The purpose of the present study was to evaluate the polycyclic aromatic hydrocarbons (PAHs) in fine (PM2.5) and coarse (PM10) particles in five functional areas, namely, the traffic, industrial, residential, commercial, and educational areas, in Urumqi, a megacity in northwest China. Airborne PM10 and PM2.5 samples were collected from the five areas during heating (November 2015–March 2016) and non-heating (July–September 2016) periods, and 16 priority PAHs (Ʃ16PAHs) in the samples were quantified and analyzed. Over the study period, the average Ʃ16PAHs in the PM10 and PM2.5 were 116.97 ± 41.44 ng m–3 and 88.57 ± 31.22 ng m–3, respectively. During the heating period, Ʃ16PAHs in both of the fractions were more than 2.5 times those during the non-heating period, with the highest values found in the industrial area during the heating period and in the traffic area during the non-heating period. The northern part of the city had more PAH pollution than the southern part. The compositions of the particle-bound PAHs varied temporally and spatially, with 4-ring PAHs contributing more during the heating period than during the non-heating period and with 5- and 6-ring PAHs exhibiting the opposite trend. In addition, 4-ring PAHs contributed more in the industrial area, whereas 5- and 6-ring PAHs contributed more in the traffic area, reflecting the variety of emission sources. Principal component analysis and diagnostic molecular ratios showed that vehicular exhaust was the major source of PAHs during both periods at the traffic and central urban sites, while heavy-duty vehicular emissions and natural gas/biomass/coal combustion emissions dominated in the industrial area. The average Benzo[a]pyrene equivalent toxicity (BaPeq) ranged from 4.4 to 37.9 ng m–3, showing a generally similar spatiotemporal distribution with the Ʃ16PAHs. The results showed that the lifetime excess cancer risk (LCR) during the heating period was higher than during the non-heating period and that people who lived around the industrial and traffic areas had a higher likelihood of getting lung cancer than residents in other parts of the city.