Air-pollutants linked to shipping emissions observed in the North of France in July 2023 during the Aero-HdF campaign

Aerosols originate from diverse sources, which determine their physical, chemical and optical properties, and influence both climate and clouds. Fine submicron particles are particularly hazardous; mostly linked to air pollution, they can penetrate deep into the human respiratory system and bloodstream, posing a significant health risk.The AERO-HDF airborne campaign was conducted in July 2023 over the North of France, the English Channel, and the North Sea; a region characterized by dense shipping traffic. During the mission, a series of scientific flights utilized in situ instruments onboard the SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) ATR 42 research aircraft to measure the size and optical properties of atmospheric particles using the AVIRAD sampling system, as well as gas concentrations. Additionally, remote sensing data were collected for the same air masses using OSIRIS (Observation System Including Polarisation in the Solar Infrared Spectrum), the airborne simulator for newly launched spaceborne 3MI (Multi-viewing Multi-channel Multi-polarisation Imager) satellite sensor. Atmospheric particles were also sampled to study their chemical composition, morphology and mixing state.First, our measurements reveal that, in the marine boundary layer, aerosols displayed significant light absorption. They were predominantly externally mixed, and characterised by a dominant mode of particles below 100 nm in diameter and a fine mode mostly consisting in organic aerosols. Multiple passes at very low altitude measured an aerosol Single Scattering Albedo (SSA) of 0.85-0.80 at 630 nm in a fresh ship plume, significantly lower than in the background air (SSA=0.90). These fresh emissions were also accompanied by elevated levels of NOx​, SO2​, and water vapour. Traces of amorphous carbon, a signature profile of diesel ship engines, were also detected. Finally, a chemical transport model model (WRF-CHIMERE) was used to model aerosols and gases. We will present comparisons between the model results, in situ data, and polarimeter retrievals. Potentially, we will share preliminary findings regarding the impact of these pollutants on cloud formation.