Assessing Exposure to Household Air Pollution: A Systematic Review and Pooled Analysis of Carbon Monoxide as a Surrogate Measure of Particulate Matter

Abstract

Background: Household air pollution from solid fuel burning is a leading contributor to disease burden globally. Fine particulate matter (PM_2.5) 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. https://doi.org/10.1289/EHP767.

Figure 1.

Flow diagram of systematic search of literature for review.

Figure 2.

Paired personal ${\text{PM}}_{2.5}$ and personal CO exposure measurements for (a) all observations combined from nine studies and for (b–i) individual studies. One outlying data point for Tanzania (CO: 25.2 ppm, ${\text{PM}}_{2.5}$: $42.9{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), one for Peru (CO: 25.2 ppm, ${\text{PM}}_{2.5}$: $42.9{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), two for Guatemala (CO: 18.5 ppm, ${\text{PM}}_{2.5}$: $284{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; CO: 23.6 ppm, ${\text{PM}}_{2.5}$: $\mathrm{1,843}{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), and two for India (CO: 14.7 ppm, ${\text{PM}}_{2.5}$: $\mathrm{1,226}{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; CO: 9.5 ppm, ${\text{PM}}_{2.5}$: $\mathrm{1,243}{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$) are not pictured to improve data visualization. 2h has an expanded CO concentration range along the horizontal axis.

Figure 3.

Natural log-transformed ${\text{PM}}_{2.5}$ personal exposures versus natural log-transformed CO personal exposures plotted for nine unique studies. The Spearman correlation ($\pm 95\%$ confidence intervals) for all observations ($n=714\text{pairs}$) is presented at the bottom left of the figure.

Figure 4.

Comparison of estimates of the slope of $\ln \left({\text{PM}}_{2.5}\right)$ on $\ln \left(\text{CO}\right)$ ($\pm 95\%$ confidence intervals) for personal exposures using univariate and multivariate linear regression models for the full data set and stratified by subsets of the data. The $R^2$ values and root mean squared error (RMSE) for each model are reported to the right of the plotted $\ln \left(\text{CO}\right)$ slope. Note: CI, confidence interval; RMSE, root mean squared error.

Figure 5.

Paired personal and cooking area ${\text{PM}}_{2.5}$ and CO (24- or 48-hr integrated concentrations) for (a) China (Ni et al. 2016), (b) Honduras (Peel JL, written and oral communication, spring 2016), (c) The Gambia (Dionisio et al. 2012), (d) Peru (St. Helen et al. 2015), and Peru (e) pre- and (f) postintervention (Fitzgerald et al. 2012). The $R^2$ and slope of the $\ln \left({\text{PM}}_{2.5}\right)-\ln \left(\text{CO}\right)$ relationship is shown for cooking area measurements (blue) and personal exposures (black).