Dynamic behavior of airborne ultrafine particles in buildings

Donghyun Rim, Ph.D.
James L. Henderson Jr. Memorial Assistant Professor
Department of Architectural Engineering
Pennsylvania State University

Indoor ultrafine particles (UFP, < 100 nm) emitted from combustion and consumer products lead to elevated human exposure to UFP. Once emitted from a source, indoor particles undergo aerosol transformation processes such as coagulation and deposition. Coagulation effect can be significant during the source emission due to high number concentration and high  mobility  of  UFP.  However,  few  studies  have  estimated  size-resolved  UFP  source emission strengths by considering coagulation. The objective of this study is to characterize size-resolved UFP emission strength by considering coagulation in addition to deposition and ventilation in a realistic setting.

Experimental investigations were performed in a full-scale test building to examine UFP emissions from three common indoor UFP sources: electric stove, natural gas burner, and paraffin wax candle. Size- and time- resolved concentrations of UFP ranging from 2 nm to 100 nm were monitored using a Scanning Mobility Particle Sizer (SMPS). Based on the temporal evolution of particle size distribution during the source emission period, unimodal and log-normal source  emission  rates  were  determined  using  a  material-balance  modeling approach.

The results indicated that for a given UFP source, the source strength varied with particle size and source type. The geometric mean of the size-resolved source emission ranged from 5 to 8 nm for both electric and gas stoves while it ranged between 3 and 4 nm for the candle. These  results  reflect  that  majority  of  the  primary  particles  originated  from  indoor combustion or high temperature process are smaller than 10 nm.  The discrepancy in estimates of source strength due to coagulation effect was observed up to a factor of 8, implying that previous studies on indoor UFP source strengths considering only deposition and ventilation might have largely underestimated the true values of UFP source strengths.

Dr. Donghyun Rim is a James L. Henderson Jr. Memorial Assistant Professor in Architectural Engineering at Pennsylvania State University. His research focuses on indoor aerosol dynamics, transport of reactive organic gases around human body, and air quality in energy efficient buildings. Before joining Penn State in 2014, Dr. Rim worked as a postdoctoral researcher at UC Berkeley and LBNL, and studied indoor environmental quality in tropical climates. Dr. Rim earned his Ph.D./M.S. degrees in Environmental Engineering from the University of Texas at Austin.  He earned his B.S. degree in Civil and Environmental Engineering from Hanyang University in Seoul, Korea.