Bioethanol fireplaces as indoor pollution sources: The role of burner design and fuel type

Bioethanol fireplaces are marketed as clean and decorative heating alternatives. However, their impact on indoor air quality (IAQ) remains poorly characterised. This study investigates the indoor levels of gaseous and particulate pollutants using a bioethanol fireplace operated under realistic conditions. Two types of bioethanol fuels and two burner designs, a single-chambered (SC) and a double-chambered (DC), were tested under minimal ventilation. Concentrations of CO, NO, NO₂, CO₂, NH₃, N₂O, C₂H₆O, total volatile organic compounds (TVOCs), and carbonyl compounds were measured, while particulate matter (PM₁₀) was characterised chemically and toxicologically. Combustion of both fuels led to substantial increases in indoor pollutant concentrations compared to background levels. Indoors, maximum average CO levels reached 5.67 µg m^-3, NO 0.33 µg m^-3, NO₂ 0.85 µg m^-3 and TVOCs exceeded 1400 µg m^-3. Acetaldehyde and formaldehyde were the dominant carbonyls, with the latter frequently surpassing the WHO guideline value along with NO₂. Compared with traditional wood combustion, bioethanol combustion produced relatively higher indoor concentrations of nitrogen oxides, acetaldehyde, and formaldehyde. Average PM₁₀ concentrations ranged from 31.5 to 173 µg m^-3, with higher indoor concentrations for the DC burner and Fuel 2. PM₁₀ samples were enriched in bromine, ammonium and nitrate during combustion, and exhibited elevated oxidative potential. Differences in indoor pollutant levels and oxidative potential were observed depending on the burner design, fuel type and initial fuel load. These results demonstrate that flueless bioethanol fireplaces can markedly deteriorate IAQ, underscoring the need for performance standards, improved fuel formulations, and adequate ventilation to mitigate exposure risks associated with their use.