Impact of mitigation measures to improve home indoor air quality in Kathmandu, Nepal

Air purifiers (APs) and home sealing are interventions used to help protect U.S. diplomats against particle pollution in the home when working in polluted cities. We investigated the effect of these interventions on home indoor and personal PM2.5 exposure in Kathmandu, Nepal. Twenty-one participants underwent repeated 48 hour personal monitoring before and after intervention. We analyzed these measurements by microenvironment. Indoor-outdoor ratios (I/O) using the home indoor PM2.5 values were calculated in order to assess the air filtration capacity at home in light of increasing outdoor PM2.5 post-intervention. To quantify the effect of intervention on home indoor PM2.5, we conducted a meta-analysis of the results of dwelling-by-dwelling regression of indoor-on-outdoor (I/O) PM2.5 concentrations. On average, adding high-capacity APs and home sealing led to a 15% decrease in PM2.5 measured at home, excluding cooking periods, with a mean (standard deviation) of 7.5 (6.4) μg m−3 pre- to 6.4 (8.1) μg m−3 post-intervention despite a 57% increase in outdoor PM2.5, from 43.8 (30.8) μg m−3 pre- to 68.9 (40.7) μg m−3 post-intervention. Overall mean personal exposure fell by 36% from 15.2 (10.6) μg m−3 to 9.8 (8.7) μg m−3. I/O ratios decreased as outdoor PM2.5 strata increased; when outdoor PM2.5 < 25 μg m−3 the I/O decreased from 0.38 pre- to 0.12 post-intervention and when outdoor PM2.5 was 101–200 μg m−3 the I/O decreased from 0.12 pre- to 0.07 post-intervention. The mean regression slope of indoor-on-outdoor PM2.5 decreased from 0.13 (95% CI 0.09, 0.17) in pre-intervention dwellings to 0.07 (0.04, 0.10) post-intervention. I/O ratios showed a weak negative (not statistically significant) inverse association with air changes per hour at home. In the high pollution environment of Kathmandu, APs with home sealing provide substantial protection against ambient PM2.5 in the home environment, including during periods when outdoor PM2.5 concentration was above 100 μg m−3.