- Full (HTML) - Related EHP Articles -

Michael Lipsett,¹ Susan Hurley,² and Bart Ostro¹

¹California Office of Environmental Health Hazard Assessment, Berkeley, California 94704 USA; ²California Department of Health Services, Berkeley, California 94704 USA

Abstract

During the winters of 1986-1987 through 1991-1992, rainfall throughout much of Northern California was subnormal, resulting in intermittent accumulation of air pollution, much of which was attributable to residential wood combustion (RWC) . This investigation examined whether there was a relationship between ambient air pollution in Santa Clara County, California and emergency room visits for asthma during the winters of 1988-1989 through 1991-1992. Emergency room (ER) records from three acute-care hospitals were abstracted to compile daily visits for asthma and a control diagnosis (gastroenteritis) for 3-month periods during each winter. Air monitoring data included daily coefficient of haze (COH) and every-other-day particulate matter with aerodynamic diameter equal to or less than 10 microns (PM₁₀, 24-hr average) , as well as hourly nitrogen dioxide and ozone concentrations. Daily COH measurements were used to predict values for missing days of PM₁₀ to develop a complete PM₁₀ time series. Daily data were also obtained for temperature, precipitation, and relative humidity. In time-series analyses using Poisson regression, consistent relationships were found between ER visits for asthma and PM₁₀. Same-day nitrogen dioxide concentrations were also associated with asthma ER visits, while ozone was not. Because there was a significant interaction between PM₁₀ and minimum temperature in this data set, estimates of relative risks (RRs) for PM₁₀-associated asthma ER visits were temperature-dependent. A 60 g/m³ change in PM₁₀ (2-day lag) corresponded to RRs of 1.43 (95% CI = 1.18-1.69) at 20°F, representing the low end of the temperature distribution, 1.27 (95% CI = 1.13-1.42) at 30°F, and 1.11 (95% CI = 1.03-1.19) at 41°F, the mean of the observed minimum temperatures. ER visits for gastroenteritis were not significantly associated with any pollutant variable. Several sensitivity analyses, including the use of robust regressions and of nonparametric methods for fitting time trends and temperature effects in the data, supported these findings. These results demonstrate an association between ambient wintertime PM₁₀ and exacerbations of asthma in an area where one of the principal sources of PM₁₀ is RWC. Key words: asthma, emergency room visits, epidemiology, particulate air pollution, wood smoke. Environ Health Perspect 105:216-222 (1997)

Address correspondence to M. Lipsett, California Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, 2151 Berkeley Way, Annex 11, Berkeley, CA 94704 USA.

The authors would like to acknowledge the assistance of Constance Heye in abstracting the emergency room data, the staff of the Bay Area Air Quality Management District for providing the air monitoring data, David Fairley, Bay Area Air Quality Management District, and Lianne Sheppard, University of Washington, for helpful comments on earlier drafts. The contents and opinions expressed in this manuscript are those of the authors and do not represent the official position of the Office of Environmental Health Hazard Assessment, the California Environmental Protection Agency, or the State of California. This paper was presented in part at an International Specialty Conference on Particulate Matter, Pittsburgh, PA, sponsored by the Air & Waste Management Association, April 1995, and at the annual meeting of the American Thoracic Society, Seattle WA, May 1995.

Received 11 June 1996 ; accepted 13 November 1996.