Multi-instrument characterization of distinct sequential aerosol patterns at Puy de Dôme Mountain observatory, France: outcomes from the RACLET field campaign

Organic and biological aerosols represent an important fraction of atmospheric particles, with identified impacts on atmopsheric physics and cloud processes (e.g., ice nucleation, chemical reactivity) and air quality. The RACLET measurement campaign (Reactive gases, Aerosols and CLouds, Exploring organic matter Transformations) was led in April 2024 at Puy de Dôme Mountain’s observatory (1465 m asl, central France), in the frame of the European research network ACTRIS (Aerosols, Clouds and Trace Gases Research Infrastructure), and supported by the ATMO-ACCESS program. Thanks to its altitude above the surrounding landscape and its geographical localization, this observation site offers unique possibilities of observing a range of atmospheric conditions (free troposphere, boundary layer, clouds) and air masses of different origins and composition (continental, marine, anthropogenic and saharan).A range of real-time instruments were combined for several weeks in order to characterize aerosols at high temporal resolution through their morphological, optical, chemical and physical properties (SMPS, ACSM, OPC…), including the specific monitoring of bioaerosol particles using fluorescence-based intruments (DMT WIBS neo, Swisens Poleno Jupiter). The data were associated with meteorological variables, remote sensing measurements (LIDAR) and backward air mass trajectory analyses (CAT ECMWF ERA5). The main goal was to evaluate the benefits of combining multiple measurements techniques in the characterization of ambient organic aerosols, their interactions with reactive gases and cloud processes, and in the study of the transport and transformations processes of aerosols in dry or wet conditions. During the timeframe of the campaign, several consecutive periods with distinct patterns of aerosol properties could be identified, including distant desert dust intrusions from the Sahara region, elevated concentrations of coarse biological material, and plumes of anthropogenic influence. Detailed description of the different situations will be presented, and the benefits and limits of such multi-instrumented approach in the characterization of aerosols will be discussed. Particular attention has also been paid to the behaviour of fluorescence measurements throughout these events, and on their potential ability to discriminate between biological and non-biological particles.