Indoor new particle formation (NPF) associated with the oxidation of terpenes can be an important source of ultrafine particles in buildings. While observations of NPF events have been made in indoor environments, there have been no prior reports of size-resolved growth rates (GRs) down to molecular length scales. GRs inform how rapidly newly formed particles grow into larger sizes via condensation of low volatility vapors and provide a basis for direct comparisons of NPF intensity in indoor and outdoor atmospheres. This study characterizes size-resolved GRs of secondary organic aerosol due to the ozonolysis of terpenes released from household products. Indoor NPF experiments were conducted in a mechanically ventilated residential building. Electrical mobility-based particle number size distributions down to 1.75 nm were measured with a novel particle size magnifier-scanning mobility particle sizer (PSMPS). Terpene concentrations were measured via a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). A variety of terpene-based products were evaluated, including air fresheners, cleaning agents, personal care products, citrus fruit, and aromatherapy products. Indoor use of terpene-based products initiated NPF events under low ozone concentrations (&lt;25 ppb). High terpene concentrations (&gt;50 ppb) drove rapid aerosol growth, with GRs increasing with particle size from 1.75 to 25 nm: GR1.75-3nm~1.5-30 nm/h, GR3-10nm~50-250 nm/h, GR10-25nm~175-1000+ nm/h. Notably, indoor GRs were significantly greater than those reported for outdoor environments across all size fractions, likely due to the formation of a large pool of low volatility vapor that facilitated condensational growth. GRs were influenced by the type of terpene-based product and the building ventilation rate.

Observations of rapid organic aerosol nucleation and growth in the indoor atmosphere

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