Observation of a Rotterdam plume event during CINDI-3

Between 21 May and 24 June 2024, the third Cabauw Intercomparison of UV-Vis DOAS Instruments (CINDI-3) took place. In addition to conventional PANDORA and MAX-DOAS instruments, three imaging instruments participated: the IMPACT instrument from the University of Bremen, and SEMPAS and the NO2 camera from the Royal Belgian Institute for Space Aeronomy. While the first two instruments sweep a linear array of fibers to construct a hypercube of the scene, the NO2 camera is a native imager which builds a hypercube by scanning in the spectral domain. Still, these three instruments pursue the same objective of improving both the temporal and spatial resolution of NO2 measurements, enabling new applications such as monitoring ship emissions and urban pollution at a street-level scale.From 14 June until the conclusion of the CINDI-3 campaign, the three imagers were operated synchronously, thereby capturing both the temporal and spatial dynamics of the NO2 field in the direction of Rotterdam. This coordinated operation allows for a comparison between the differential slant column densities of the three imagers. On 17 June 2024, during the afternoon, an NO2 plume originating from the Port of Rotterdam was observed by all three imagers. The measurements acquired both prior to and during the plume event show good correlation among the instruments.Throughout the CINDI-3 campaign, daily NO2 forecasts were provided based on the E-PRTR emission database using the FLEXPART-WRF dispersion model based on dynamically-downscaled GFS forecast data. To provide further insight for the plume event on 17 June, an ensemble of simulations using different planetary boundary layer schemes was carried out based on downscaled GFS and ERA5 meteorological data. The simulated plume location and the horizontal SCDs show good agreement with the observational results from the imaging instruments.This contribution will highlight how a fortuitous event (the blowing of industrial pollution in the direction of the CINDI-3 campaign site) became an excellent test case for intercomparing non-conventional DOAS instruments, and how a plume dispersion model could both confirm the hypothesis of the distant plume origin and be validated by remote sensing instruments.