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The seasonal variability in the composition of PAHs and NPAHs in PM2.5 on the basis of the number of rings: (a) PAHs; (b)NPAHs. 4-ring PAHs: Flt, Pyr, BaA, Chr; 5-ring PAHs: BbF, BkF, BaP; 6-ring PAHs: BgPe, IDP; 3-ring NPAHs: 9-NA, 3-NPhe; 4-ring NPAHs: 1-NP, 7-NBaA; 5-ring NPAHs: 6-NBaP.
