Real-Time Measurements of Botanical Disinfectant Emissions, Transformations, and Multiphase Inhalation Exposures in Buildings

Thymol-based botanical disinfectants have emerged as natural alternatives to traditional chemical disinfectants given their effectiveness as antimicrobial pesticides and ability to inactivate SARS-CoV-2. This study investigates the impact of botanical disinfectants on indoor air chemistry and human exposure. Controlled surface disinfection experiments were conducted in a mechanically ventilated zero-energy tiny house laboratory. Volatile organic compounds (VOCs) and aerosol size distributions were measured in real-time (1 Hz) with a proton transfer reaction time-of-flight mass spectrometer and a high-resolution electrical low-pressure impactor, respectively. Botanical disinfectant spray and wipe products drove sudden changes in the chemical composition of indoor air. Mixing ratios of monoterpenes (C 10 H 16 ) and monoterpenoids (C 10 H 14 O, C 10 H 16 O, C 10 H 18 O, and C 10 H 20 O) increased suddenly during the disinfection events (10 –1 to 10 2 ppb) and exhibited volatility-dependent temporal emission profiles. VOC emission factors ranged from 10 0 to 10 4 μg g –1, and thymol intake fractions ranged from 6 to 7 × 10 3 ppm. Rapid new particle formation events were observed due to ozonolysis of monoterpenes and monoterpenoids, increasing sub-100 nm particle number concentrations by 10 4 to 10 5 cm –3 . Botanical disinfectant sprays initiated multiphase inhalation exposure to VOCs, secondary organic aerosol, and sub-10 μm droplets, with large deposited doses in each respiratory tract region associated with the latter two.