Indexed on: 29 May '18Published on: 29 May '18Published in: Optics express
An inexpensive, compact instrument for sensitive measurement of nocturnal nitrogen oxides NO and NO in ambient air at high time resolution has been described. The instrument measures NO and NO which is converted into the NO radical through thermal decomposition by optical extinction using a diode laser at 662.08 nm in two separate detection channels. The minimum detection limits (1σ) for the NO radical and NO are estimated to be 2.3 pptv and 3.1 pptv in an average time of 2.5 s, with the accessible effective absorption path length generally exceeding 30 km, which is sufficient for quantifying NO radical and NO concentrations under moderately polluted conditions. The total uncertainties of the NO and NO measurements are 8% and 15% respectively, which are mainly dominated by the uncertainty of NO across section calculated for 353 K in this system. In addition, the dependence of the instrument's sensitivity and accuracy on a variety of conditions was presented in winter of 2016 and in summer of 2017 during two China-UK joint campaigns. Distinct NO vertical profiles were observed at night in winter. The equilibrium among observed NO, NO and NO based on the equilibrium constants during summer time also provides confirmation of the measurement accuracy of the instrument.