Impact of Mosquito-Repellent Incense Emissions and Aging Processes in the Indoor Environment

Mosquito-repellent incense (MRI) combustion represents a globally prevalent source of indoor air pollution, generating prolonged emissions of fine particulate matter (PM), volatile organic compounds (VOCs), and pesticides. Despite their widespread use, primary emissions from MRI burning remain insufficiently characterized, and the indoor chemical aging processes of these pollutants are yet to be elucidated. Combining controlled chamber experiments and field measurements, we systematically characterized the primary emissions and ozone-driven transformations of MRI smoke. Burning one gram of MRI emits 6.3 ± 2.1 mg PM1 (particle diameter ≤1 nm) with 25 μg dimefluthrin pesticide and 8.5 ± 4.3 mg VOCs. Many VOCs are unsaturated and reactive with ozone. Upon ozone exposure, the aerosol mass concentration increased by 12% (comprising nitrates and oxygenated organics), with semivolatile and extremely low-volatility species increasing by 37 and 11%, respectively. Ozone exposure led to substantial transformation of MRI smoke, accompanied by formation of dimefluthrin derivatives and hazardous VOCs, e.g., carbonyls, amides, and isocyanates. Field experiments confirmed ozone-mediated VOC oxidation and revealed suppressed secondary aerosol formation due to competing surface interactions. These findings highlight that indoor aging processes significantly increase the complexity of MRI-derived pollutants, underscoring the necessity of incorporating multiphase chemistry into exposure assessments.