lndoorpm2.5samples were collected using a Harvard personal Exposure Monitor(pem)with a MEDO linear-piston vacuum pump.teflon filters(37mm)were pre and post-weighed in a temperature and relative humidity(RH)-contolled(20.0c and 35%RH)glove box(plaslabs model890thc lansing ml)on an ultramicrobalance (mettle toledo model xp2U colnbus OH)pm2.5concentraiins were calculated using the two PEMs from each home and averaged.for overallpm2.5