IVL Swedish Environmental Research Institute

Nanocluster aerosols (NCAs, particles <3 nm) are important players in drivingclimate feedbacks and processes that impact human health. This study reports, for the first time, NCA formation when gas-phase ozone reacts with human surfaces. In an occupied climatecontrolledchamber, we detected NCA only when ozone was present.

NCA emissions weredependent on clothing coverage, occupant age, air temperature, and humidity. Ozone-initiated chemistry with human skin lipids (particularly their primary surface reaction products) is thekey mechanism driving NCA emissions, as evidenced by positive correlations with squalene in human skin wipe samples and known gaseous products from ozonolysis of skin lipids. Oxidation by OH radicals, autoxidation reactions, and human-emitted NH3 may also play a role in NCA formation. Such chemical processesare anticipated to generate aerosols of the smallest size (1.18−1.55 nm), whereas larger clusters result from subsequent growth of the smaller aerosols. This study shows that whenever we encounter ozone indoors, where we spend most of our lives, NCAs will be produced in the air around us.