Prediction of personal exposure to PM 2.5 in mother-child pairs in rural Ghana

Background Air pollution epidemiological studies usually rely on estimates of long-term exposure to air pollutants, which are difficult to ascertain. This problem is accentuated in settings where sources of personal exposure differ from those of ambient concentrations, including household air pollution environments where cooking is an important source. Objective The objective of this study was to assess the feasibility of estimating usual exposure to PM 2.5 based on short-term measurements. Methods We leveraged three types of short-term measurements from a cohort of mother-child pairs in 26 communities in rural Ghana: (A) personal exposure to PM 2.5 in mothers and age four children, ambient PM 2.5 concentrations (B) at the community level, and (C) at a central site. Baseline models were linear mixed models with a random intercept for community or for participant. Lowest root-mean-square-error (RMSE) was used to select the best-performing model. Results We analyzed 240 community-days and 251 participant-days of PM 2.5 . Medians (IQR) of PM 2.5 were 19.5 (36.5) μg/m 3 for the central site, 28.7 (41.5) μg/m 3 for the communities, 70.6 (56.9) μg/m 3 for mothers, and 80.9 (74.1) μg/m 3 for children. The ICCs (95% CI) for community ambient and personal exposure were 0.30 (0.17, 0.47) and 0.74 (0.65, 0.81) respectively. The sources of variability differed during the Harmattan season. Children’s daily exposure was best predicted by models that used community ambient compared to mother’s exposure as a predictor (log-scale RMSE: 0.165 vs 0.325). Conclusion Our results support the feasibility of predicting usual personal exposure to PM 2.5 using short-term measurements in settings where household air pollution is an important source of exposure. Our results also suggest that mother’s exposure may not be the best proxy for child’s exposure at age four.