Yearlong study of indoor VOC variability: insights into spatial, temporal, and contextual dynamics of indoor VOC exposure†

Volatile organic compounds (VOCs) are released from many sources indoors, with ingress of outdoor air being an additional source of these species indoors. We report indoor VOC concentrations for 124 homes in Bradford in the UK, collected between March 2023 and April 2024. Whole air samples were collected over 72 hours in the main living area of the home. Total VOC (TVOC) concentrations in the homes were highly variable, ranging from 100 μg m⁻³ to >8000 μg m⁻³ (median concentration ∼1000 μg m⁻³). Acetaldehyde and 1,3-butadiene concentrations in >75% of homes were found to be in exceedance of the 1 in 1 000 000 lifetime cancer risk threshold. Higher concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) as well as trimethylbenzenes were found in urban houses (summed xylene median 2.35 μg m⁻³) compared to rural homes (summed xylene median 1.22 μg m⁻³, p-value = 0.02), driven by ingress of elevated outdoor BTEX and trimethylbenzenes (outdoor urban BTEX median 1.69 μg m⁻³, outdoor rural BTEX median 0.78 μg m⁻³). Inferred air change rate (ACR) exhibited a degree of seasonality, with average ACR varying between median values of 1.2 h⁻¹ in the summer and 0.70 h⁻¹ in winter. Time-averaged emission rate data provided additional insight compared to measured concentrations, such as seasonal variability, with highest total VOC time-averaged emission rates occurring in summer months (median 51 953 μg h⁻¹), potentially a product of both increased occupancy times during school holidays as well as off-gassing of VOCs from surfaces. This comprehensive analysis underscores the critical role of seasonal, spatial, and contextual factors in shaping indoor VOC exposure, as well as potential health risks associated with consistently elevated concentrations of specific VOCs.