As part of a large panel study in Seattle, Washington, we measured levels of exhaled nitric oxide (eNO) in children's homes and fixed-site particulate matter with aerodynamic diameters of 2.5 µm or less (PM_2.5) outside and inside the homes as well as personal PM_2.5 during winter and spring sessions of 2000-2001. Nineteen subjects 6-13 years of age participated; 9 of the 19 were on inhaled corticosteroid (ICS) therapy. Exhaled breath measurements were collected offline into a Mylar balloon for up to 10 consecutive days. Mean eNO values were 19.1 (SD ± 11.4) ppb in winter sessions and 12.5 ± 6.6 ppb in spring sessions. Fixed-site PM_2.5 mean concentrations were 10.1 ± 5.7 µg/m³ outside homes and 13.3 ± 1.4 inside homes; the personal PM_2.5 mean was 13.4 ± 3.2 µg/m³. We used a linear mixed-effects model with random intercept and an interaction term for medications to test for within-subject-within-session associations between eNO and various PM_2.5 values. We found a 10 µg/m³ increase in PM_2.5 from the outdoor, indoor, personal, and central-site measurements that was associated with increases in eNO in all subjects at lag day zero. The effect was 4.3 ppb [95% confidence interval (CI), 1.4-7.29] with the outdoor monitor, 4.2 ppb (95% CI, 1.02-7.4) for the indoor monitor, 4.5 ppb (95% CI, 1.02-7.9) with the personal monitor, and 3.8 ppb (95% CI, 1.2-6.4) for the central monitors. The interaction term for medication category (ICS users vs. nonusers) was significant in all analyses. These findings suggest that eNO can be used as an assessment tool in epidemiologic studies of health effects of air pollution. Key words: airway inflammation, asthma, children, exposure assessment, inhaled corticosteroids, nitric oxide, panel study, personal exposure, PM_2.5. Environ Health Perspect 111:1625-1629 (2003). [Online 12 June 2003]

doi:10.1289/ehp.6160 available via http://dx.doi.org/