CINDI-3 Campaign: Global Efforts in Air Pollution Measurement and Validation

The Institute of Natural Sciences and the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) recently participated in the third “Cabauw Intercomparison of UV-Vis DOAS Instruments” (CINDI-3). This campaign took place in May-June 2024 and was organized by the Royal Netherlands Meteorological Institute (KNMI) at the Cabauw observatory, located between Rotterdam and Utrecht. More than 100 persons from 16 countries, with 44 instruments, were involved in the international measurement campaign, the largest of its kind in the world.

The main purpose of CINDI-3 is to test and compare different MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) instruments that measure air pollutants such as nitrogen dioxide (NO₂) and ozone (O₃). These instruments use a technique that analyses the spectrum of scattered sunlight to determine the presence and concentration of various gases in the atmosphere.

As part of the Belgian contribution, the aerial surveillance aircraft of the Institute of Natural Sciences was equipped with various measuring instruments in the weeks before the exercise (including the BIRA SWING imaging DOAS system), while BIRA also supplied NO₂ and O₃ in-situ measuring equipment. Together with other measuring devices near the KNMI measuring mast in Cabauw, and operated on cars and bicycles, a complete picture of the distribution of pollutants in the industrial and urban areas around Rotterdam could be compiled. The NO₂ distribution over Antwerp was also mapped from the aircraft as part of the same campaign.

All flights were carried out in synchronisation with the Copernicus Sentinel-5 Precursor satellite that carries the ESA TROPOMI instrument (Tropospheric Monitoring Instrument). This instrument maps various air quality and climate parameters. Thanks to the successful comparison of the observations of the measuring instruments on board the aircraft and on the ground, they can serve as a reliable reference for validating satellite instruments that measure air pollution from space.