Prediction of hourly microenvironmental concentrations of fine particles based on measurements obtained from the Baltimore scripted activity study

Researchers have developed a variety of computer-based models to estimate p opulation exposure to air pollution. These models typically estimate exposu res by simulating the movement of specific population groups through define d microenvironments. During the summer of 1998 and winter of 1999, research ers with the Harvard School of Public Health (HSPH) conducted a field study in Baltimore, MD, to acquire data for improving microenvironmental models. Using a special roll-around instrument system, a technician measured 1- an d 12-h pollutant concentrations while engaging in scripted sequences of act ivities typical of retirees. Each scripted activity assigned the technician to a geographic location and to a microenvironment. The technician recorde d special conditions associated with each activity (e.g., open windows, env ironmental tobacco smoke) in a real-time diary. Data on ambient pollutant l evels, temperature, and other potential explanatory factors were also colle cted. Eleven pollutants were measured by the roll-around instrument system, including particulate matter with an aerodynamic diameter less than 2.5 mu m (PM2.5), ozone, carbon monoxide, and benzene. This article presents the r esults of statistical analyses performed solely on the 1-h PM2.5 data measu red by a DustTrak monitor, which ranged from 1.5 to 444.8 mug/m(3) with a m edian value of 14.6 mug/m(3). Results of stepwise linear regression (SLR) s uggest that PM2.5 exposure is significantly increased by passive smoking, h igh ambient PM2.5 concentrations reported by fixed-site monitors, food prep aration, charcoal grills, car travel, outdoor roadside locations, and high humidity. Analysts should explicitly represent the effects of these paramet ers within any model developed to estimate population exposure to PM2.5. In a related study, a panel of volunteer retirees each carried a personal PM2 .5 monitor and a real-time diary for nominal 24-h sampling periods as they engaged in normal daily activities. A regression equation derived from SLR analysis of the scripted activity database was applied to eight subject-day s of diary data provided by the volunteer seniors to produce estimates of P M2.5 exposure for each event documented in each diary. The event-specific e xposure estimates were then averaged over all events in each sampling perio d to produce nominal 24-h average exposure estimates. The absolute differen ce between the estimate obtained from the regression equation and the corre sponding personal monitor measurement averaged 13%. The fixed-site monitors generally provided poorer estimates of exposure; the absolute differences for the Old Town and Clifton Park monitors averaged 26.7% and 19.5%, respec tively, of the personal monitor values.