The Effect of PM2.5 Composition on the Fraction of Outdoor-Generated PM2.5 in Indoor Air

NATASHA HODAS (1), Melissa Lunden (2), Qing Yu Meng (3), David Rich (4), Haluk Ozkaynak (5), Barbara Turpin (1)

(1) Rutgers University, New Brunswick, NJ, (2) Lawrence Berkeley National Laboratory, Berkeley, CA, (3) US EPA National Center for Environmental Assessment, Research Triangle Park, NC, (4) US EPA National Exposure Research Laboratory, Research Triangle Park, NC, (5) University of Medicine and Dentistry of New Jersey, School of Public Health, Piscataway, NJ

     Abstract Number: 508
     Last modified: May 13, 2010

Abstract
Central site PM$_(2.5) is commonly used as a surrogate for personal or population exposure to ambient PM$_(2.5) in epidemiology; however, people spend the majority of time indoors, where they are exposed to outdoor and indoor generated pollutants. The concentration and composition of ambient PM$_(2.5) are altered with outdoor-to-indoor transport. If the fraction and composition of ambient PM$_(2.5) found indoors varies temporally or across communities (spatially), the exposure error introduced by ignoring the indoor environment could alter the epidemiological findings. Indoor concentrations of outdoor-generated PM$_(2.5) depend on the outdoor concentration, building air exchange rate (AER), the efficiency of penetration of outdoor-generated particles, indoor losses by deposition, and phase changes of semi-volatile compounds. AER varies within homes (temporally), due to meteorology and human activities, and spatially because of differences in housing characteristics, and human activities. Particle penetration efficiency and deposition loss rates in the indoor environment are highly dependent on particle diameter. While PM$_(2.5) mass size distributions are highly variable, size distributions of individual species are less variable because they are dictated by formation mechanisms. This work examines the importance of size distribution data to estimates of ambient PM$_(2.5) in indoor spaces. Measured PM$_(2.5), AER, and available information about PM$_(2.5) species size distributions are used to examine the effects of PM$_(2.5) composition on the fraction of ambient PM2.5 found indoors (F) using an aerosol penetration and persistence mass balance model. Effects of AER and composition will be discussed in the context of their contribution to exposure error in PM$_(2.5) epidemiology.