An ultraweak chemiluminescence (CL) was observed when sodium hydrosulfite (NaHSO3) reacts with hydrogen peroxide (H2O2) and was enhanced 70 times by adding 10 pmol benzo[a]pyrene-7,10-quinone (7,10-BaPQ). The CL reaction is fast, and it reached maximum intensity in 0.1 s, and then decayed to baseline in 3 s. Mechanism of NaHSO3-7,10-BaPQH(2)O(2) system were investigated by CL spectrum, radical scavengers and electron spin resonance (ESR). Hydroxyl radical ((OH)-O-center dot), super oxide anion radical (O-center dot(2)-), and sulfite radical ((SO3-)-S-center dot) were generated in the NaHSO3-7, 10-BaPQ-H2O2 system. Reduction of 7,10-BaPQ by O-center dot(2)- radical gave excited semiquinone, which showed strong CL emission when decayed to its ground state. Maximum CL emission wavelength was located at 440 nm, which may belong to the excited semiquinone. This CL system was developed as post column detection of high performance liquid chromatography for the determination of 7,10-BaPQ Linearity ranged from 50 fmol to 20 pmol (R-2 = 0.9995) with limit of detection of 30 fmol (S/N = 3). The proposed method was used to determine 7,10-BaPQ in airborne particulates. Average atmospheric concentrations of 7,10-BaPQ in Kanazawa in December 2010 and Wajima in October 2007 were 2.0 and 1.6 pg/m(3), respectively.