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W R Ott

Publications and source records attributed to W R Ott.

18 recordsLinked to original sources
PubMed1996

A mathematical model for predicting trends in carbon monoxide emissions and exposures on urban arterial highways.

The roadway is one of the most important microenvironments for human exposure to carbon monoxide (CO). To evaluate long-term changes in pollutant exposure due to in-transit activities, a mathematical model has been developed to predict average daily vehicular emissions on highways. By utilizing measurements that are specific for a given location and year (e.g., traffic counts, fleet composition), this model can predict emissions for a specific roadway during various time periods of interest, allowing examination of long-term trends in human exposure to CO. For an arterial highway in northern California, this model predicts that CO emissions should have declined by 58% between 1980 and 1991, which agrees fairly well with field measurements of human exposure taken along that roadway during those two years. An additional reduction of up to 60% in CO emissions is predicted to occur between 1991 and 2002, due solely to the continued replacement of older cars with newer, cleaner vehicles.

Carbon Monoxide↗
PubMed1991

Averaging time modeling of exposure simulation with application to the El Camino Real vehicle data.

When profiles of activity patterns are used to generate time series of simulated exposure, one typically samples from exposure distributions which are microenvironment-specific to each activity. If the simulation time step is short, then independent sampling at each time step, ignoring autocorrelation, will result in aggregates with too little variability from one simulation to another. Autocorrelation can often be modeled with one or two extra parameters and then used in the simulation. Furthermore, one may substantially reduce computation by generating a single averaged exposure for each activity segment whose distribution depends in a simple way on the activity duration and the modeled autocorrelation. The process is illustrated using the El Camino Real commuting exposure study data of Ott, Switzer, and Willits.

Carbon Monoxide↗
PubMed1990

Total human exposure: basic concepts, EPA field studies, and future research needs.

Historically, environmental regulatory programs designed to protect public health have monitored pollutants only in geophysical carrier media (for example, outdoor air, streams, soil). Field studies have identified a gap between the levels observed in geophysical carrier media and the concentrations with which people actually come into contact: their daily exposures. A new approach--Total Human Exposure (THE)--has evolved to fill this gap and provide the critical data needed for accurately assessing public health risk. The THE approach considers a three-dimensional "bubble" around each person and measures the concentrations of all pollutants contacting that bubble, either through the air, food, water, or skin. Two basic THE approaches have emerged: (1) the direct approach using probability samples of populations and measuring pollutant concentrations in the food eaten, air breathed, water drunk, and skin contacted; and (2) the indirect approach using human activity pattern-exposure models to predict population exposure distributions. Using the direct approach, EPA has conducted over 20 field studies for pollutants representing four groups--volatile organic compounds, carbon monoxide, pesticides, and particles--in 15 cities in 12 states. The indirect modeling approach has been applied to several of these pollutants. Additional research is needed in a great variety of areas. Even from the few projects completed thus far, the THE approach has yielded a rich new data base for risk assessments and has provided many surprises about the relative contribution of various pollutant sources to public health risk.

Environmental Pollution↗
PubMed1990

A physical explanation of the lognormality of pollutant concentrations.

Investigators in different environmental fields have reported that the concentrations of various measured substances have frequency distributions that are lognormal, or nearly so. That is, when the logarithms of the observed concentrations are plotted as a frequency distribution, the resulting distribution is approximately normal, or Gaussian, over much of the observed range. Examples include radionuclides in soil, pollutants in ambient air, indoor air quality, trace metals in streams, metals in biological tissue, calcium in human remains. The ubiquity of the lognormal distribution in environmental processes is surprising and has not been adequately explained, since common processes in nature (for example, computation of the mean and the analysis of error) usually give rise to distributions that are normal rather than lognormal. This paper takes the first step toward explaining why lognormal distributions can arise naturally from certain physical processes that are analogous to those found in the environment. In this paper, these processes are treated mathematically, and the results are illustrated in a laboratory beaker experiment that is simulated on the computer.

Models, Theoretical↗
PubMed1981

[Late postoperative complications in Hirschsprung's disease (author's transl)].

