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Joint Effects of Ambient Air Pollutants on Pediatric Asthma Emergency Department Visits in Atlanta, 1998–2004

Winquist, Andreaa; Kirrane, Ellenb; Klein, Mitcha; Strickland, Matthewa; Darrow, Lyndsey A.c; Sarnat, Stefanie Ebelta; Gass, Katherinec; Mulholland, Jamesd; Russell, Armisteadd; Tolbert, Paigea

doi: 10.1097/EDE.0000000000000146
Air Pollution

Background: Because ambient air pollution exposure occurs as mixtures, consideration of joint effects of multiple pollutants may advance our understanding of the health effects of air pollution.

Methods: We assessed the joint effect of air pollutants on pediatric asthma emergency department visits in Atlanta during 1998–2004. We selected combinations of pollutants that were representative of oxidant gases and secondary, traffic, power plant, and criteria pollutants, constructed using combinations of criteria pollutants and fine particulate matter (PM2.5) components. Joint effects were assessed using multipollutant Poisson generalized linear models controlling for time trends, meteorology, and daily nonasthma upper respiratory emergency department visit counts. Rate ratios (RRs) were calculated for the combined effect of an interquartile range increment in each pollutant’s concentration.

Results: Increases in all of the selected pollutant combinations were associated with increases in warm-season pediatric asthma emergency department visits (eg, joint-effect RR = 1.13 [95% confidence interval = 1.06–1.21] for criteria pollutants, including ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and PM2.5). Cold-season joint effects from models without nonlinear effects were generally weaker than warm-season effects. Joint-effect estimates from multipollutant models were often smaller than estimates based on single-pollutant models, due to control for confounding. Compared with models without interactions, joint-effect estimates from models including first-order pollutant interactions were largely similar. There was evidence of nonlinear cold-season effects.

Conclusions: Our analyses illustrate how consideration of joint effects can add to our understanding of health effects of multipollutant exposures and also illustrate some of the complexities involved in calculating and interpreting joint effects of multiple pollutants.

Supplemental Digital Content is available in the text.

aDepartment of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA; bNational Center for Environmental Assessment, Environmental Protection Agency, Durham, NC; cDepartment of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA; and dSchool of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA.

Submitted 24 September 2013; accepted 10 April 2014; posted 18 July 2014.

This publication was made possible by US Environmental Protection Agency (USEPA), contract EP-12-H-000093, National Institutes of Health (NIH) grant K01ES019877, and USEPA grant R834799. The views expressed in this manuscript are those of the authors and do not necessarily represent the views or policies of the USEPA. Further, USEPA does not endorse the purchase of any commercial products or services mentioned in the publication. Support for the original emergency department study was provided by grants from NIH (R01ES011294), USEPA (STAR R829213-01), and the Electric Power Research Institute (EP-P27723/C13172).

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article ( This content is not peer-reviewed or copy-edited; it is the sole responsibility of the authors.

Correspondence: Andrea Winquist, 1518 Clifton Road NE, Atlanta, GA 30322. E-mail:

© 2014 by Lippincott Williams & Wilkins, Inc