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Nadia N. Hansel,¹ Patrick N. Breysse,² Meredith C. McCormack,¹ Elizabeth C. Matsui,³ Jean Curtin-Brosnan,³ D'Ann L. Williams,² Jennifer L. Moore,¹ Jennifer L. Cuhran,¹ and Gregory B. Diette¹

¹Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA; ²Department of Environmental Health Sciences, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA; ³Department of Pediatrics, School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA

Abstract
Background: The effect of indoor nitrogen dioxide concentrations on asthma morbidity among inner-city preschool children is uncertain.

Objectives: Our goal was to estimate the effect of indoor NO₂ concentrations on asthma morbidity in an inner-city population while adjusting for other indoor pollutants.

Methods: We recruited 150 children (2–6 years of age) with physician-diagnosed asthma from inner-city Baltimore, Maryland. Indoor air was monitored over a 72-hr period in the children's bedrooms at baseline and 3 and 6 months. At each visit, the child's caregiver completed a questionnaire assessing asthma symptoms over the previous 2 weeks and recent health care utilization.

Results: Children were 58% male, 91% African American, and 42% from households with annual income < $25,000 ; 63% had persistent asthma symptoms. The mean (± SD) in-home NO₂ concentration was 30.0 ± 33.7 (range, 2.9–394.0) ppb. The presence of a gas stove and the use of a space heater or oven/stove for heat were independently associated with higher NO₂ concentrations. Each 20-ppb increase in NO₂ exposure was associated significantly with an increase in the number of days with limited speech [incidence rate ratio (IRR) = 1.15 ; 95% confidence interval (CI) , 1.05–1.25], cough (IRR = 1.10 ; 95% CI, 1.02–1.18) , and nocturnal symptoms (IRR = 1.09 ; 95% CI, 1.02–1.16) , after adjustment for potential confounders. NO₂ concentrations were not associated with increased health care utilization.

Conclusions: Higher indoor NO₂ concentrations were associated with increased asthma symptoms in preschool inner-city children. Interventions aimed at lowering NO₂ concentrations in inner-city homes may reduce asthma morbidity in this vulnerable population.

Key words: asthma, indoor pollutants, inner city, nitrogen dioxide, preschool. Environ Health Perspect 116:1428–1432 (2008) .  doi:10.1289/ehp.11349 available via http://dx.doi.org/ [Online 23 July 2008]

Address correspondence to G.B. Diette, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, 1830 East Monument St., Baltimore, MD 21205 USA. Telephone: (410) 502-7038. Fax: (410) 955-0036. E-mail: gdiette@mail.jhmi.edu

We thank F. Dominici and L. Pham for their review of our statistical modeling methods.

This study was supported by grants from the U.S. Environmental Protection Agency (R82672401) , National Institute of Environmental Health Sciences (ES09606) , and National Heart, Blood, and Lung Institute (HL04266, HL076322, HL67850) .

The authors declare they have no competing financial interests.

Received 8 February 2008 ; accepted 23 July 2008.