Associations of PM2.5 carbonaceous and ionic constituents with fractional exhaled nitric oxide (FeNO): A panel study with 16 follow-up visits over 4 years.

Epidemiological studies have linked fine particulate matter (PM2.5) to elevated fractional exhaled nitric oxide (FeNO), biomarker of airway inflammation. However, the specific roles of PM2.5 chemical components remain underexplored. This panel study examined relationships between temperature-resolved carbon subfractions or ionic components of PM2.5 and FeNO. A cohort of 69 self-reported healthy undergraduate students was followed 16 times between 2014 and 2018. PM2.5 samples were collected from the roof of a campus building, while carbonaceous and ionic components were quantified using a carbon analyzer and ion chromatography. Confounder-adjusted linear mixed-effects models were used to evaluate the influence of single-day and cumulative lag exposures. The constituent's residual model was employed to perform additional adjustment for PM2.5's effect on other chemical constituents. Mixed-component effects were evaluated using a Bayesian kernel machine regression (BKMR) model. We observed significant increases in FeNO levels associated with interquartile range (IQR) increases in cumulative exposure to EC3 (1.52 %, lag 5 days), Na+ (20.61 %, lag 4 days), K+ (15.13 %, lag 2 days), C2O42- (1.70 %, lag 5 days), F- (2.44 %, no lag), Cl- (11.52 %, lag 3 days), with carbonaceous fractions showing impacts at 2-3-day lags. Effect estimates were larger in males for pollutants including Ca2+, F-, EC2, and EC3 compared with females. These findings indicate that FeNO is associated with specific carbonaceous and ionic PM2.5 components, with potential sex differences in susceptibility. The results strengthen evidence linking PM2.5 components to airway inflammation and underscore their role in amplifying the adverse health impacts of air pollution.