To improve our current understanding of the fate of particle-bound PAHs, which include potent mutagens and carcinogens, diurnal measurements of these compounds were carried out from 23 Oct to 31 Dec 2008 at a busy traffic site in Xiamen, China. The sum of 19 PAH concentrations showed a just noticeable day-night difference in the warmer period (from 23 Oct to 25 Nov) to a remarkable day-night difference in the colder period (from 26 Nov to 31 Dec). However, the average profiles of the 19 PAHs in the warmer and colder periods were very similar for both day and night samples. Atmospheric mixing seemed to have more influence on the diurnal variations in PAHs than photodecomposition resulting from solar radiation, because PAH concentrations showed negative correlation with air temperature but significantly positive correlation with the ratios of reactive to stable PAHs, such as benz[a]anthracene to chrysene and benzo[a]pyrene to benzo[e]pyrene. Based on the diagnostic ratios of indeno[1,2,3-cd]pyrene to indeno[1,2,3-cd]pyrene plus benzo[g,h,i]perylene and fluoranthene to fluoranthene plus pyrene, the results showed that no significant differences were observed in PAHs sources between the warm and cold periods and a combination of grass, wood or coal combustion and petroleum sources in airborne particles might be the most significant contributors of PAHs. Gas-phase PAHs were calculated based on the theoretical gas/particle partitioning coefficients for 19 PAHs and a high fraction of daily exposure was attributed to particle-phase PAHs in most cases. The excess lifetime cancer risk in colder period was generally higher than in the warmer period. The total uncertainties were computed based on the simpler average error transfer formula.