Total OH reactivity measurements of indoor emissions from hair care products

The impact of emissions from human activities on indoor and outdoor air quality is not fully understood. Recent outdoor measurements have suggested that emissions of volatile chemical products (VCPs), including personal care products, cleaning agents, and pesticides, are now a significant source of volatile organic compounds (VOCs) that can contribute to the production of ozone and secondary organic aerosols in urban areas. Recent measurements of total hydroxyl radical (OH) reactivity in urban areas are often greater than that predicted by current models, and it has been suggested that unmeasured VCPs may account for the missing reactivity. Additional measurements of the reactivity of VCP emissions in indoor environments are needed to improve our understanding of the impact of these indoor emissions on outdoor air quality.

The Total OH Loss rate Method (TOHLM) technique was used to measure the total OH reactivity of indoor emissions from the use of hair care products in a mechanically ventilated zero-energy tiny house laboratory as part of the zEDGE-iRACE (zero Energy Design Guidance for Engineers-indoor Radical and Aerosol Chemistry Experiment) in 2021. A proton transfer reaction-mass spectrometer (PTR-MS) was used to characterize the concentrations of VOCs, including siloxanes, in real-time (1 Hz). Various hair care products and hair styling techniques were tested, including hair straightening, curling, waving, and oiling. The OH reactivity increased during the application period of the hair care products from 5 - 10 s-1 to about 20 - 30 s-1 and decayed for 20 - 30 minutes. The OH reactivity was dominated by the emissions of siloxanes, monoterpenes, and oxygenated VOCs. Significant missing OH reactivity was observed during the application of hair care products. Potential reasons for the discrepancy between the measured and calculated OH reactivity will be discussed.