Alfred T. Hodgson

Modeling Emissions of Volatile Organic Compounds from New Carpets

A simple model is proposed to account for observed emissions of volatile organic compounds (VOCs) from new carpets. The model assumes that the VOCs originate predominantly in a uniform slab of polymer backing material. Parameters for the model (the initial concentration of a VOC in the polymer, a diffusion coefficient and an equilibrium polymer/air partition coefficient) are obtained from experimental data produced by a previous chamber study. The diffusion coefficients generally decrease as the molecular weight of the VOCs increase, while the polymer/air partition coefficients generally increase as the vapor pressure of the compounds decrease. In addition, for two of the study carpets that have a styrene-butadiene rubber (SBR) backing, the diffusion and partition coefficients are similar to independently reported values for SBR. The results suggest that predictions of VOCs emissions from new carpets may be possible based solely on a knowledge of the physical properties of the relevant compounds and the carpet backing material. However, a more rigorous validation of the model is desirable.

Volatile organic compounds in twelve California office buildings: Classes, concentrations and sources

Concentrations of total volatile organic compounds (TVOC) and of 39 individual volatile organic compounds (VOCs) were measured in 12 northern California office buildings of three different ventilation types. The objectives were to characterize indoor air exposures to VOCs, to investigate variations in chemical composition and concentrations among the buildings, and to identify potential sources of tlne VOCs. Indoor TVOC concentrations ranged from 230 to 7000 μg m−3 with a geometric mean of 510μg m−3. The highest TVOC concentrations were measured in two buildings with wet-process photocopiers. Geometric mean concentrations of individual VOCs were, with one exception, less than 5 ppb. There was considerable variation in the chemical composition of the VOC mixtures among the buildings. For most buildings, the oxidized hydrocarbons were the dominant class. Factor analysis identified motor vehicle emissions from outdoor air as a major source of seven aromatic and five alkane hydrocarbons. There was evidence of freon leaking from air conditioning or refrigeration systems in several of the buildings.

Soil-Gas Contamination and Entry of Volatile Organic Compounds into a House Near a Landfill

Toxic volatile organic compounds (VOC) are commonly found in landfills, including those accepting only municipal waste. These VOC can migrate away from the site through the soil and result in contaminated off-site soil gas. This contaminated soil gas can enter houses built near landfills and is a potential source of human exposure to VOC. This study investigated soil-gas contamination and the mechanisms of entry of VOC into a house with a basement sited adjacent to a municipal landfill. The VOC were identified and quantified in the soil gas and in indoor and outdoor air. Pressure coupling between the basement and the surrounding soil was measured. Using soil-gas tracers, the pressure-driven advective entry of soil gas was quantified as a function of basement depressurization. From the measurements, estimates were made for the diffusive and advective entry rates of VOC into the house. A comparison of the chlorinated hydrocarbons found in soil gas at the site and in the landfill suggests that the landfill i...

Considerations in evaluating emissions from consumer products

Abstract While several indoor air quality studies suggest consumer products (e.g. aerosol sprays, paint removers, etc.) can be significant sources of volatile organic compounds, until recently characterizing emissions from consumer products has received relatively little attention. Many considerations that must be addressed in designing studies of consumer product emissions are similar to those addressed in studies of the emissions from building materials and combustion appliances. These similarities are discussed and, in addition, the considerations unique to studies of consumer product emissions are discussed with reference to an ongoing study of consumer products that contain methylene chloride. These unique considerations include bulk chemical analysis, the form of the product (e.g. liquid, aerosol or paste) and the related consumer usage pattern. The issue of personal exposure of the product user vs the average area concentration resulting from product use must be considered, as well as the challenge of incorporating results into predictive models that adequately treat the effect of different usage patterns. Finally, post-study considerations, such as exploring new issues discovered in the study, studying similar products, and validating predictive models through extension into field studies are summarized.

Correction for external mass transfer resistance in diffusive sampling

An important source of error inherent in diffusive sampling is depletion of the analyte in the region around the open end of the sampler. Error due to depletion occurs when external mass-transfer resistance is significant compared with the samplers internal mass-transfer resistance. A simple method to correct this error is presented. Multiple diffusive samplers of differing lengths are exposed simultaneously. A plot of calculated concentration of the analyte at the open end of the sampler vs. diffusive flux is extrapolated to a sampler of infinite length, yielding an estimate of concentration in the bulk atmosphere. This method was demonstrated with a diffusive sampler for water vapor by comparing extrapolated concentrations of water vapor with concentrations measured with a dew-point hygrometer.

Mercury emissions from a modified in-situ oil shale retort

Commercial oil-shale production has the potential to release significant amounts of mercury to the atmosphere. Two techniques to measure mercury in oil-shale-retort offgas, Zeeman atomic absorption spectroscopy and gold-bead amalgamation collection and analysis, are discussed and compared. A technique for speciating between organic and atomic forms of Hg is also discussed. The measured mercury emission rates and speciation results are presented.