In more than 5,500 patients operated upon for Hirschsprung's disease which were obtained from the literature, the late complications following the 4 principal operative procedures of Swenson, Duhamel, Rehbein and Soave were compared. After Duhamel's operation, there was a lower incidence of postoperative constipation: 6.7%, compared with an average rate of 9.3%. Rehbein's resection showed the best results in relation to incontinence with a complication rate of 2.1% while the average was 9.8%, also in enterocolitis and diarrhoea (2.4%, average 7.8%) and enuresis (5.1% compared with 9.7%). We found the lowest incidence of late ileus (2.2% to 4.4%) and mortality with the Rehbein method. Judging by the frequency of late complications, the technique of Rehbein's anterior resection seems to be the most commendable.

Constipation↗
PubMed1975

Composite materials for dental implants.

The requirements of endosteal dental implants are unique and stringent. The materials currently applied to implantation do not offer convincing evidence of satisfying these needs. This preliminary study reports on attempts at developing materials which would aid in obtaining a mucosal seal to maintain the integrity of the osseous, periosteal, and submucosal compartments from the oral environment and the attachment to bone as related to stress distribution. The materials that were under study were ceramic bonded to base metals and Dacron.

Aluminum↗
PubMedDate not supplied

Comparison of microenvironmental CO concentrations in two cities for human exposure modeling.

The microenvironmental components of the CO concentration in two cities are compared by subtracting the ambient background concentration from personal exposures measured in Denver, Colorado, and Washington, DC. Two surrogate measures for the ambient background concentration are tested. Both improve the similarity of the means in the two cities, but the Denver standard deviations are higher than those in Washington, DC. Microenvironments containing the internal combustion engine have both higher means and standard deviations in Denver compared with Washington, DC. The Washington, DC, mean concentration for automobiles, for example, was 59% of the Denver mean (2.0 ppm versus 4.9 ppm). Washington, DC, had approximately 57% of the Denver emissions, and the difference in mean CO concentrations is roughly consistent with the lower emissions in Washington, DC, due to lower elevation. A surprising finding is that mean CO exposure levels caused by cooking with gas stoves in Washington, DC, were only 58% of the levels in Denver (1.9 ppm and 3.3 ppm, respectively). This result suggests that elevation may exert an influence on gas stove emissions that is similar to its influence on internal combustion engines. Using an averaging time model, analysis of the autocorrelation of sleeping and office microenvironments suggests that considerable serial dependency exists. The microenvironmental data and findings in this paper have important implications for constructing human exposure-activity pattern models. For future human exposure field studies, the findings emphasize the importance of measuring background values in a location that is extremely close to each microenvironment studied.

Adult↗
PubMedDate not supplied

Residential air exchange rates for use in indoor air and exposure modeling studies.

Data on air exchange rates are important inputs to indoor air quality models. Indoor air models, in turn, are incorporated into the structure of total human exposure models. Fragmentary data on residential ventilation rates are available in various governmental reports, journal articles, and contractor reports. Most of the published papers present data on only a few homes to answer very specialized questions, and none of these publications summarize the ventilation rates of a large population of homes across the United States. Brookhaven National Laboratory (BNL) has conducted more than 4000 residential perfluorocarbon tracer (PFT) measurements and brought them together into a large data base from about 100 studies in the United States and elsewhere. This paper analyzes the BNL PFT data base to generate frequency distributions and summary statistics for different regions of the United States, different seasons, and different levels within the homes. The data analyses suggest that residential ventilation rates are similar in the northeastern and northwestern states but higher in the southwestern states. Winter and fall ventilation rates are similar, but the rates are slightly higher in spring, and much higher in summer. Multi-level residences have higher air exchange rates than single-level residences. Although the BNL data are not a representative sample of homes in the United States, these analyses give insight into the range of air exchange rates found in the United States under a great variety of conditions and are intended for use by developers of models of indoor air quality and total human exposure.

Air Pollution, Indoor↗
PubMedDate not supplied

Human exposure assessment: the birth of a new science.

I am honored to have been selected to receive the 1995 Weselowski Award for Career Achievement in Exposure Assessment. When I think back to my friendship with Jerry Weselowski, I remember our discussions in 1991 about the need to define exposure rigorously and quantitatively. In fact, I sent Jerry a letter on that topic--the quantitative definition of exposure--on November 7, 1991. I think it is fitting, therefore, that I select one of the topics in my talk today from that letter. Jerry always welcomed full and open scientific debate and discussion, and I feel that the need to define exposure and to understand what it means is a topic of great importance in exposure assessment. I also want to offer some observations about the importance of our field for the public and the regulatory community and to suggest the directions that exposure assessment might take as it evolves as a profession. Finally, I hope to provide an up-to-date listing of some selected scientific papers that are relevant to our field.

Adult↗