In-injection port thermal desorption (TD) was extended in determination of particulate phase nitrated-polycyclic aromatic hydrocarbons (N-PAHs) on filter samples coupled with a gas chromatography/negative ion chemical ionization-mass spectrometry (GC/NCI-MS). The experimental and analytical parameters were optimized with standard testing and ambient samples. Fourteen of the most abundant N-PAHs in ambient airs were included for their quantification. A desorption temperature of 280 °C for 10 min was sufficient to transfer entire target compounds from injection port to the analytical system. Good linearity (R2 >0.995) on the calibrations for each analyte was achieved. The limit of detections (LODs) ranged from 46.5 to 152.3 pg per filter sample, which were 4–66% better than solvent extraction (SE) approach. Method precision, repeatability and reproducibility, determined by replicate analyses of calibration standards and ambient samples, were less than 6% for target compounds. Validation of the method were conducted with two batches of a total of 30 ambient aerosol-loaded filters using our TD and the traditional SE approaches. Reasonably good agreement (R2 = 0.98) by the two methods was demonstrated for most of N-PAHs, except for 9-nitrophenanthrene and 6-nitrobenzo(a)pyrene. The in-injection port TD can improve laboratory efficiency and reduce solvent-based costs for the measurement of N-PAHs.