Margo Schwab

Personal Exposure to Nitrogen Dioxide in the Los Angeles Basin

A large scale study of human exposure to nitrogen dioxide (NO2) was conducted in the Los Angeles Basin, the only metropolitan area in the United States that exceeds the NO2 NAAQS. Data are available for a population representative sample of 482 households and 682 individuals. Personal exposures, as well as indoor and outdoor home levels, were monitored using passive time-integrating filter badges. Monitoring extended over a one-year period (May 1987 to May 1988), with each individual providing two consecutive days of data. Information was also collected on activity patterns, household and personal characteristics, and spatial and temporal variables. This paper describes the study design, summarizes the sample characteristics and representativeness, and presents the distribution of personal, indoor, and outdoor NO2 concentrations recorded by the monitors. Over the entire sample, median personal and outdoor levels were 35 ppb; median indoor levels were 24 ppb. Personal exposures for those in homes with gas ranges with pilot lights average 10 ppb greater than those with electric ranges, and 4 ppb greater than those with gas ranges without pilot lights. Forty percent of the variation in indoor concentrations is explained by outdoor levels; 59 percent of the variation in personal exposures is explained by indoor levels; and 48 percent of the variation in personal exposures is explained by outdoor levels.

Using longitudinal data to understand children's activity patterns in an exposure context: Data from the Kanawha county health study

Abstract An important component of assessing the levels, the sources, and the health effects of childrens exposure to air pollution is understanding how and where members of this sensitive population spend their time. There are, however, few data bases that allow the documentation of the day-to-day nature of childrens activities. Of particular concern is whether the one-day snapshots provided by time/activity diaries typically used in exposure studies represent the actual temporal and spatial extent of childrens activities. As part of a community health study, longitudinal data on childrens time/activity patterns were recently collected. A respiratory health status and gender stratified sample of 90 children kept daily diaries over two-week periods during both the summer and the fall. This paper first presents baseline information of childrens activity patterns: the sample distribution of time spent in each of five microenvironments (travel, outdoor, at school, at home, and inside other locations) and the daily temporal pattern of activities. The consistent patterns of children on school days suggest that for most days we can accurately predict childrens locations by time of day. The second part of the analysis shows that there is both high child-to-child variation in the average time spent in each microenvironment, even after controlling for gender and respiratory health status, and strong temporal variability in activity patterns within a child over time, even after controlling for school days versus nonschool days.

A study of respiratory illnesses in infants and nitrogen dioxide exposure

Toxicologic and epidemiologic studies have elevated concern that exposure to nitrogen dioxide (NO2) in outdoor and indoor air may increase the frequency and severity of respiratory infections. We have developed and implemented a prospective cohort study to test the hypothesis that exposure to NO2 increases the incidence and severity of respiratory infections during the first 18 mo of life. This study, which was based on extensive pilot research, was designed to address the potential limitations of misclassification, confounding, and inadequate power. Enrollment of 1,315 subjects has been completed. This paper reviews the methods used in the study, characteristics of the enrolled subjects, NO2 concentrations in the homes of study participants, and rates of illness occurrence.

An examination of the intra-SMSA distribution of carbon monoxide exposure

Although fixed-site monitoring data have been used to estimate the spatial pattern of human exposure, the intra-urban distribution of actual exposure has not been documented. This paper used the data collected during the Environmental Protection Agencys (EPA) field investigation of personal exposure to carbon monoxide (CO) to investigate the nature of the distribution of CO with respect to residential location in the Washington, D.C. SMSA. Dot-distribution maps and analysis of variance were used to document the spatial pattern of individual-level in-home CO concentrations. The results show sampled individuals living in the SMSA center are exposed to statistically significantly higher levels of CO than are those living in the suburbs. The most important implications of this work are for exposure modeling. Further investigation is needed to determine whether incorporation of a geographic component will improve exposure prediction.