Air pollution monitoring design for epidemiological application in a metropolitan area

Abstract

Introduction: The association between long-term exposures to air pollution and health in cohort studies was assessed by relying on spatial contrasts in exposures and outcomes. However, existing regulatory monitoring networks may not represent sufficient spatial contrasts of air pollution exposures across people’s residences. We aimed to develop an air pollution monitoring design to supplement regulatory monitoring networks in Seoul, Korea. This design specifically focused on the selection of 20 new monitoring sites for representing spatial variability of PM2.5 and NO2 across Seoul residents for the application to epidemiological studies. Methods: We computed annual averages of PM2.5 and NO2 at 37 regulatory monitoring sites during 2010 in Seoul, Korea. About 300 geographic variables representing various pollution sources were computed at regulatory monitoring sites, 38,201 participants’ homes of the Atopy Free School survey, and 422 community service centers in Seoul. The design included three procedures. We selected five geographic variables most related to each of PM2.5 and NO2 from regulatory monitoring data. Then, k-means clustering was used for categorizing all locations into groups representing contrasts in five selected variables. Finally, using community service centers as candidate sites, we randomly selected ten new sites from clusters with low ratios of regulatory monitoring sites to participant homes. Results: Five selected variables generally included variables relevant to traffic and urbanicity with cross-validated R2s of 0.69 and 0.58 for PM2.5 and NO2, respectively. K-means clustering gave eight and night clusters for PM2.5 and NO2, respectively, representing different geographic characteristics. One to three new monitoring sites were selected from four to six clusters for PM2.5 and NO2. Conclusions: Our monitoring design provides a useful tool applicable to metropolitan areas for assessing air pollution levels of people and resulting health effects.