Research Program Area: Health & Exposure
A study entitled “Detailed Characterization of Indoor and Personal Particulate Matter Concentrations” was conducted to characterize indoor and personal exposures to PM2.5, its major components, and to specific-size ranges for households located in the Los Angeles, CA (LA) metropolitan area. This study is a continuation of our efforts to characterize exposures to particles and their constituents. It complements our CARB-US EPA-funded study characterizing the PM exposures of individuals with chronic obstructive pulmonary disease (COPD) living in LA (Chang and Suh, 2003) and was conducted with co-funding from the US EPA to allow a more comprehensive indoor characterization study to be performed. In this study, PM2.5, black carbon (BC), nitrate (NO3 - ), and size-resolved particle volume concentrations were measured continuously inside and outside 17 LA homes. In addition, 24-h personal PM10, PM2.5, BC, NO3 - exposures were measured for one individual living in each household. Daily time-activity and housing characteristics data were also collected for each household, while a house dust sample was collected in each home on one of the monitoring days. Data from our study provided novel and important information about the composition and size distribution of PM in LA homes, as it – for the first time – combined measurements of PM size and composition with data on air exchange rates, ventilation conditions, and activity patterns. Mean 20-minute outdoor PM2.5 (32.1+33.1 ug/m 3 ), BC (2.3+2.0 ug/m 3 ) and NO3 - (12.0+10.6 ug/m 3 ) concentrations were higher than their corresponding indoor levels (17.9+18.7, 1.9+1.7, 3.5+6.1 ug/m 3 , respectively). Diurnal variation in 20-minute indoor concentrations was found for all particulate species, which was generally related to diurnal variability outdoors. Nighttime FINF values estimated using indoor/outdoor ratios and regression techniques showed patterns consistent with particle theory. FINF values were highest for BC, which was expected given its non-reactive nature and its size (~0.1-0.5 um). Correspondingly, FINF values were lowest for fine particle NO3 - , a highly reactive pollutant that in LA may consist primarily of particles larger than 1.0 um. Nighttime FINF for PM2.5 fell between those for BC and NO3 - . Correspondingly, the estimated value of P obtained using mass balance models was also highest for BC and lowest for NO3 - (0.18±0.13), with the estimate for PM2.5 again roughly equidistant between those for BC and NO3 - (0.42±0.11). Estimated values for P were consistent with winter and were lower than summer estimates from our Boston study, with the low value likely resulting from the large contribution of NO3 - to PM2.5 in LA. Estimated values of P and k using dynamic models were generally imprecise, providing further evidence that the separate effects of P and k could not be estimated under “real-world” conditions. 24-h PM2.5, NO3 - and BC were highest outdoors (mean=28.8, 10.8, and 1.7 ug/m 3 , respectively), with personal (17.7, 3.8, 1.8 ug/m 3 , respectively) and indoor (17.6, 3.0, 1.6 ug/m 3 , respectively) levels comparable. Personal PM2.5, NO3 - and BC exposures were significantly associated with indoor and outdoor levels. Slopes of the indoor-outdoor longitudinal regressions were comparable to those found using 20-minute data, suggesting that estimates of the effective penetration efficiencies for PM2.5, NO3 - and BC are stable. The slopes and intercepts for personal-outdoor regressions for all particulate species were similar to those for the indoor-outdoor associations, suggesting that personal exposures to ambient particles occur primarily indoors and that indoor concentrations are on average equivalent measures of personal particulate exposures.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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