Intensive daytime and nighttime sampling was carried out from 23 Oct to 31 Dec 2008 to investigate the occurrence of nitrated polycyclic aromatic hydrocarbons (NPAHs) in PM10 at a roadside site in Xiamen,China.At the same time,six PM10 samples were collected from a nearby roadway tunnel for comparison.Six NPAHs,namely 9-nitroanthracene,2- and 3-nitrofluoranthene,1-nitropyrene,7-nitrobenz[a]anthracene,and 6-nitrobenzo[a]pyrene,were identified and quantified using GC/MS in negative ion chemical ionization mode.The average total concentration of six NPAHs (ΣNPAHs) in the cold season (26 Nov-31 Dec) was 2.3 (daytime) and 9.9 (nighttime) times higher than those in the warm season.Significant statistical difference (p ＜ 0.01,2-tailed) of ΣNPAHs between daytime and nighttime was found during both the warm and cold seasons.NPAHs were significantly positively correlated with their parent PAHs and nitrogen dioxide but negatively correlated with ambient temperature.The ratio of 2 + 3-nitrofluoranthene to 1-nitropyrene exhibited a similar diurnal pattern as ΣNPAHs and was generally greater than 5,indicating the importance of secondary atmospheric formation.The diurnal variations of NPAHs were all influenced by the diurnal variations of PAHs,nitrogen dioxide,sunlight,and temperature.The dally inhalable exposure to the six NPAHs in the tunnel was much higher than the roadside values in the warm season but only slightly higher than those in the cold season.