Emission of Carbon Monoxide (CO) and Carbon Dioxide (CO2) from Household Solid Fuels Burning Practices: Development of Real World Emission Factor and Removal Methods

Solid fuels such as fuelwood (FW), coal balls (CB), dung cake (DC), and agricultural residue (AR) are widely used for domestic heating and cooking in developing countries, particularly in rural and peri-urban regions. Combustion of these fuels is a major source of carbon-based gaseous emissions, notably carbon monoxide (CO) and carbon dioxide (CO₂), contributing to indoor air pollution, adverse health effects, and climate change. The emission characteristics of these gases are strongly influenced by fuel moisture content, elemental composition, and inorganic constituents. This study presents the development of emission factors (EFs) for CO and CO₂ from commonly used solid fuels and evaluates materials-based mitigation strategies using a laboratory-designed fixed-bed reactor system with a combustion chamber simulating real-world burning conditions.

Fuel samples were collected from representative domestic sources, air-dried, pulverized, and homogenized prior to analysis. Moisture content was determined gravimetrically by oven drying at 105 °C. Ultimate analysis of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) was performed using a CHNS/O elemental analyzer, while anionic and cationic species were quantified using ion chromatography. Combustion experiments for emission factor development were conducted in a custom-designed fixed-bed reactor equipped with a controlled burning chamber to simulate domestic heating conditions. The reactor enabled stable combustion, controlled airflow, and downstream integration of mitigation materials for post-combustion treatment of exhaust gases. It also includes real-gas cylinders to generate the gas mixture representing smoke.

The results revealed notable variability in fuel composition and emission behavior. FW exhibited relatively efficient combustion with lower CO emissions, while DC, with higher moisture and lower carbon content, produced higher CO levels. CB showed high CO emissions despite its carbon content, whereas AR displayed intermediate emission characteristics. Elevated levels of alkali metals and anions, particularly in DC, were associated with reduced combustion efficiency and increased CO formation.

The hazards of these gases demands for removal. In this study, removal experiments were carried out by integrating advanced functional materials into the exhaust section of the fixed-bed reactor. Porous and nanostructured materials such as graphene-based materials, biochar, graphitic carbon nitride (g-C₃N₄), zeolites, metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and silica-based materials were evaluated for CO oxidation and CO₂ capture. Material characterization using Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed high specific surface area, well-developed porous structures, and the presence of reactive surface functional groups, which directly enhance adsorption and catalytic conversion of carbonaceous gases.

Overall, the study demonstrates that fuel chemical composition and combustion conditions strongly influence CO and CO₂ emission factors from domestic heating activities. The integration of a designed fixed-bed reactor with a burning chamber and advanced materials-based mitigation strategies provides a robust experimental framework for reducing carbon-based emissions and improving air quality in regions dependent on traditional solid fuels.