Attribution of Elevated Indoor CO2 Levels to Household Energy Consumption

It has been concerned that elevated CO2 exposure may adversely affect human health. In many low- and middle-income countries where fossil-based solid fuels are widely used household energies, the burning produces large amounts of CO2 indoors, that has received relatively little attention. Here, a large-scale multiregional field investigation in rural China using low-cost sensors was conducted to evaluate indoor CO2 dynamics in households using clean or polluting energies. Across all households, the median value of daily indoor CO2 was 624 ppm, which was higher than the model-derived regional outdoor background. Households using traditional solid fuels exhibited significantly higher indoor CO2 concentrations than those using cleaner fuels such as coals, pelletized biofuels, and electricity, with more than 20% of daily means in the former group exceeded 1000 ppm. A decomposition analysis estimated that the heating-related activity contribuated approximately 165 ppm CO2 indoor on average, accounting for about 23% of total indoor CO2 which was operationally treated as a seasonal residual. Households using natural gas showed relatively high indoor CO2 concentrations. The median concentration in natural-gas households (∼725 ppm) was statistically lower than that in raw-coal households (∼784 ppm), but the rank–biserial correlation was small (rrb = −0.09), highlighting a modest difference in magnitude. These findings reveal widespread exposure to elevated indoor CO2 in households. Also that, during clean-energy transitions, greater attention should be paid to the potential influence of gaseous fuels such as natural gas on indoor CO2 accumulation. Elevated indoor CO2 and its potential health relevance deserve further investigation in indoor air quality management and related policy discussions.