AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Seasonal and Regional Variations of Indoor Organic Aerosol Water Content, Phase State, and Temperature-Based Partitioning
BRYAN CUMMINGS, Manabu Shiraiwa, Peter DeCarlo, Michael Waring, Drexel University
Abstract Number: 468 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Gradients in temperature and relative humidity (RH) arising from outdoor-to-indoor air transport impact organic aerosol (OA) water content, phase state, and gas-to-particle partitioning. We explored these parameter impacts using an indoor 2D-VBS aerosol chemistry model that predicts indoor OA concentration with contributions from outdoors, indoor emissions, and secondary OA formation. Inorganic aerosol is predicted from outdoor-to-indoor transport. Building parameters were set by distributions representing U.S. residences. A seasonal and regional dataset spanning 16 U.S. climate zones informed outdoor climatic (temperature, RH) and pollution parameters (organic and inorganic aerosol concentrations, composition). The 2D-VBS constrains OA O:C, informing OA hygroscopicity. Using organic and inorganic aerosol composition, aerosol liquid water (ALW) was predicted using κ-Kohler theory. Indoor RH drives ALW, and regional and seasonal conditions impacted indoor RH and thus ALW. Ratios of indoor ALW to dry particle mass reached ~0.4 in hot/humid climates during summer, while values largely remained <0.1 year-round for arid climates and during winter in most regions. The ALW associated with OA was used to compute OA phase state (liquid, semisolid, amorphous solid). Residential OA most likely exists as a semisolid. However, certain hot/humid conditions yield liquid indoor OA, while indoor OA may be amorphous solid in cold or arid climates. These trends imply that partitioning of much indoor OA may have kinetic limitations inhibiting gas-to-particle equilibrium assumptions compared to residence timescales of indoor air, and that heterogeneous reactions may be slowed. However, using equilibrium partitioning assumptions, we predicted that ambient OA will generally condense as it goes indoors and encounters a greater absorbing mass of indoor-sourced OA. This effect will be exaggerated if indoor temperatures are colder than outside, but may be mitigated or reversed if the opposite is true.