An Alternative Calibration Method for Measuring N₂O₅ with an Iodide-Chemical Ionization Mass Spectrometer and...

Area of Science:

• Atmospheric Chemistry
• Analytical Chemistry
• Mass Spectrometry

Background:

• Dinitrogen pentoxide (N₂O₅) is a key atmospheric species influencing air quality and climate.
• Accurate quantification of N₂O₅ is crucial for atmospheric modeling.
• Existing calibration methods for N₂O₅ using iodide adduct mass spectrometry (I-CIMS) have limitations.

Purpose of the Study:

• To develop and validate an alternative calibration method for N₂O₅ measurements using I-CIMS.
• To compare the performance of the new method with a conventional calibration technique.
• To investigate the influence of ozone (O₃) and relative humidity (RH) on N₂O₅ quantification.

Main Methods:

• Developed an alternative calibration method based on the reaction of N₂O₅ pyrolysis products (NO₃) with nitric oxide (NO).
• Quantified N₂O₅ by measuring the decrease in NO.
• Compared the new method with a standard method using NO₂ analyzers with photolytic converters and O₃.
• Examined the effects of O₃ and RH on N₂O₅ sensitivity.

Main Results:

• The alternative calibration method showed favorable consistency with the conventional method, with less than 10% variance.
• The new method is more reliable due to the instability of photolytic converters and potential N₂O₅ loss in sampling lines.
• N₂O₅ quantification showed minimal perturbation by O₃.
• N₂O₅ sensitivity exhibited a non-linear dependence on RH, necessitating humidity correction.

Conclusions:

• The developed alternative calibration method provides a more reliable approach for quantifying N₂O₅ using I-CIMS.
• Humidity correction is essential for accurate N₂O₅ measurements due to its significant impact on sensitivity.
• The formation of I(HNO₃)^- may interfere with nitric acid (HNO₃) quantification.