Indoor dynamics of chemically reactive/secondary aerosols: New data, case studies, and implications for human exposure
P.J. Lioy, Q. Sun, T. Fan, P.G. Georgopoulos (EOHSI, UMDNJ - R.W. Johnson Medical School and Rutgers University)
Evaluation of human exposure to complex atmospheric contaminants such as primary and secondary particulate matter (PM) is often based on measured data from fixed ambient monitoring stations. This results in an artificial characterization of human exposures and doses, as the concentrations and physicochemical attributes of aerosols actually inhaled vary significantly and are in general quite different from corresponding outdoor monitor values. An example of a process that can be potentially important for exposure/dosimetry considerations is the indoor formation of ultra-fine secondary organic aerosol, through chemical reactions involving ozone entrained from outdoors and emissions of volatile organics from household products use. Indoor air chemistry studies conducted in our Controlled Environmental Facility (CEF) at EOHSI have shown that under typical indoor conditions a significant amount of fine particles is formed when air with ozone concentration of only 40 ppb is introduced into the CEF, in the presence of volatile organic compounds commonly found in the indoor environment. We also observed that the size of particles increased with time in the chamber over a 4-hour experiment. This suggests that the smaller particles, initially generated by gas-phase reactions between ozone and unsaturated VOCs, participate in dynamic processes, such as coagulation, to form larger particles as a function of time. These fine particles may contribute to the acute respiratory effects and could have relatively more health impacts than indoor VOCs.
The present study utilizes MENTOR, the Modeling Environment for Total Risk studies, to study indoor gas/particle interactions. MENTOR is an evolving framework that provides a set of novel mechanistically-based modeling tools aiming to improve the assessment of human (both individual and population) exposures and doses to - possibly co-occurring photochemical pollutants and fine airborne particles. Here, the Indoor Air Quality (IAQ) modules of MENTOR are used to model physical and chemical processes involving secondary aerosols formation through indoor air chemistry, and to predict the fine particles mass concentrations, chemical compositions, and size distributions. Currently MENTOR-IAQ provides two alternative methods for modeling indoor aerosol dynamics: one is based on the equilibrium aerosol module (AERO) developed by Sonoma Technology Inc.; the second is based on the sectional dynamic aerosol module (UDAERO) developed at University of Delaware. The adequacy of existing aerosol dynamics modules is evaluated through the comparison of the modeling results with the experimental data from the CEF studies. Extensions/modifications to these modules to address deficiencies in existing formulations are also presented.