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Exposure to particulate matter (PM) air pollution has been shown to exacerbate children's asthma, but the exposure sources and temporal characteristics are still under study. Children's exposure to PM is likely to involve both combustion-related ambient PM and PM related to a child's activity in various indoor and outdoor microenvironments. Among 19 children with asthma, 9-17 years of age, we examined the relationship of temporal changes in percent predicted forced expiratory volume in 1 sec (FEV 1 ) to personal continuous PM exposure and to 24-hr average gravimetric PM mass measured at home and central sites. Subjects were followed for 2 weeks during either the fall of 1999 or the spring of 2000, in a southern California region affected by transported air pollution. FEV 1 was measured by subjects in the morning, afternoon, and evening. Exposure measurements included continuous PM using a passive nephelometer carried by subjects; indoor, outdoor home, and central-site 24-hr gravimetric PM 2.5 (PM of aerodynamic diameter < 2.5 µm) and PM 10 ; and central-site hourly PM 10 , nitrogen dioxide, and ozone. Data were analyzed with linear mixed models controlling for within-subject autocorrelation, FEV 1 maneuver time, and exposure period. We found inverse associations of FEV 1 with increasing PM exposure during the 24 hr before the FEV 1 maneuver and with increasing multiday PM averages. Deficits in percent predicted FEV 1 (95% confidence interval) for given PM interquartile ranges measured during the preceding 24-hr were as follows: 128 µg/m 3 1-hr maximum personal PM, -6.0% (

Recent experimental findings in animals and humans indicate adverse respiratory effects from short -term exposures to particulate air pollutants, especially in sensitive subpopulations such as asthmatics. The relationship between air pollution and asthma has mainly been determined using particulate matter (PM) measurements from central sites. Validated tools are needed to assess exposures most relevant to health effects. Recently, a personal passive particulate sampler ( personal Data -RAM, pDR, MIE Inc., Bedford, MA ) has become available for studying personal exposures to PM with time resolution at 1 min. The pDR measures light scatter from PM in the 0.1 ± 10 M range, the significant range for health effects. In order to assess the ability of the pDR in predicting gravimetric mass, pDRs were collocated with PM 2.5 and PM 10 Harvard Impactors ( HI ) inside and outside nine homes of asthmatic children and at an outdoor central Air Pollution Control District site. Results are presented of comparisons between the HI samplers and the pDR in various modes of operation: passive, active, and active with a heated inlet. When used outdoors at fixed sites the pDR readings exhibit interference from high relative humidity ( RH ) unless operated with a method for drying inlet air such as a heater, or if readings at times of high RH are adjusted. The pDR correlates more highly with the HI PM 2.5 than with the HI PM 10 ( r 2 = 0.66 vs. 0.13 for outdoors, r 2 = 0.42 vs. 0.20 for indoors ) . The pDR appears to be a useful tool for an epidemiologic study that aims to examine the relationship between health outcomes and personal exposure to peaks in PM. Journal of Exposure Analysis and Environmental Epidemiology ( 2000 ) 10, 437 ± 445.

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