Assessing exposure to household air pollution: A systematic review and pooled analysis of carbon monoxide as a surrogate measure of particulate matter

BACKGROUND: Household air pollution from solid fuel burning is a leading contributor to disease burden globally. Fine particulate matter (PM) is thought to be responsible for many of these health impacts. A co-pollutant, carbon monoxide (CO) has been widely used as a surrogate measure of PM_2.5 in studies of household air pollution. OBJECTIVE: The goal was to evaluate the validity of exposure to CO as a surrogate of exposure to PM_2.5 in studies of household air pollution and the consistency of the PM_2.5 –CO relationship across different study settings and conditions. METHODS: We conducted a systematic review of studies with exposure and/or cooking area PM_2.5 and CO measurements and assembled 2,048 PM_2.5 and CO measurements from a subset of studies (18 cooking area studies and 9 personal exposure studies) retained in the systematic review. We conducted pooled multivariate analyses of PM_2.5 –CO associations, evaluating fuels, urbanicity, season, study, and CO methods as covariates and effect modifiers. RESULTS: We retained 61 of 70 studies for review, representing 27 countries. Reported PM_2.5 –CO correlations (r) were lower for personal exposure (range: 0.22–0.97; median = 0:57) than for cooking areas (range: 0.10–0.96; median = 0:71). In the pooled analyses of personal exposure and cooking area concentrations, the variation in ln(CO) explained 13% and 48% of the variation in ln(PM_2.5), respectively. CONCLUSIONS: Our results suggest that exposure to CO is not a consistently valid surrogate measure of exposure to PM_2.5. Studies measuring CO exposure as a surrogate measure of PM exposure should conduct local validation studies for different stove/fuel types and seasons.