The contributions of emissions and spatial microenvironments to exposure to indoor air pollution from biomass combustion in Kenya

Acute and chronic respiratory diseases, which are causally linked to exposu re to indoor air pollution in developing countries, are the leading cause o f global burden of disease. Efforts to develop effective intervention strat egies and detailed quantification of the exposure-response relationship for indoor particulate matter require accurate estimates of exposure. We used continuous monitoring of indoor air pollution and individual time-activity budget data to construct detailed profiles of exposure for 345 individuals in 55 households in rural Kenya. Data for analysis were from two hundred te n 14-hour days of continuous real-time monitoring of concentrations of part iculate matter less than or equal to 10 mu m in aerodynamic diameter and th e location and activities of household members. These data were supplemente d by data on the spatial dispersion of pollution and from interviews. Young and adult women had not only the highest absolute exposure to particulate matter (2,795 and 4,838 mu g/m(3) average daily exposure concentrations, re spectively) but also the largest exposure relative to that of males in the same age group (2.5 and 4.8 times, respectively). Exposure during brief hig h-intensity emission episodes accounts for 31-61% of the total exposure of household members who take part in cooking and 0-11% for those who do not. Simple models that neglect the spatial distribution of pollution within the home, intense emission episodes, and activity patterns underestimate expos ure by 3-71% for different demographic subgroups, resulting in inaccurate a nd biased estimations. Health and intervention impact studies should theref ore consider in detail the critical role of exposure patterns, including th e short periods of intense emission, to avoid spurious assessments of risks and benefits.