Indoor-outdoor relationships for particulate matter: Exposure classifications and health effects

Abstract

As part of a study on the effects of indoor and outdoor air pollutants on respiratory health, measurements of indoor inhalable (PM 10) and respirable (PM 2.5) particulate matter have been collected in a sample of exposure-classified households. There was a close relationship between average indoor PM in these two size ranges, with a slope of 1.08 (PM 10 to PM 2.5), intercept of 12.5 μg/m 3 and R 2 of 88.6%. Samples collected in the same household during sequential weeks were generally closely related (R 2 of 85% for both sizes; difference was nonsignificant), although week-specific activities were important in explaining difference within some homes. The median indoor/outdoor (I/O) ratio was 0.63 for homes without reported smoking, and 1.1 for those with smoking. Corresponding mean indoor-outdoor differences were −3.6 and +13.5 μg/m 3, which was only significant for homes with smoking (p < 0.01). Indoor PM 10 over 50 μg/m 3 was associated with non-specific (annoyance) symptoms. PM 2.5 over 15 μg/m 3 was related to symptoms of acute respiratory infections (depending on age group) and to daily variability in peak flow rates (independent of age and sex). These effects may be related to environmental tobacco smoke (ETS) exposures that are correlated with the measured PM concentrations, although more specific indicators of ETS are needed to confirm this.