Molecular diagnostic ratios (MDRs) have been widely used to investigate PAH sources [35–37]. The most commonly used ratios include Ant/(Ant + Phe), BaA/(BaA + Chr), Flt/(Flt + Pyr) and IcdP/(Icdp +BghiP) [36]. Some studies have highlighted that atmospheric sources can be mixed and can complex in real-world settings and that individual PAH compounds have different atmospheric residence times and reactivities [38–40]. Previous studies have also questioned the efficiency of these MDRs [38–43]. Because the large petrochemical complex was the only significant pollution source in the sampling site, the atmosphere measurements were performed close to the known specific source. Therefore, the efficiencies of these MDRs could be well tested in this study.