Indoor Coal Combustion for Heating Exacerbates CO2Exposure Approaching Harmful Levels

Nearly three billion people still rely on traditional solid fuels for daily activities, which emit large amounts of many hazardous air pollutants, as well as CO2 indoors. Indoor CO2 should not be just a proxy for air exchange, as elevated CO2 exposure could pose a variety of direct risks to human health, including mental and physiological diseases. Here, we evaluated indoor CO2 levels in rural coal-use households to test the hypothesis that the incremental CO2 associated with indoor coal use may result in chronic exposure close to harmful levels. Significantly elevated daily concentrations of indoor CO2 were observed of 750 ± 230 ppm indoors in comparison with that outdoors. More than 12% of the daily data exceeded the threshold of 1000 ppm, with a maximum of up to 2960 ppm, at which level a variety of health risks can potentially occur. Internal sources contributed ∼280 ppm to indoor CO2 exposure during the heating period, wherein ∼50% was from coal combustion. The study sheds light on the crucial role of the widespread exposure to indoor CO2 and collaboration efforts in considering CO2 as an indoor air pollutant.