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Biomedical subjects

William W Nazaroff

Publications and source records attributed to William W Nazaroff.

8 recordsLinked to original sources
PubMed2006

Indoor secondary pollutants from household product emissions in the presence of ozone: A bench-scale chamber study.

Ozone-driven chemistry is a source of indoor secondary pollutants of potential health concern. This study investigates secondary air pollutants formed from reactions between constituents of household products and ozone. Gas-phase product emissions were introduced along with ozone at constant rates into a 198-L Teflon-lined reaction chamber. Gas-phase concentrations of reactive terpenoids and oxidation products were measured. Formaldehyde was a predominant oxidation byproduct for the three studied products, with yields for most conditions of 20-30% with respect to ozone consumed. Acetaldehyde, acetone, glycolaldehyde, formic acid, and acetic acid were each also detected for two or three of the products. Immediately upon mixing of reactants, a scanning mobility particle sizer detected particle nucleation events that were followed by a significant degree of secondary particle growth. The production of secondary gaseous pollutants and particles depended primarily on the ozone level and was influenced by other parameters such as the air-exchange rate. Hydroxyl radical concentrations in the range 0.04-200 x 10(5) molecules cm(-3) were determined by an indirect method. OH concentrations were observed to vary strongly with residual ozone level in the chamber, which was in the range 1-25 ppb, as is consistent with expectations from a simplified kinetic model. In a separate chamber study, we exposed the dry residue of two products to ozone and observed the formation of gas-phase and particle-phase secondary oxidation products.

Air Pollutants↗
PubMed2005

Toward understanding the risk of secondary airborne infection: emission of respirable pathogens.

Certain respiratory tract infections are transmitted through air. Coughing and sneezing by an infected person can emit pathogen-containing particles with diameters less than 10 microm that can reach the alveolar region. Based on our analysis of the sparse literature on respiratory aerosols, we estimated that emitted particles quickly decrease in diameter due to water loss to one-half the initial values, and that in one cough the volume in particles with initial diameters less than 20 microm is 60 x 10(-8) mL. The pathogen emission rate from a source case depends on the frequency of expiratory events, the respirable particle volume, and the pathogen concentration in respiratory fluid. Viable airborne pathogens are removed by exhaust ventilation, particle settling, die-off, and air disinfection methods; each removal mechanism can be assigned a first-order rate constant. The pathogen concentration in well-mixed room air depends on the emission rate, the size distribution of respirable particles carrying pathogens, and the removal rate constants. The particle settling rate and the alveolar deposition fraction depend on particle size. Given these inputs plus a susceptible person's breathing rate and exposure duration to room air, an expected alveolar dosemicrois estimated. If the infectious dose is one organism, as appears to be true for tuberculosis, infection risk is estimated by the expression: R = 1-exp(-micro). Using published tuberculosis data concerning cough frequency, bacilli concentration in respiratory fluid, and die-off rate, we illustrate the model via a plausible scenario for a person visiting the room of a pulmonary tuberculosis case. We suggest that patients termed "superspreaders" or "dangerous disseminators" are those infrequently encountered persons with high values of cough and/or sneeze frequency, elevated pathogen concentration in respiratory fluid, and/or increased respirable aerosol volume per expiratory event such that their pathogen emission rate is much higher than average.

Aerosols↗
PubMed2004

Inhalation of hazardous air pollutants from environmental tobacco smoke in US residences.

In the United States, 48 million adults smoke 3.5-5 x 10(11) cigarettes/year. Many cigarettes are smoked in private residences, causing regular environmental tobacco smoke (ETS) exposure to roughly 31 million nonsmokers (11% of the US population), including 16 million juveniles. (Upper bound estimates are 53 million exposed nonsmokers including 28 million juveniles.) ETS contains many chemical species whose industrial emissions are regulated by the US federal government as hazardous air pollutants (HAPs). In this paper, average daily residential exposures to and intakes of 16 HAPs in ETS are estimated for US nonsmokers who live with smokers. The evaluation is based on material-balance modeling; utilizes published data on smoking habits, demographics, and housing; and incorporates newly reported exposure-relevant emission factors. The ratio of estimated average exposure concentrations to reference concentrations is close to or greater than one for acrolein, acetaldehyde, 1,3-butadiene, and formaldehyde, indicating potential for concern regarding noncancer health effects from chronic exposures. In addition, lifetime cancer risks from residential ETS exposure are estimated to be substantial ( approximately 2-500 per million) for each of five known or probable human carcinogens: acetaldehyde, formaldehyde, benzene, acrylonitrile, and 1,3-butadiene. Cumulative population intakes from residential ETS are compared for six key compounds against ambient sources of exposure. ETS is found to be a dominant source of environmental inhalation intake for acrylonitrile and 1,3-butadiene. It is an important cause of intake for acetaldehyde, acrolein, and formaldehyde, and a significant contributor to intake for benzene.

