14 that of PAHs depending on ring numbers. In this report, abbreviations are used for major PAHs and their derivatives. Please refer to the list of abbreviations at the end of this report. Their chemical structures are shown in Fig. 1. 2.2 Distribution in Ambient Air PAHs and their derivatives are ubiquitous in both indoor and outdoor air. As described above, lower- molecular-weight PAHs exist in gaseous form. Likewise, higher-molecular-weight PAHs exist mainly as fine PM with an aerodynamic diameter of less than or equal to a nominal 2.5 µm (PM2.5). The distribution of their derivatives has similar tendencies. Fig. 2 shows concentrations of major PM2.5-bound PAHs, NPAHs, OHPAHs and QPAHs measured in urban air in Kanazawa, Japan. Although the concentration levels of the derivative groups differ greatly, the concentration order shows the same trend between urban and suburban air and between Abbreviations, see list of abbreviation. Fig. 1 Chemical structures of PAHs, NPAHs, OHPAHs and QPAHs. K. HAYAKAWA vehicular and other combustion emissions (Hayakawa et al., 2020]. As can be seen in Fig. 2, the concentrations of total PAHs (ΣPAH), NPAHs (ΣNPAH), OHPAHs (ΣOHPAH), and QPAHs (ΣNOPAH) in Kanazawa City were 1000 pg m-3, 9.6 pg m-3, 75 pg m-3 and 420 pg m-3, respectively, with [ΣPAH] > [ΣQPAH] > [ΣOHPAH] > [ΣNPAH] in decreasing order. Among these compounds, pyrene (Pyr), benz[a]anthracene (BaA) and benz[a]pyrene (BaP) are the PAHs whose derivatives were commonly detected in the NPAHs, OHPAHs and QPAHs. For example, three isomers were respectively detected as pyrene-quinones (PyrQs). The concentration order of Pyr derivatives, quinoid pyrenes (QPyrs), hydroxypyrenes (OHPyrs) and nitropyrenes (NPs), were [Pyr] > [QPyrs] > [OHPyrs] > [NPs]. The derivatives of BaA and BaP also showed the same decreasing order described above. These results suggest that the order of concentrations of PAHs and their derivatives mainly depends on how easily the PAHs are derived in the combustion of organic matter.

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