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.