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 including traffic, industrial, residential, commercial, and educational areas in Urumqi, a megacity in northwest China. Airborne PM10 and PM2.5 samples were collected from five functional areas during heating (November 2015 to March 2016) and non-heating (July 2016 to September 2016) periods, and 16 priority PAHs (Ʃ16PAHs) in the samples were quantified and analyzed. Over the study period, the average Ʃ16PAHs in PM10 and PM2.5 were 116.97 ± 41.44 ng m-3 and 88.57 ± 31.22 ng m-3, respectively. In the heating period, Ʃ16PAHs in both fractions were more than 2.5 times higher than those in the non-heating period, with the highest values found in the industrial area in the heating period and in the traffic area in the non-heating period. The northern part of the city had more PAH pollution than did the southern part. The compositions of particle-bound PAHs varied temporally and spatially, with 4-ring PAHs contributing more in the heating period than in 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, while 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 for both periods at traffic sites and central urban sites, while heavy-duty vehicle emissions and natural gas/biomass/coal combustion emissions dominated in the industrial area. The average Benzo[a]pyrene equivalent toxicity (BaPeq) ranged from 4.4-37.9 ng m-3, showing a generally similar spatiotemporal distribution with Ʃ16PAHs. The results showed that the lifetime excess cancer risk (LCR) in the heating period was higher than that in the non-heating period, and people who live around the industrial and traffic areas had more likelihood of getting lung cancer than residents in other parts of the city.