Science Update: Chemical ionization mass spectrometry measurements of low-ppm mixing ratios of water vapour in the UTLS

T.D. Thronberry and co-authors use a chemical ionization mass spectrometer (CIMS) instrument to measure low water vapour mixing ratios in the upper troposphere/lower stratosphere (UTLS). The instrument performed well during 7 different flights, measuring water vapour mixing ratios as low as 3.5ppm near the tropopause. Measurement uncertainty was estimated between 9-11%. Find the full abstract here.