In this work, we developed an alternative calibration method for measuring N 2 O 5 with an iodide adduct mass spectrometer (I-CIMS). In this calibration method, N 2 O 5 is heated and then quantified based on the decrease in the amount of NO due to its reaction with the pyrolysis product (NO 3 ). This alternative calibration method was compared with the commonly used method utilizing NO x analyzers equipped with a photolytic converter, which gauge NO 2 reduction as a result of its reaction with O 3 to quantify N 2 O 5 . It is notable that the two methodologies demonstrate favorable consistency in terms of calibrating N 2 O 5 , with a variance of less than 10 %. The alternative calibration method is a more reliable way to quantify N 2 O 5 with CIMS, considering the instability of the NO 2 conversion efficiency of photolytic converters in NO x analyzers and the loss of N 2 O 5 in the sampling line. The effects of O 3 and relative humidity (RH) on the sensitivity toward N 2 O 5 were further examined. There was minimal perturbation of N 2 O 5 quantification upon exposure to O 3 even at high concentrations. The N 2 O 5 sensitivity exhibited a nonlinear dependence on RH as it initially rose and then fell. Besides I(N 2 O 5 ) - , the collisional interaction between I(H 2 O) - and N 2 O 5 also forms I(HNO 3 ) - , which may interfere with the accurate quantification of HNO 3 . As a consequence of the pronounced dependence on humidity, it is advisable to implement humidity correction procedures when conducting measurements of N 2 O 5 .