Predicting Floor-Based Variability in Composition and Concentration of Indoor Aerosol of Outdoor Origin in a High-Rise Multi-Family Building

XINXIU TIAN, Bryan Cummings, Michael Waring, Marianne Touchie, Peter F. DeCarlo, Johns Hopkins University

     Abstract Number: 386
     Working Group: Indoor Aerosols

Abstract
In this work, we model how the differences in building ventilation rates by floor and variation in outdoor aerosol concentration and composition impact indoor aerosol within a high-rise multi-family building. In the absence of strong indoor sources, outdoor-originated aerosols are the main contributor to indoor aerosols. Upon transport to the indoor environment, both concentrations and chemical compositions of outdoor aerosols are modified. Many studies show the linkage of indoor concentrations of ambient PM_2.5 to various factors, including infiltration, ventilation rates, deposition and filtration, and phase change of semi-volatile material during outdoor-to-indoor transport. We demonstrate that inconsistent airflow patterns caused by natural and mechanical ventilation within a single building can induce differences in indoor concentrations of outdoor PM_2.5. Airflow and pollutant simulations were performed with a CONTAM building model to obtain the indoor-outdoor ratio of a non-volatile, non-reactive test species under different ambient temperatures. Chemical compositions of ambient PM_2.5 were reconstructed from regulatory monitoring data based on modified PM_2.5 mass reconstruction techniques. Outdoor PM concentration and composition were used to calculate indoor-outdoor ratios of semi-volatile species including NO₃, HOA, and OOA using linear relationships developed by previous modeling work. Indoor-outdoor ratios and, by extension, concentrations and composition of particulate chemical species showed variation across seasons and by floor due to non-uniform building ventilation air distribution. This work demonstrates that there are significant temperature-based and floor-based variations in indoor-outdoor ratios of chemical species within a single building, with variations in chemical compositions of ambient PM_2.5, resulting in strong seasonal and floor-based variations in indoor concentrations and compositions of ambient species.