In this study, we propose a new principle for measuring atmospheric NO using a laser-induced fluorescence (LIF) NO 2 detector. NO is chemically converted into NO 2; then, NO 2 is detected by the LIF technique. To convert NO into NO 2, ozone is added to sample air. Since there exists un-reacted NO and loss of NO 2 due to further reaction of NO 2 with ozone depending on both the concentration of ozone and reaction time, the enhanced NO 2 concentration is less than the initial NO concentration. Using chemical kinetic analysis, we successfully derive the relationship between NO concentration and LIF signals. We also propose a unique calibration method for an LIF NO 2 detector without using a chemiluminescent NO x analyzer; this method is based on the gas phase titration technique. The limits of the detection of the developed instrument for NO 2 and NO measurements are 14 ppt and 22 ppt, respectively. We perform ambient air measurements in a suburb of Tokyo using the developed LIF NO analyzer and a commercial chemiluminescent NO analyzer. A comparison of the measurement results reveals that they are in excellent agreement, with a slope of 0.99 and a correlation coefficient of 0.99.