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Background Ambient fine particulate matter (PM 2.5 ) air pollution has been associated with increased airway inflammation, but the roles of various PM 2.5 constituents remain to be determined. Objectives To investigate the acute effects of PM 2.5 constituents on fractional exhaled nitric oxide (FeNO), a well-established biomarker of respiratory inflammation. Methods A longitudinal panel study was performed among 32 healthy young adults in Shanghai, China from January 12th to February 6th, 2015. FeNO was repeatedly measured, 6–8 times per subject. Real-time mass concentration of ambient PM 2.5 and chemical constituents were obtained from a nearby monitoring station. Linear mixed-effect models were applied to evaluate the association between FeNO and PM 2.5 constituents, with the adjustment of age, gender, body mass index, temperature, relative humidity and day of week. The robustness of constituents’ effects was also evaluated. Results A total of 234 effective measurements of FeNO were obtained with a geometric mean of 13.1 ppb. The PM 2.5 -FeNO associations were strongest at lags of 0–6 h and diminished at lags longer than 12 h. An interquartile range increase in PM 2.5 constituents (NH 4 + , NO 3 − , K + , SO 4 2− and elemental carbon) at lags of 0–6 h were significantly associated with increments in FeNO by 12.3%, 11.3%, 11.1%, 9.6% and 10.7%, respectively. After controlling for PM 2.5 total mass and the colinearity, only elemental carbon remained significant. Conclusion Several chemical constituents of PM 2.5 may impact FeNO following acute exposure. Elemental carbon in particular may be the primary component responsible for increased airway inflammation. [ABSTRACT FROM AUTHOR]