Adolescent↗
PubMed2002

Ozone interactions with carpet: secondary emissions of aldehydes.

Ozone-induced formation of aldehydes was studied on the surface and in the gas phase above carpets and on carpet components. Samples of four carpets were exposed to 100 ppb ozone. Emission rates of aldehydes and other organic compounds were measured from exposed and unexposed samples. Surface interactions of ozone with carpets produced C1-C13 n-aldehydes and several unsaturated aldehydes. Total aldehyde emission rates increased markedly with ozone exposure, from 1 to 70 microg m(-2) h(-1) for unexposed samples, to 60-800 microg m(-2) h(-1) during exposure. One exposed sample emitted large amounts of 2-nonenal (180-230 microg m(-2) h(-1)), a compound with a low odor threshold. Material balance modeling of a residence with this high emitting carpet suggests (1) that the concentration of 2-nonenal would be well above its odor threshold even in areas with only moderate ambient ozone levels and (2) that odorous levels of 2-nonenal could persist for years. Reactions of ozone with gas-phase primary emissions from carpet significantly reduced the levels of 4-phenylcyclohexene and produced small amounts of branched ketones. Separately measured patterns of aldehyde emissions from ozone exposure of linseed and tung oils were similar but not identical to those observed from ozone-exposed carpets.

Air Pollution, Indoor↗
PubMed2002

Gas-phase organics in environmental tobacco smoke. 1. Effects of smoking rate, ventilation, and furnishing level on emission factors.

We measured the emissions of 26 gas-phase organic compounds in environmental tobacco smoke (ETS) using a model room that simulates realistic conditions in residences and offices. Exposure-relevant emission factors (EREFs), which include the effects of sorption and re-emission over a 24-h period, were calculated by mass balance from measured compound concentrations and chamber ventilation rates in a 50-m3 room constructed and furnished with typical materials. Experiments were conducted at three smoking rates (5, 10, and 20 cigarettes day(-1)), three ventilation rates (0.3, 0.6, and 2 h(-1)), and three furnishing levels (wallboard with aluminum flooring, wallboard with carpet, and full furnishings). Smoking rate did not affect EREFs, suggesting that sorption was linearly related to gas-phase concentration. Furnishing level and ventilation rate in the model room had little effect on EREFs of several ETS compounds including 1,3-butadiene, acrolein, acrylonitrile, benzene, toluene, and styrene. However, sorptive losses at low ventilation with full furnishings reduced EREFs for the ETS tracers nicotine and 3-ethenylpyridine by as much as 90 and 65% as compared to high ventilation, wallboard/aluminum experiments. Likewise, sorptive losses were 40-70% for phenol, cresols, naphthalene, and methylnaphthalenes. Sorption persisted for many compounds; for example, almost all of the sorbed nicotine and most of the sorbed cresol remained sorbed 3 days after smoking. EREFs can be used in models and with ETS tracer-based methods to refine and improve estimates of exposures to ETS constituents.

Adsorption↗
PubMed2002

Indoor particulate matter of outdoor origin: importance of size-dependent removal mechanisms.

Adverse human health effects have been observed to correlate with levels of outdoor particulate matter (PM), even though most human exposure to PM of outdoor origin occurs indoors. In this study, we apply a model and empirical data to explore the indoor PM levels of outdoor origin for two major building types: offices and residences. Typical ventilation rates for each building type are obtained from the literature. Published data are combined with theoretical analyses to develop representative particle penetration coefficients, deposition loss rates, and ventilation-system filter efficiencies for a broad particle size range (i.e., 0.001-10 microm). We apply archetypal outdoor number, surface area, and mass PM size distributions for both urban and rural airsheds. We also use data on mass-weighted size distributions for specific chemical constituents of PM: sulfate and elemental carbon. Predictions of the size-resolved indoor proportion of outdoor particles (IPOP) for various conditions and ambient particle distributions are then computed. The IPOP depends strongly on the ambient particle size distribution, building type and operational parameters, and PM metric. We conclude that an accurate determination of exposure to particles of ambient origin requires explicit consideration of how removal processes in buildings vary with particle size.

Air Movements↗