AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Influence of Gas-Phase and Heterogeneous OH Aging Reactions on Indoor Organic Aerosol Loading and SOA Formation
BRYAN CUMMINGS, Michael Waring, Drexel University
Abstract Number: 454 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Organic aerosols (OA) continually undergo chemical aging transformations via oxidation reactions, for instance with hydroxyl radicals (OH). Broadly, these transformations include molecular functionalization and fragmentation. OA is a system with particle-bound organic material (OM) and gaseous OM in a state of thermodynamic gas-to-particle equilibrium. OM in either phase may undergo transformations, causing their volatility and degree of oxygenation to change, potentially increasing or decreasing the condensed OA concentration (COA). The two-dimensional volatility basis set (2D-VBS) constrains OM volatility and degree of oxygenation, models how each change throughout OH aging processes, and also predicts thermodynamic partitioning and resulting COA. Potential OA aging impacts were assessed by using the 2D-VBS framework within a larger indoor chemistry model which also predicts the indoor ozone and OH concentrations, oxidation of volatile organics, secondary OA (SOA) formation, and OA by indoor emissions and outdoor-to-indoor transport. Using input distributions characteristic of U.S. residences, indoor OH was predicted as not typically high enough to meaningfully impact COA by aging processes on a daylong time-averaged basis (increases of <5%). However, reasonable and individual circumstances were modeled where OA transformations due to OH-induced aging accounted for increases in COA of ~30%. One such case was a room where ample sunlight led to a high temperature and generation of OH by photolytic reactions with nitrous acid (HONO) sourced from indoor surfaces. High temperatures encourage more OM to exist in the gas phase where it more quickly reacts with OH (compared to heterogeneous reactions) and subsequently may condense into the particle phase. Additionally, simulated terpene-based cleaning events led to similar increases in OA due to OH-induced aging. These results will be discussed.