Observations of N2O5 in the Remote Atmosphere during ATom-2

N₂O₅ is potentially an important reservoir of NO_x (NO_x = NO + NO₂) in the remote atmosphere. However, to date most measurements of N₂O₅ have been performed in polluted atmospheres at lower altitudes. During the ATom-2 deployment a thermal decomposition-chemical ionization mass spectrometer (TD-CIMS) using iodide as a reagent ion was deployed to measure PAN. This also gave the opportunity to measure the sum of NO₃ and N₂O₅, which during the day is expected to be dominated by N₂O₅. Preliminary analysis and calibrations indicate that N₂O₅ was less than 20 pptv for almost all flight conditions. However, an interference to this measurement at high ozone levels was observed in stratospheric air. This degraded the detection limit of this method at high altitude. Here we will present the observed distributions of N₂O₅ and compare them to those predicted by a global model. We will also present our analysis of the mechanism for the ozone interference to the iodide CIMS detection of N₂O₅ and other species.