A new method for measuring gas-phase naphthalene in the atmosphere is based on laser-induced fluorescence at low pressure. The fluorescence spectrum of naphthalene near 308 nm was identified. Naphthalene fluorescence quenching by N₂, O₂ and H₂O was investigated in the laboratory. No significant quenching was found for H₂O with mixing ratio up to 2.5%. The quenching rate of naphthalene fluorescence is (1.98±0.18)×10^−11 cm³ molecule^−1 s^−1 for N₂, and (2.48±0.08)×10^−10 cm³ molecule^−1 s^−1 for O₂ at 297 K. Instrument calibrations were performed with a range of naphthalene mixing ratios between 5 and 80 parts per billion by volume (ppbv, 10^−9. In the current instrument configuration, the detection limit is estimated to be about 20 parts per trillion by volume (pptv, 10^−12) with 2σ confidence and a 1-min integration time. Measurement of atmospheric naphthalene in three cities, Nashville, TN, Houston, TX, and New York City, NY, are presented. Good correlation between naphthalene and major anthropogenic pollutants is found.