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Estimating particle exposure in the Mexico City metropolitan area
Marie S O'Neill1, Dana Loomis, Victor Torres Meza
1University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. moneill@hsph.harvard.edu
Study Question:
We examined whether methods for measuring exposure to airborne particles less than 10 microm in aerodynamic diameter (PM10) in the Mexico City metropolitan area give different estimates of PM10 levels, and the nature of these differences, and developed a model for estimating missing PM10 data for one measurement method.
Methods:
Government PM10 measurements using two different technologies at five sites (the Sierra-Anderson PM10 High-Volume Air Sampler System, Hi-Vol) (every sixth day) and the Rupprecht and Patashnik Tapered Element Oscillating Microbalance (TEOM) monitor (daily), as well as Harvard Impactor (HI) data collected for research purposes from one monitoring station were matched by day and monitoring site, then compared visually and with basic descriptive statistics. We fit linear regression models with airport visual range measurements, meteorological data, and information on other air pollutants to predict the Hi-Vol measured PM10 levels for those days when direct measurements were not available.
Results:
We found relatively low correlations (r ranging from 0.46 to 0.63) between PM10 measured with the TEOM and Hi-Vol methods, and highly variable differences (0-70 microg/m(3)) between the means of these measurements, depending on monitoring site. The HI measurements had a relatively high correlation with the Hi-Vol measurements (r=0.90). The models developed for the missing Hi-Vol measurements provided a series of estimated values similar to the actual Hi-Vol measurements, although the estimated series did not have high values in the range observed in the measured data.
Conclusions:
The differences we observed in the PM10 measurements across methods in Mexico City may be important when studying health effects associated with particle exposure, evaluating method performance under conditions and operating protocols similar to those in Mexico City, and determining compliance with air quality standards. The estimated series of PM10 measures may be a useful index of exposure for use in studies of the effects of air pollution on health.