Abstract View
Modeling Indoor Aerosol Inorganic Thermodynamics with ISORROPIA
BRYAN BERMAN, Bryan Cummings, Anita Avery, Shannon Capps, Peter F. DeCarlo, Michael Waring, Drexel University
Abstract Number: 551
Working Group: Indoor Aerosols
Abstract
Many indoor aerosols originate from the outdoor environment. However, certain aerosol components may be physically or chemically processed upon transport from outdoors to indoors. For instance, temperature and relative humidity (RH) gradients between the indoors and outdoors may influence the repartitioning of certain aerosol components. Cummings and Waring (2019) developed a model that simulates indoor organic aerosol (OA) concentration, composition, partitioning behavior, and secondary formation. We expand this model to predict inorganic aerosol (IA) repartitioning by integrating the thermodynamic model, ISORROPIA, which predicts concentrations of various inorganic species in the aerosol and gas phases at chemical equilibrium. To our knowledge, this is the first instance of applying ISORROPIA in an indoor model to simulate indoor IA thermodynamics. Specifically, we modeled inorganic concentrations and compared them to indoor aerosol concentration measurements from aerosol mass spectrometer (AMS) data obtained by Avery et al. (2019). To evaluate the model, sulfate normalized indoor-to-outdoor concentration ratios, which may be used to distinguish repartitioning losses from physical loss mechanisms, were computed for inorganic NO3 ([I/O]NO3/SO4) across the simulation set. Our simulated [I/O]NO3/SO4 were then compared to observed data from Avery et al. (2019). Both exhibited qualitatively similar exponentially decaying curves with respect to the indoor-outdoor temperature difference, ΔT. The simulated [I/O]NO3/SO4 were heavily influenced by ammonia concentrations. However, the exponential trends of both were in agreement when sufficient indoor ammonia sources were modelled, from both human occupants and surface reservoirs. This model evaluation serves as a proof of concept towards modeling chemical processes of inorganic aerosols and gases at key points in a heating, ventilating, and air-conditioning (HVAC) system, in the summer and winter, with ISORROPIA. Therefore, future work will involve exploring how HVAC systems influence indoor aerosol composition and chemical processing, with a focus on indoor aerosols of outdoor origin.