Modeling Transformations in Indoor Inorganic Aerosol Composition and Concentrations When Passing through an HVAC System with ISORROPIA

BRYAN BERMAN, Bryan Cummings, Xinxiu Tian, Peter F. DeCarlo, Shannon Capps, Michael Waring, Drexel University

     Abstract Number: 296
     Working Group: Indoor Aerosols

Abstract
Aerosol constituents are transformed as they are transported through ventilation systems into buildings. For instance, changes in temperature and relative humidity (RH) between indoors and outdoors influence the partitioning of specific aerosol components. Previously, IMAGES (Indoor Model of Aerosols, Gases, Emissions, and Surfaces), a modeling platform that simulates indoor organic aerosol, was extended to incorporate the inorganic aerosol (IA) thermodynamic equilibrium model, called ISORROPIA. ISORROPIA estimates partitioning of inorganic aerosols and precursor gases. The model was previously applied to simulate indoor IA in a classroom during the summer and winter with measurements from Avery et al. (2019). However, the model was limited because impacts from the heating, ventilating, and air conditioning (HVAC) system were not included. Modeling inorganic aerosols through the HVAC system will allow a deeper understanding of the influence of large temperature and RH gradients across heating and cooling coils, which influence aerosol partitioning. Additionally, gases such as ammonia and nitric acid can be lost with condensate water, and particles may be lost to the filter, cooling coil, and heating coil. An HVAC module was developed to address this gap. The model was evaluated against measurements of PM₁, PM_2.5, and PM₁₀, temperature and RH from multiple locations in the HVAC system of a building at Johns Hopkins University during select periods of winter and summer of 2021. This module will be incorporated into the IMAGES framework to better simulate indoor IA of outdoor origin.