Detection of bioparticles by synergy of depolarisation-LIF lidars supported by in situ measurements at the high alpine station of Helmos, Greece, during the CHOPIN campaign 2024

The Cleancloud Helmos OrograPhic site experimeNt (CHOPIN) campaign took place in autumn 2024 at a unique high-altitude location at Mount Helmos, Greece (38.0^oN, 22.2^oE) ideal for targeted studies of aerosol-cloud interactions (ACI) due to its strategic location, serving as a crossroad for different aerosol transport paths. This unique position allows the detection of a wide range of particles like wildfire smoke, continental polluted, marine and mineral dust from Sahara, as well as bioparticles (pollen, bacteria, fungal spores) from near- and long-range sources. State-of-the-art laser remote sensing and in situ instrumentation was implemented at Mount Helmos at two level heights: 1700 m (remote sensing instrumentation) and 2314 m a.s.l. (in situ instrumentation) to characterize the incoming air masses in terms of their bioparticle content and study the role of bioparticles in cloud formation. In this study we will focus on data obtained by two lidar systems: the two-wavelength (532 -parallel and cross depolarization and 1064 nm) depolarization aerosol lidar system (AIAS), and the NTUA/EPFL/FORTH 4-wavelength elastic-Raman-laser induced fluorescence (LIF) lidar system (ATLAS-NEF) to provide vertical profiles of aerosol optical properties (extinction and backscatter coefficients and lidar ratio at 355 nm, backscatter Ångström exponents at 355/532nm, 532/1064 nm, particle depolarisation lidar ratio at 532 nm), water vapor mixing ratio, fluorescence capacity and fluorescence backscatter coefficients at 470 nm. We present cases of Saharan dust intrusions with increased values of the aerosol backscatter coefficient and high particle depolarization ratios (δ₅₃₂ ~0.20-0.25) and increased values of lidar ratios (LR~40-55 sr), high numbers of ice-nucleation particles (INPs) obtained with a PINE instrument and strong signals obtained at the 3 channels of the Wideband Integrated Bioparticles Sensor (WIBS) operating at the (HAC)² station indicate the presence of bioparticles able to enhance cloud formation.