Samplers were placed in the main activity room,away from windiws and combustion or heat sourcs.After three days,the PEM was replaced to avoid particle overload on the impactor plate and perturbation of the particle size cut-point. To adsess reproducibility two hones were randomly selected each sason for co-located sampling A stadardardized log sheet was used to record sampking start and stop times,and questinnaire on indoor source activities was administered in-person to an adult resident of each horne on the final sampling day.