Third Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-3)

The third Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments took place at the Cabauw Atmospheric Research Station from 21 May until 24 June 2024. Cabauw is one of the main facilities of the Dutch Ruisdael Observatory located midway between the cities of Rotterdam and Utrecht, and managed by KNMI. Over 100 researchers from 18 countries worldwide participated in CINDI-3, operating 32 UV-VIS DOAS instruments to compare and intercalibrate measurements of air pollutants and to support the validation of earth observation satellite measurements from space-borne instruments such as Sentinel-5p/TROPOMI and Sentinel-4 and Sentinel-5. CINDI-3 is the third intercomparison campaign of this kind. The overall campaign planning and coordination was carried out by a steering committee, led by BIRA-IASB (Royal Belgian Institute for Space Aeronomy) and KNMI, coordinating the CINDI-3 intercomparison schedule and all additional activities such as the mobile and aircraft observations. The main science objectives of CINDI-3 are the following:

• To assess the consistency of slant column measurements of several key target species (NO2, ozone, O2-O2 and HCHO) of relevance for the validation of S5P and the future ESA atmospheric Sentinels, through coordinated operation of a large number of DOAS and MAXDOAS instruments from all over the world.
• To study the relationship between remote-sensing column- and profile-measurements of NO2, HCHO and ozone and reference in-situ concentration measurements of the same species.
• To investigate the horizontal representativeness of MAXDOAS measuring systems in view of their use for the validation of satellite tropospheric measurements featuring ground pixel areas in the range of 25-50 km2.