Air pollution exposure was found to be associated with chronic bronchitis (chronic cough and sputum production) in a recent study by researchers at the University of Washington. The study was conducted on the large Sisters Study cohort (about 50,000 participants), limiting analysis to never-smokers, and using exposure models to PM10, PM2.5, and NO2 developed for the MESA Air Study. Association of chronic bronchitis prevalence (i.e. existing cases) were observed for PM10 (odds ratio of 1.07 per increase of interquartile range, 5.8 mg/m3). Associations were also observed for PM2.5 with prevalence of chronic bronchitis (OR 1.18); and for NO2 with prevalence of chronic bronchitis (OR of 1.10), cough (OR of 1.10), and phlegm (OR of 1.07). No associations were observed for incidence (i.e. new cases) of these respiratory problems, but the authors observe that the limited follow-up time (<6 years) did not offer sufficient power for that analysis, compared to effect prevalence. The effects reported were independent of each other, and the authors believe this is the first reported observation of an independent association of PM10 with chronic bronchitis. These results may be relevant to PM10 and multi-pollutant policy.