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 NOx 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.