Effects of Fuel Moisture Content on Emissions from a Rocket-Elbow Cookstove

Exposure to air pollution from solid-fuel cookstoves is a leading risk factor for premature death; however, the effect of fuel moisture content on air pollutant emissions from solid-fuel cookstoves remains poorly constrained. The objective of this work was to characterize emissions from a rocket-elbow cookstove burning wood at three different moisture levels (5%, 15%, and 25% on a dry mass basis). Emissions of carbon dioxide (CO₂), carbon monoxide (CO), methane, fine particulate matter (PM_2.5), PM_2.5 elemental carbon (EC), PM_2.5 organic carbon, formaldehyde, acetaldehyde, benzene, toluene, ethylbenzene, and xylenes were measured. Emission factors (EFs; g·MJ_delivered^-1) for all pollutants, except CO₂ and EC, increased with increasing fuel moisture content: CO EFs increased by 84%, PM_2.5 EFs increased by 149%, formaldehyde EFs increased by 216%, and benzene EFs increased by 82%. Both modified combustion efficiency and the temperature at the combustion chamber exit decreased with increasing fuel moisture, suggesting that the energy required to vaporize water in the fuel led to lower temperatures in the combustion chamber and lower gas-phase oxidation rates. These results illustrate that changes in fuel equilibrium moisture content could cause EFs for pollutants such as PM_2.5 to vary by a factor of 2 or more across different geographic regions.