) who were at least 16 years old. The survey instruments used in this study ( and also in Toronto ) included a household screener form ( HSF ), a study questionnaire ( SQ ), and a time and activity questionnaire ( TAQ ). The SQ was administered to elicit information about the participant and his / her activities, occupation, and surroundings that might be relevant to his / her exposure to particles and Mn. In addition to the personal particulate matter ( PM ) and elemental 3 -day monitoring, 240 participants completed a TAQ on a daily basis during the actual monitoring period. Also, a subset of participants had 3 -day outdoor and indoor stationary monitoring at their home ( approximately 58 observations ), and sampling was conducted at a fixed site ( approximately thirty -three 3 -day observations ). The quality of data was assessed and compared to the Toronto study in terms of linearity of measurement, instrument and method sensitivity, measurement biases, and measurement reproducibility. Twenty -six of the sample filters were subjected to two analyses to characterize the within -laboratory component of precision in terms of relative standard deviations ( RSDs ). The median RSD for Mn was 8.7%, as compared to 2.2% for Toronto. The quality assurance ( QA ) laboratory exhibited a clear positive bias relative to the primary laboratory for Al and Ca, but no systematic difference was evident for Mn. A high interlaboratory correlation ( > 0.99 ) was also attained for Mn. Mean field blank results for PM and Mn were 0.87 g / m 3 and 0.71 ng / m 3 , respectively, which were comparable to the Toronto study. The median RSDs for colocated fixed site and residential samples ranged from 2.2% to 9.0% for PM and from 8.8% to 15.3% for Mn, which were close to those observed in Toronto. For the PM 10 , the 90th percentile indoors was 124 g / m 3 compared with 54 g / m 3 outdoors. This pattern was even more pronounced for the PM 2.5 data ( 90th percentiles of 92 g / m 3 indoors vs 30 g / m 3 outdoors ). Personal PM 2.5 was somewhat higher than the indoor levels, but the percentiles seemed to follow the more highly skewed pattern of the indoor distribution. This difference was largely due to the presence of some smokers in the sample; e.g., exclusion of smokers led to a personal exposure distribution that was more similar to the outdoor distribution. The estimated 90th percentile for the nonsmokers' personal exposures to PM was 43 g / m 3 compared with 84 g / m 3 for the overall population. In general, the Indianapolis PM levels of a given type and cut size were somewhat higher than the levels observed in Toronto, e.g., the median and 90th percentile for the personal PM 2.5 exposures were 23 and 85 g / m 3 , respectively, in Indianapolis, while in Toronto, the corresponding percentiles were 19 and 63 g / m
3. The cities' distributions of the proportion of the PM 10 mass in the 2.5 -m fraction appeared similar for the residential outdoor data ( medians of 0.67 and 0.65 for Indianapolis and Toronto, respectively, and 90th percentile...
