Particle Deposition and Decay in a Chamber and the Implications to Exposure Assessment

Abstract

Accurate modeling indoor aerosol deposition and decay is an important step for exposure assessment. High deposition rate reduces indoor pollutant concentration and results in lower inhalation exposure. Many of indoor surfaces have random roughness protrusion scales up to several millimeters which it may significantly affect the deposition loss rate. Aerosols deposition onto most indoor surfaces can be considered as "rough" surface deposition. However, particle deposition from an indoor environment is frequently modeled by assuming that surfaces are smooth. In this work, experimental results for deposition velocity onto drywall surfaces for supermicron particles from 1 to 7 μm are presented. Deposition velocity is significantly higher than that predicted by a previous published model. To illustrative the influence of particle deposition on exposure, two hypothetical room sizes and two air exchange rates were considered. Inhalation transfer factor was adopted as a risk exposure index. Taking into account of high deposition velocity onto drywall surfaces, inhalation transfer factors are 8 to 35% lower than that predicted by the model and this significant difference is important to the exposure assessment.

Size Dependence of the Ratio of Aerosol Coagulation to Deposition Rates for Indoor Aerosols

“…The particle deposition rate coefficient is, therefore, an essential parameter to estimate the fate of particles in an enclosed space or indoor environment, and it is also a key quantity when particle size-resolved emission rates or sink rates are characterized Hussein et al 2009Hussein et al , 2012Koivisto et al 2010;Koivisto et al 2012). Nowadays, using size-resolved measurements such as scanning mobility particle sizers (SMPS), optical particle counters (OPC), and aerodynamic particle sizers (APS), the deposition rate coefficient is generally estimated from measured data for aerosols with low number concentration where coagulation can supposedly be ignored when compared to deposition (Lai 2002;Lai et al 2002;Riley et al 2002;Thatcher et al 2002;He et al 2005;Lai and Nazaroff 2005;Lai 2006;Hussein et al 2009). However, up to now, there is a lack of fundamental understanding regarding the ratio of the rates of coagulation and deposition for aerosols with wide size distributions.…”

“…Many researchers have used this equation and a subsequent analytical approximation to describe particle deposition quantified by mass or number in experimental chambers or indoor environments (Lai 2002;Lai et al 2002;Thatcher et al 2002;He et al 2005;Lai and Nazaroff 2005;Lai 2006;Hussein et al 2009). However, there is not yet a universal criterion to evaluate whether coagulation can in fact be ignored relative to deposition for a specific aerosol.…”

Ultrafine Particles Deposition Inside Passenger Vehicles

“…Most previous indoor studies on particle deposition were conducted in experimental chambers (Byrne et al 1995;Thatcher et al 1995;Morawska and Jamriska 1996;Cheng 1997;Nomura et al 1997;Abadie et al 2001;Mosley et al 2001;Lai et al 2002;Lai and Nazaroff 2005;Lai 2006; Afshari and Reinhold 2008), and in residential or experimentally controlled houses (Fogh et al 1997;Abt et al 2000;Long et al 2001;Vette et al 2001;Riley et al 2002;Thatcher et al 2002;Howard-Reed et al 2003;Wallace et al 2004a;He et al 2005). Besides particle deposition, these studies also laid emphasis upon the effects of other influencing factors on indoor particle concentrations, such as the indoor-outdoor particle concentration ratio, the penetration rate of outdoor particles, and indoor particle concentrations due to daily human activities.…”

Deposition of Fine and Ultrafine Particles on Indoor Surface Materials

“…In recent years, exposure to fine and ultrafine airborne particles has been identified as an important risk factor for human health [1]. Deposition of particles on indoor surfaces such as floors, walls, ceilings, and furniture may be thought of as a phenomenon protecting humans from some of the dangers caused by exposure to particles [2,3].…”