An Alternative Calibration Method for Measuring N 2 O 5 with an Iodide-Chemical Ionization Mass Spectrometer and Influencing Factors

In this work, we developed an alternative calibration method for measuring N O with an iodide adduct mass spectrometer (I-CIMS). In this calibration method, N O is heated and then quantified based on the decrease in the amount of NO due to its reaction with the pyrolysis product (NO ). This alternative calibration method was compared with the commonly used method utilizing NO analyzers equipped with a photolytic converter, which gauge NO reduction as a result of its reaction with O to quantify N O . It is notable that the two methodologies demonstrate favorable consistency in terms of calibrating N O , with a variance of less than 10 %. The alternative calibration method is a more reliable way to quantify N O with CIMS, considering the instability of the NO conversion efficiency of photolytic converters in NO analyzers and the loss of N O in the sampling line. The effects of O and relative humidity (RH) on the sensitivity toward N O were further examined. There was minimal perturbation of N O quantification upon exposure to O even at high concentrations. The N O sensitivity exhibited a nonlinear dependence on RH as it initially rose and then fell. Besides I(N O ) , the collisional interaction between I(H O) and N O also forms I(HNO ) , which may interfere with the accurate quantification of HNO . As a consequence of the pronounced dependence on humidity, it is advisable to implement humidity correction procedures when conducting measurements of N O .