for example, at the base of the flame in the highly diluted downstream region and in the fuel-rich regions of the flames. A simplified reaction mechanism based on CN and NH radicals being oxidized to NO followed by NO + HO2 → NO2 + OH appears to explain the high NO2/NO ratios observed. A practical implication of the study is that a burner designed with improved aeration and mixing minimization of flame surface should emit less NO2.