Ozone Reactions with Indoor Surfaces Soiled by Human Skin Oil are Impacted by Manner of Soiling, Relative Humidity, and Air Change Rate.

Human skin oil transferred to indoor surfaces is an important ozone sink and source of oxidation products, yet the effects of soiling mode and environmental conditions on this chemistry remain poorly understood. We examined ozone-initiated reactions on glass plates soiled by long-term natural accumulation, fresh squame deposition, or direct dermal contact at 20% or 70% relative humidity, air change rates of 6 or 12 h-1, and 42 ± 5 ppb ozone. Gas-phase products were quantified by PTR-ToF-MS, and surface residues by GC-MS. Ozone exposure consumed 22-98% of the squalene, depending on the soiling mode. Major gas-phase products included acetone, 4-oxopentanal (4OPA), and 6-methyl-5-hepten-2-one (6MHO); condensed-phase products included geranyl acetone (GA) and C22-aldehyde (4,9,13,17-tetramethyl-4,8,12,16-octadecatetraenal). Elevated relative humidity and lower air change rates enhanced ozone uptake and gas-phase product formation. Gas-phase product yields depended on relative humidity but not systematically on ventilation rate, whereas surface-bound product yields showed no systematic dependence on either parameter. Plates soiled by direct contact produced more than an order of magnitude higher volatile product mixing ratios than plates soiled with freshly deposited squames. These results show that soiling mode and environmental conditions strongly influence ozone-driven chemistry on skin-oil-contaminated indoor surfaces.