Associations between outdoor air pollution, ambient temperature and fraction of exhaled nitric oxide (FeNO) in university students in northern China - A panel study

Background: Northern China has severe air pollution, especially in winter. Fractional exhaled nitric oxide (FeNO) is an established biomarker of airway inflammation. Aim: To study associations between ambient temperature, air pollution and FeNO in university students in northern China. Methods: We performed a panel study in 67 university students without asthma diagnosis in the city of Taiyuan. FeNO was measured 6 times, over one heating season. Outdoor PM10, PM2.5, SO2, NO2 and O-3 were measured at a fixed location in the campus. SO2, NO2 and O-3 were measured 7 days (24 h/day) before the FeNO test. PM2.5 and PM10 were measured at different lag times (lag 1 day to lag 7 days). Temperature and carbon monoxide (CO) data were collected from a nearby monitoring station (lag 7). Linear mixed models were applied to study associations between exposure and FeNO, adjusting for gender, age, current smoking, height and furry pet or pollen allergy. Results: The overall geometric mean (GM) of FeNO was 17.2 ppb. GM of FeNO was lowest (12.9 ppb) in January and highest (20.0 ppb) in April. The range of lag 7 pollution was 105.0-339.0 mu g/m(3) for PM10, 72.0-180.0 mu g/m(3) for PM2.5, 36.0-347.0 mu g/m(3) for SO2, 26.0-69.0 mu g/m(3) for NO2, 31.0-163.0 mu g/m(3) for O-3 and 0.93-3.14 mg/m(3) for CO. The lag 7 temperature ranged from -4.5 to 20.1 degrees C. FeNO was consistently higher at higher outdoor temperature (p < 0.001). In multi-pollutant models with temperature adjustment, PM10, PM2.5 and SO2 were associated with FeNO (all p-values <0.001). In contrast, CO was negatively associated (protective) with FeNO (p < 0.001). Associations between exposure and FeNO were similar in men and women. Conclusion: PM10, PM2.5 and SO2 and outdoor temperature can be associated with airway inflammation, measured as FeNO, in young adults in northern China while CO could be negatively associated with FeNO