Figure 3.

(a) VOCs that were correlated with smoking status; (b) VOCs that were correlated with smoking intensity; (c) VOCs that were correlated with years of smoking; (d) VOCs that were correlated with depth of smoke inhalation. (* denotes p < 0.05, ** denotes p < 0.01; sign ∆ means this compound was correlated with smoking status, years of smoking, and depth of smoke inhalation in the meanwhile, and sign ▪ was both correlated with smoking intensity and depth of smoke inhalation, while sign ★ was both correlated with smoking status and depth of smoke inhalation).