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Therese F. Mar,¹ Karen Jansen,¹ Kristen Shepherd,² Thomas Lumley,² Timothy V. Larson,³ and Jane Q. Koenig¹

¹Department of Environmental Health and Occupational Sciences, ²Department of Biostatistics, and ³Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA

Abstract
The objective of this study was to evaluate associations between short-term (hourly) exposures to particulate matter with aerodynamic diameters < 2.5 µm (PM_2.5) and the fractional concentration of nitric oxide in exhaled breath (Fe_NO) in children with asthma participating in an intensive panel study in Seattle, Washington. The exposure data were collected with tapered element oscillation microbalance (TEOM) PM_2.5 monitors operated by the local air agency at three sites in the Seattle area. Fe_NO is a marker of airway inflammation and is elevated in individuals with asthma. Previously, we reported that offline measurements of Fe_NO are associated with 24-hr average PM_2.5 in a panel of 19 children with asthma in Seattle. In the present study using the same children, we used a polynomial distributed lag model to assess the association between hourly lags in PM_2.5 exposure and Fe_NO levels. Our model controlled for age, ambient NO levels, temperature, relative humidity, and modification by use of inhaled corticosteroids. We found that Fe_NO was associated with hourly averages of PM_2.5 up to 10-12 hr after exposure. The sum of the coefficients for the lag times associated with PM_2.5 in the distributed lag model was 7.0 ppm Fe_NO. The single-lag-model Fe_NO effect was 6.9 [95% confidence interval (CI) , 3.4 to 10.6 ppb] for a 1-hr lag, 6.3 (95% CI, 2.6 to 9.9 ppb ) for a 4-hr lag, and 0.5 (95% CI, -1.1 to 2.1 ppb) for an 8-hr lag. These data provide new information concerning the lag structure between PM_2.5 exposure and a respiratory health outcome in children with asthma. Key words: airway inflammation, asthma, children, exhaled nitric oxide, particulate matter less than or equal to 2.5 µm, short-term exposure. Environ Health Perspect 113: 1791-1794 (2005) . doi:10.1289/ehp.7883 available via http://dx.doi.org/ [Online 8 August 2005]

Address correspondence to J.Q. Koenig, Department of Environmental Health and Occupational Sciences, Box 357234, Room F561a, University of Washington, Seattle, WA 98195-7234 USA. Telephone: (206) 543-2026. Fax: (206) 685-3990. E-mail: Jkoenig@u.washington.edu

This work was funded by the U.S. Environmental Protection Agency (EPA) (CR82717701) , the Northwest Research Center for Particulate Air Pollution and Health (EPA grant CR827355) , and National Institute for Environmental Health Sciences grant P30 ES07033.

This report has been subjected to agency review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.

The authors declare they have no competing financial interests.

Received 21 December 2004 ; accepted 8 August 2005.

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