Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments

Cigarette smoke is an important source of particles and gases in the indoor environment. In this work, aging of side-stream cigarette smoke was studied in an environmental chamber via exposure to ozone (O₃), hydroxyl radicals (OH) and indoor fluorescent lights. Aerosol mass concentrations increased by 13-18% upon exposure to 15 ppb O₃ and by 8-42% upon exposure to 0.45 ppt OH. Ultrafine particle (UFP) formation was observed during all ozone experiments, regardless of the primary smoke aerosol concentration (185-1950 μg m^-3). During OH oxidation, however, UFP formed only when the primary particle concentration was relatively low (<130 μg m^-3) and the OH concentration was high (∼1.1 × 10⁷ molecules cm^-3). Online aerosol composition measurements show that oxygen- and nitrogen- containing species were formed during oxidation. Gas phase oxidation of NO to NO₂ occurred during fluorescent light exposure, but neither primary particle growth nor UFP formation were observed. Overall, exposure of cigarette smoke to ozone will likely lead to UFP formation in indoor environments. On the other hand, UPF formation via OH oxidation will only occur when OH concentrations are high (∼10⁷ molecules cm^-3), and is therefore less likely to have an impact on indoor aerosol associated with cigarette smoke.