Validation of HNO₃, CIONO₂, and N₂O₠from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS)

Overall the quality of the ACE-FTS v2.2 HNO₃ VMR profiles is good from 18 to 35 km. For the statistical satellite comparisons, the mean absolute differences are generally within ±1 ppbv (±20%) from 18 to 35 km. For MIPAS and MLS comparisons only, mean relative differences lie within ±10% between 10 and 36 km.

ACE-FTS HNO₃ partial columns (~15-30 km) show a slight negative bias of -1.3% relative to the ground-based FTIRs at latitudes ranging from 77.8° S-76.5° N. Good agreement between ACE-FTS CIONO₂ and MIPAS, using the Institut für Meteorologie und Klimaforschung and Instituto de Astrofísica de Andalucía (IMK-IAA) data processor is seen. Mean absolute differences are typically within ±0.01 ppbv between 16 and 27 km and less than +0.09 ppbv between 27 and 34 km.

The CIONO₂ partial column comparisons show varying degrees of agreement, depending on the location and the quality of the FTIR measurements. Good agreement was found for the comparisons with the midlatitude Jungfraujoch partial columns for which the mean relative difference is 4.7%. ACE-FTS N₂O₠has a low bias relative to MIPAS IMK-IAA, reaching -0.25 ppbv at the altitude of the N₂O₠maximum (around 30 km).

Mean absolute differences at lower altitudes (16-27 km) are typically -0.05 ppbv for MIPAS nighttime and ±0.02 ppbv for MIPAS daytime measurements.