CYP1A1 and pulmonary arterial hypertension: Because of the higher contribution rates of smoking on 2-NAP and 9-PHE, we chose 1-OHP and 2-FLU as biomarkers of urine PAH metabolites to explore the co-exposure effect of smoking and occupational PAH on CYP1A1 hypomethylation and high 8-OHdG.