Development of atmospheric NO analyzer by using a laser-induced fluorescence NO₂ detector

In this study, we propose a new principle for measuring atmospheric NO using a laser-induced fluorescence (LIF) NO₂ detector. NO is chemically converted into NO₂; then, NO₂ is detected by the LIF technique. To convert NO into NO₂, ozone is added to sample air. Since there exists un-reacted NO and loss of NO₂ due to further reaction of NO₂ with ozone depending on both the concentration of ozone and reaction time, the enhanced NO₂ 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 NO₂ 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 NO₂ 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.