Personal exposure to airborne particles : validity of outdoor concentrations of exposure in time series studies

This thesis describes a study of the relation between outdoor concentrations and personal exposure to particulate matter (PM) air pollution. The main objective of the study was to examine the validity of outdoor concentrations as a measure of exposure to PM in times series studies. Repeated measurements of personal and outdoor concentrations of particles smaller than 10μm (PM10) were conducted in 37 non-smoking adults and 45 children. In addition, repeated measurements of fine particles (FP; particles<3μm) were conducted in 13 children. For each subject separately, personal exposures were related to outdoor concentrations using linear regression analysis. The distributions of the individual correlation coefficients were investigated. Furthermore, the extent to which differences between personal and outdoor concentrations could be explained was studied.

Personal PM10 concentrations of both adults and children were reasonably well correlated over time with ambient PM10 concentrations. Personal FP exposures were highly correlated with ambient FP concentrations. Excluding days with exposure to environmental tobacco smoke (ETS) improved the correlations. In all cases, the medians of the individual correlation coefficients were higher than the estimated cross-sectional correlations.

Personal exposures exceeded outdoor concentrations. An important part of these differences could be attributed to exposure to ETS. For non-ETS exposed subjects, differences between personal and outdoor concentrations were relatively small for PM10 in adults and for FP in children. Personal PM10 concentrations among non-ETS exposed children, however, were still more than two times higher than ambient PM10 concentrations. An important part of this remaining difference could be attributed to high PM10 concentrations in the classrooms. Results of the analysis of the elemental composition of part of the classroom PM10 samples suggest that these high classroom concentrations were due to resuspension of coarse particles and/or suspension of soil material.

The findings of this study provide support for the use of fixed site measurements as a measure of exposure to PM in epidemiological time series studies linking the day-to-day variation in PM to the day-to-day variation in health endpoints.