This study concentrated on the pollution level, sources, and lung cancer risk of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) in spring in Nanjing, China. The PM2.5 samples were collected in spring of the year 2016 in Nanjing. Sixteen United States Environmental Protection Agency priority PAHs were extracted and analyzed after sampling. The mean concentrations of PAHs and BaPeq were 3.98 ± 1.01 and 0.29 ± 0.08 ng/m3, respectively, which is a low level among results from regions worldwide. The diurnal variations of PAHs and BaPeq concentrations showed a relatively high level in the early morning, at the morning rush time of work and traffic transportation, and in the evening traffic peak hours. According to the results of diagnostic ratios, PAHs originated mainly from traffic exhaust, especially diesel vehicle emissions. In a single day, the highest inhalation exposure level was focused between 4 a.m. and 6 a.m., whereas the time between 12 a.m. to 2 p.m. in a day had the lowest exposure dose. Due to the inhalation exposure, the median values of incremental lung cancer risk in spring were estimated to be 7.08 × 10-9, 5.29 × 10-9, 3.53 × 10-8, 5.21 × 10-9, 7.21 × 10-9, 5.24 × 10-9, 3.01 × 10-8, and 5.40 × 10-9 for boys, male adolescents, male adults, male seniors, girls, female adolescents, female adults, and female seniors, respectively, indicating low potential lung cancer risk.