A timed exposure diffusive sampler (TEDS) sensitive enough to measure hourly averages of nitrogen dioxide (NO2) at low parts per billion levels was developed for use in epidemiological studies. TEDS can be used for a variety of atmospheric pollutants. TEDS was tested in the laboratory against known concentrations of NO2 and against well established NO2 measurement systems. It was then tested in the field against the Environmental Protection Agency's reference method for measuring NO2. The TEDS method appears well suited to epidemiological investigations of air quality and extends previous work in this area by offering improved time resolution of changes in pollutant concentration at a cost sufficiently low to permit its use in large scale studies. The TEDS method also shows potential for miniaturization for use in personal sampling.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Mark Andrew Philip. / M.S.

Many chemicals off-gas or leech into indoor environments from sources such as consumer products, furnishings, and building materials. An understanding of the pathways from the sources to human exposure is vital in order to implement control strategies and lower exposure. Objects containing Brominated flame retardants (BFRs), one class of semivolatile organic compounds (SVOCs), burn more slowly during combustion. BFRs, especially polybrominated diphenyl ethers (PBDEs), are used in electronic devices including casings and circuit boards. Heat from internal circuitry increases the BFR vapor pressure and the partition coefficient, enhancing its transport out of the substrate and into the indoor environment. In this work, a computer tower in an office setting provides a case study to examine the emissions of, and exposure to, PBDEs. the case of a computer tower, the cooling fan increases the mass transfer coefficient, further increasing emissions. During computer use, the emission rate of PBDEs from the interior of the case is more than double the emission rate from the exterior of the case due to elevated internal temperatures and higher mass transfer due to the cooling fan. The concentration of PBDEs in the room air increases 40 - 80% for every 5°C increase inside the computer case, depending on the PBDE congener. Such enhanced emissions are a concern since recent studies have shown adverse health effects of PBDEs on human health. The major contributions of this work are: A model was developed that is useful for SVOC emissions for various heat and mass transfer situations, including diffusion through the slab and convective boundary conditions on each side of the slab, which may be simplified if the situation warrants; A systematic propagation of the uncertainties and variability of the model parameters was accomplished by using a Monte Carlo method for the input of the parameters into the model; A polydisperse indoor particle distribution was used as a sink, identifying the size-discretized particle phase PBDE concentration; An exposure assessment showed that the inhalation pathway for PBDEs in the gas and particulate phases is relevant and that the particulate phase exposure is dominant. / text

published_or_final_version / Architecture / Master / Master of Philosophy

No description available.

No description available.

No description available.

No description available.

A photoacoustic spectrometer was developed and built for measuring absorption of light by collected particles. Major advantages of the photoacoustic method are that it measures absorption directly, it is insensitive to scattered light, and it is readily used at different wavelengths. To evaluate the performance of the spectrometer, comparisons were made between photoacoustic absorption spectra and spectra calculated with Mie thoery. Pure powders with varied optical properties were used in the comparison, including carbon, hematite, and others. Results were reasonable in both absolute magnitude and spectral shape. Aerosol particles were collected in different environments in southern Arizona under background conditions in the mid-troposphere, and in a moderately polluted city. Results for the two locations, and two size ranges, are compared and contrasted in this thesis. Absolute magnitudes of absorption coefficients, measured at green wavelengths, are used to summarize many important results. Absorption by fine urban aerosol was 6 ± 4 x 10⁻⁷ m⁻¹, and four times larger than absorption by coarse urban aerosol. Normalized photoacoustic absorption spectra for urban aerosol are uniform with wavelength; background aerosol spectra have a relative increase in absorption at near UV wavelengths compared to near IR wavelengths. Urban aerosol absorption can be attributed to carbon particles larger than approximately 0.1 micron. Absorption by hematite (alpha iron oxide) particles in more strongly wavelength dependent than absorption by carbon particles, of the same size. This wavelength dependence is still not great enough to be attributed to hematite alone--although submicron hematite particles may be the dominant absorber in coarse background aerosol. (Abstract shortened with permission of author.)

The fibrous aerosol monitor (FAM) was designed to count fibrous particulates as accurately as the standard method, P & CAM 239, now NIOSH 7400. The Hi-Vol (HV) method, a modification of the standard method, was developed to collect fibers over a shorter time interval (i.e., 10-minutes) with the same accuracy as the standard method. The current study sought to compare the HV method with the FAM to assess its validity in measuring airborne asbestos levels and to assess the importance of short-term variation in asbestos levels in determining appropriate respiratory protection. Correlation between the FAM and HV showed a poor linear relationship in all comparison studies. However, there was good correlation between the average of short-term HV samples and long-term time-weighted average (TWA) samples at reported low levels of airborne asbestos. All membrane filter techniques showed strong correlation with each other, but were weakly correlated with the FAM. (Abstract shortened with permission of author.)