Abstract
Traditional wood stoves emit high levels of particulate matter ≤ 2.5 μm (PM(2.5)), prompting the development of improved models to reduce emissions. However, these stoves may unintentionally increase ultrafine particle ≤ 100 nm (UFP) emissions, which can penetrate biological barriers and pose health risks. This study evaluates the impacts of four solid fuel types on indoor air quality (IAQ) in five non-smoking households in Guildford, United Kingdom, using different wood stoves (eco-design, multifuel eco-design, clear skies stage (v), and open fireplace) during winter. Indoor UFP, PM(10), PM(2.5), black carbon (BC), and carbon monoxide (CO) levels were measured using handheld monitors in living areas. Fuel type, room volume, stove type, and burning duration significantly influenced IAQ, exacerbated by inadequate ventilation. Open fireplaces had the highest exposure levels, followed by multifuel eco-design, eco-design, and clear skies stage (v) stoves. During burning periods, median (interquartile range) indoor pollutant concentrations were UFP: 3.6 (5.8) ×10⁴ # cm⁻³, PM(2.5): 38.4 (65.5) µg m⁻³, PM(10): 89.6 (89.0) µg m⁻³, and BC: 1.7 (3.6) µg m⁻³ for open fireplaces. Among improved stoves, multifuel eco-design had the highest exposure; UFP: 2.2 (4.9) ×10⁴ # cm⁻³, PM(2.5): 14.2 (16.9) µg m⁻³, PM(10): 37.9 (45.9) µg m⁻³, and BC: 1.5 (2.3) µg m⁻³ followed by eco-design, and clear skies stage (v) stoves. Wood briquettes produced the highest pollutant levels, followed by smokeless coal, kiln-dried wood, and seasoned wood. Burning manufactured fuels (wood briquettes) increased PM(2.5) and UFP by 4- and 1.5-times, respectively, compared to seasoned wood. The mean CO concentration for open fireplaces was 3.1 ppm, below the World Health Organisation's (WHO) 24-hour exposure limit guideline (3.49 ppm). Smaller rooms (< 40 m³) with longer burning durations increased exposure by 2- and 3-times compared to larger rooms (> 50 m³). Low air changes per hour (ACH) (< 1.2 h⁻¹) contributed to pollutant accumulation. Our findings indicate that residential wood burning significantly increases short-term exposure to UFPs, PM(2.5), BC, and CO, posing potential health risks. These results underscore the need for health-focused strategies when considering wood burning for domestic heating.