Real-Time Characterization of Airborne Nanoparticle and Volatile Organic Compound Emissions from Dry Shampoo Products in a Residential Test House

Personal care products (PCPs) and hair care products (HCPs) are well-established sources of indoor airborne nanoparticles and volatile organic compounds (VOCs), yet emissions from propellant-based aerosol HCPs, including the rapidly growing class of dry shampoos, remain poorly characterized in residential use scenarios. Here, we present real-time, breathing zone measurements of particle- and gas-phase emissions during the use of five commercially available propellant-based aerosol HCPs (four dry shampoos and one hair shine spray) in a full-scale, mechanically ventilated residential test house. Particle aerodynamic size distributions from 6 nm to 10 µm were resolved at 1 Hz with a high-resolution electrical low-pressure impactor (HR-ELPI+), enabling continuous tracking of nanoparticle emissions, growth, and decay. Total VOC (TVOC) mixing ratios were monitored in parallel using a photoionization detector (PID) at 5 s resolution. Across 14 well-mixed experiments, dry shampoo application generated breathing zone size-integrated nanoparticle number concentrations of 10 3 –10 4 cm -3 with peaks reaching ~10 5 cm -3 . Sub-100 nm nanoparticles, on average, accounted for ~92% of total number concentrations, and over half of the detected nanoparticles had aerodynamic diameters below 20 nm. Concurrent peak TVOC mixing ratios reached up to ~5 × 10 3 ppb. Under non-mixed conditions representative of small bathroom enclosures, breathing zone peak number concentrations reached up to ~8 × 10 5 cm -3 and TVOC mixing ratios reached up to ~2 × 10 4 ppb. These findings identify dry shampoo use as a significant, previously underexamined indoor source of breathing zone nanoparticles and co-emitted VOCs, with direct implications for indoor air quality and inhalation exposure assessment.