Persistent Desorption, Aging, and Secondary VOC Formation from Biomass-Burning Emissions on Indoor Surfaces

Biomass burning (BB) degrades indoor air quality both through direct emissions and via smoke sorption onto surfaces, resulting in persistent pollutant re-emission and transformation. However, the dynamics of this multiphase process remain unclear. This study investigates the re-emission, chemical aging, and secondary product formation of smoke residues on three representative indoor surfaces (glass, cotton, and gypsum). Smoke-contaminated surfaces re-emitted 120-180 distinct volatile organic compounds (VOCs). After 2 weeks of ventilation, the median emission rates of various VOCs from porous cotton and gypsum (3.3 and 4.2 μg m-2 h-1) far exceeded that from glass (0.06 μg m-2 h-1), reflecting their greater sorption capacity and longer pollutant persistence. The emission increased by factors of 7 and 4 on glass and cotton when relative humidity (RH) rose from 20% to 80%, attributed to enhanced initial sorption. Smoke-sorbed gypsum showed a strong ozone (O3) uptake coefficient ((1.6 ± 0.2) × 10-5 at 50 ppb O3, 20% RH), approximately 20 times that on glass, confirming its role as a key indoor O3 sink. Heterogeneous transformation of surface residues produced secondary VOCs, including aldehydes and carboxylic acids, further deteriorating indoor air quality. These findings demonstrate the critical and prolonged influence of surface-retained BB emissions on indoor air chemistry.