Exposure of Chronic Obstructive Pulmonary Disease Patients to Particulate Matter: Relationships between Personal and Ambient Air Concentrations

Abstract

Most time-series studies of particulate air pollution and acute health outcomes assess exposure of the study population using fixed-site outdoor measurements. To address the issue of exposure misclassification, we evaluate the relationship between ambient particle concentrations and personal exposures of a population expected to be at risk of particle health effects. IMPLICATIONSAs epidemiological studies aim to attribute observed health effects to outdoor air pollution, the contribution of outdoor air pollutants to population exposure must be assessed. To support time-series epidemiological studies that evaluate the health impacts of short-term changes in air pollution, an exposure metric is required for which the day-to-day variability in personal exposures reflects the variability of ambient concentrations being measured. We found that personal exposures to particulate sulfate in a group of subjects at risk for adverse health effects of particulate air pollution were highly correlated, over time, with ambient particle concentrations. Personal exposures to sulfate were highly correlated with ambient levels across all individuals and all levels of exposure, whereas correlations between personal exposures to PM 2.5 and ambient particle concentrations were lower and more variable. Overall, we have shown that a personal measure of exposure to outdoor source PM is highly related to variation in ambient levels of PM, lending support to time-series epidemiological studies.Sampling was conducted within the Vancouver metropolitan area during April-September 1998. Sixteen subjects (non-smoking, ages 54-86) with physician-diagnosed chronic obstructive pulmonary disease (COPD) wore personal PM 2.5 monitors for seven 24-hr periods, randomly spaced approximately 1.5 weeks apart. Time-activity logs and dwelling characteristics data were also obtained for each subject. Daily 24-hr ambient PM 10 and PM 2.5 concentrations were measured at five fixed sites spaced throughout the study region. SO 4 2-, which is found almost exclusively in the fine particle fraction and which does not have major indoor sources, was measured in all PM 2.5 samples as an indicator of accumulation mode particulate matter of ambient origin.The mean personal and ambient PM 2.5 concentrations were 18 µg/m 3 and 11 µg/m 3 , respectively. In analyses relating personal and ambient measurements, ambient concentrations were expressed either as an average of the values obtained from five ambient monitoring sites for each day of personal sampling, or as the concentration obtained at the ambient site closest to each subject's home. metric, the median r between personal and average ambient concentrations was 0.96 (range = 0.66 to 1.0). Use of the closest ambient site did not improve the median correlation of the group for either PM 2.5 or SO 4 2-. All pooled analyses resulted in lower correlation coefficients than the median correlation coefficient of individual regressions. Personal SO 4 2-was more highly correlated with all ambient measures than PM 2.5 ....

Effects of thoracic and fine PM and their components on heart rate and pulmonary function in COPD patients

“…Personal-central site correlations are higher when data were observed longitudinally than crosssectionally (Ebelt et al, 2000;Liu et al, 2003). We also reported higher longitudinal personal-indoor-outdoor correlations when compared with cross-sectional correlations across our two cities and seasons in our companion paper (Hsu et al in review in JESEE).…”

Estimating effects of ambient PM2.5 exposure on health using PM2.5 component measurements and regression calibration

“…Recently, personal exposure monitors (henceforth called personal monitors) have been used in some air pollution studies to get a better idea of how ambient pollution concentrations relate to personal breathing zone exposures (Janssen et al, 1997(Janssen et al, , 1998(Janssen et al, , 1999Ebelt et al, 2000;Rojas-Bracho et al, 2000;Williams et al, 2000;Liu et al, 2003). Some have argued that moderate to strong correlations between (average) personal 1.…”

Exposure time and place: Do COPD patients differ from the general population?

“…The data from these panel studies shows that time indoors at home ranged from 70% (Rojas-Bracho et al, 2000) to 92% (Ebelt et al, 2000). In Boston (Rojas-Bracho et al, 2000, 2004 more time was spent indoors in winter (91%) than in summer (84%) and more time was spent outdoors in summer (7%), than in winter (o1%).…”

“…Timeactivity data in these studies usually examined 12 h daytime time-activity diaries, often self-administered, and in conjunction with particulate exposures of which the subjects were aware. One study which did not use 24 h data logs compared their results to NHAPS data (Ebelt et al, 2000) but the timeactivity data collection was in a diary methodology, subjects were aware of the indoor air exposures, were carrying a personal sampler of some significant weight and only current nonsmokers were sampled. Time-activity data results have been shown to be sensitive to the method of collection (Johnson et al, 1993) and may also be sensitive to these other factors.…”

“…In personal particulate exposure studies, small panels of COPD patients wearing monitors have also kept timeactivity data logs (Ebelt et al, 2000;Rojas-Bracho et al, 2000, 2004Sarnat et al, 2000;Allen et al, 2003;Liu et al, 2003) but subjects were aware of particulate exposure questions, wore the added weight of the samplers and only nonsmokers could be studied.…”