Development of a Selective Light-Emitting Diode Photolytic NO2 Converter for Continuously Measuring NO2 in the Atmosphere

A photolytic converter of nitrogen dioxide (NO2) to nitric oxide (NO) using light-emitting diodes (LEDs) has been designed to measure NO2 in the troposphere. The typical electrical power consumption of the photolytic converter (PLC) is only 44 W. The maximum conversion efficiency of NO2 to NO of the photolytic converter is around 90%, which is higher than that of metal halides or high-pressure Xe arc lamps (up to ∼70%). The conversion efficiency of the PLC was almost constant for at least 2.5 months. The conversion efficiency of peroxyacetyl nitrate by the LED-PLC was measured to be 2.6 ± 0.1% (1σ). The interference of HONO using the PLC was experimentally estimated to be less than 3%, which is within the uncertainty of the instrument. An intercomparison of NO2 measurements between the PLC-CLD and the laser-induced fluorescence (LIF) technique was conducted, and the NO2 concentrations measured by the PLC-CLD method were in agreement with those obtained by the LIF technique, within the uncertainties of the instruments. Continuous observations were made on Fukue Island, a remote area. These results demonstrate the performance of the PLC for continuous ambient measurements.