Indoor/outdoor relationships, sources and cancer risk assessment of NPAHs and OPAHs in PM2.5 at urban and suburban hotels in Jinan, China

Paired indoor and outdoor measurements of 16 NPAHs and 5 OPAHs in PM2.5 were conducted at urban and suburban sites during January 2016 in Jinan, China. The concentrations of both indoor and outdoor NPAHs and OPAHs were higher at the urban site compared with the suburban site. 9N-ANT (16-42%), 2+3N-FLA (15-51%), 2N-PYR (6-20%), and 1N-PYR (4-6%) were the dominant NPAHs at all sites, and 9-FO (61-81%) was the most abundant OPAHs. Solid fuel combustion, motor vehicle exhausts, and secondary generation were the main sources of the PAH derivatives in this study area. The I/O ratios of 90% of NPAHs and OPAHs at the first urban indoor site (abbreviated as URI1, Green Tree Inn) and the suburban indoor site (abbreviated as SUI, the Seven Star Hotel) were <1.00 indicating that many of the compounds measured indoors originated from outdoor sources. At the second urban indoor site (abbreviated as URI2, Shandong University Hotel), the I/O ratios of 2- and 3-ring NPAHs and OPAHs were >1.00, which was likely due to cooking activities occurring near the measurement site. Measurements of outdoor 2+3N-FLA/1N-PYR revealed mainly primary emission at the urban site and secondary sources at the suburban site, the average ratios were 3.76 and 12.22, respectively. The average ratio of 2+3N-FLA/2N-PYR at all sites was 3.3, indicating that the OH-initiated reaction was the dominant secondary formation pathway. Nighttime ratios of 2+3N-FLA/1N-PYR were significantly higher than the daytime ratios at all sites. The difference was especially pronounced during heavily polluted conditions at the suburban site, which suggests that heavy pollution and nighttime conditions promote secondary production. Additionally, the cancer risk was highest in urban outdoor (abbreviated as URO) when the population expose to the level as the outdoor air in the urban. The risk suggested that adults may be at a higher cancer risk.