CO₂ exposure, ventilation, thermal comfort and health risks in low-income home kitchens of twelve global cities

In-kitchen air pollution is a leading environmental issue, attributable to extensive cooking, poor ventilation and the use of polluting fuels. We carried out a week-long monitoring of CO₂, temperature and relative humidity (RH) in five low-income residential kitchens of 12 global cities (Dhaka, Chennai, Nanjing, Medellín, São Paulo, Cairo, Sulaymaniyah, Addis Ababa, Nairobi, Blantyre, Akure and Dar-es-Salaam). During cooking, the average in-kitchen CO₂ concentrations were 22.2% higher than the daily indoor average. Also, the highest CO₂ was observed for NV_d (natural ventilation-door only; 711 ± 302 ppm), followed by NV_dw (natural ventilation-door + window; 690 ± 319 ppm) and DV_mn (dual ventilation-mechanical + natural; 677 ± 219 ppm). Using LPG and electric appliances during cooking exhibited 32.2% less CO₂ than kerosene. Larger kitchens (46–120 m³) evinced 28% and 20% less CO₂ than medium (16–45 m³) and small (4–15 m³) ones, respectively. In-kitchen CO₂ with >2 occupants during cooking was 7% higher than that with one occupant. 87% of total kitchens exceeded the ASHRAE standard (RH >40%, temperature >23 °C) for thermal comfort. Considering the ventilation type, both the ACH (air change rate per hour) and ventilation rate followed the order: NV_dw > NV_d > DV_mn, while the trend for weekly average CO₂ concentration was NV_d > DV_mn > NV_dw. Larger kitchens presented 22% and 28% less ACH, and 82% and 190% higher ventilation rate than medium- and small-volume ones, respectively. Forty-three percent kitchens had ACH <3 h⁻¹ and ventilation rate <4 L/s/person, hence violated the conditions for ideal ventilation. Moreover, 10% of the Hazard Ratio values for 25% kitchens exceeded the CO₂ reference value (1000 ppm). Consequently, our findings prompted several recommendations towards improving in-kitchen ventilation and environmental conditions of low-income homes.