Exposure measurement
EVENTS
Smoke produced from cooking with carbon-based fuels is an indication of incomplete combustion which results in a complex mixture of particulate matter and gases. Carbon monoxide (CO) is one of the incomplete combustion products for which there existed viable, miniaturized, low cost sensors available at the time of the GRAPHSs study. As such, small, lightweight CO monitors (Lascar EL-CO-USB Data Logger, Essex, UK) were used for personal sampling among all women and infants in the study at defined time points. An initial exposure baseline assessment was done immediately after enrollment and prior to delivery of the clean stove intervention. Three additional exposure monitoring sessions were completed, initially approximately three weeks after initiation of the cooking intervention, and at two additional time points evenly spaced across the remaining expected weeks of gestation. Women and their infants both underwent postnatal exposure monitoring at months one, three and nine, for a total of 7 exposure sessions on each enrolled woman and three on each infant.At each measurement occasion, a series of 72-h personal CO exposure assessment were made. Using the Lascar monitors, CO was recorded every ten seconds in parts per million (ppm). The detection limit of the Lascar’s 10 s readings is ca. 3 ppm. In a typical indoor/outdoor household setting, the unit read zero much of the time. These readings were however not replaced since it was assumed that true exposure was likely to be close to zero when no combustion events were occurring. The averages over the multiday monitoring sessions were driven by brief time periods, typically around meal times, with very high CO concentrations (10 s to > 1000 ppm). After data cleaning, each deployment was truncated to the first 48 h to avoid having an uneven number of cooking events captured for units that did not run for the entire 72 h. Using a time-weighted average approach, prenatal average CO from the beginning of pregnancy to birth and a postnatal average CO from birth to the first birthday of the child was computed from the individual 48 h averages.