Raman LIDAR-Based Aerosol Profiling for Atmospheric Studies in Ultra High Energy Cosmic Ray Observatories

The presence of aerosols in the atmosphere impacts various aspects, underscoring the importance of continuous monitoring of these minute particles. Within ultra-high-energy cosmic ray observatories, neglecting the attenuation of light due to atmospheric molecules and aerosols introduces a significant systematic error in determining the properties of the primary particle. At the Pierre Auger Observatory, a comprehensive atmospheric monitoring program has been developed to correct observations of extensive atmospheric showers conducted with the Fluorescence Detector (FD). This work describes the Raman lidar of the Pierre Auger Observatory, operational since September 2013, which allows monitoring of aerosols above the central laser facility. The vertical profiles of aerosol optical depth have been obtained for the period 2013-2022, highlighting a seasonal variability and obtaining, for those nights with a low aerosol load, an average value of 0.04 at a reference altitude of 4.5 km above ground level. The vertical distribution of aerosols can be modeled using two or three parameters, with lidar data better described by the three-parameter model. Information obtained from Raman lidar measurements is also used within the collaboration as a cross-check with other methods used to determine aerosol attenuation. Next, the development of a Raman lidar system, both hardware and software components, for monitoring atmospheric aerosols is described. Given the regions where cosmic ray observatories are located, solutions have been tested to simplify maintenance, eliminating the need for specialized personnel on-site. This objective is achieved by using a bundle of optical fibers within the receiver. The initial observations conducted in L’Aquila are reported, which have proven to be very encouraging.