Paper Title

Abstract - In this study we analyze the firstnight aerosol optical properties retrieved from the Cimel CE318-T photometer, operating at CLUJ_UBB AERONET station, located on the roof of the building of the Faculty of Environmental Sciences and Engineering, Babeș Bolyai University (BBU) of Cluj-Napoca, Romania, a city with a population of 400 000.The measurement station is part of ACTRIS (Aerosols, Clouds and Trace gases Research Infrastructure, plans to develop a high level infrastructure for the observation and characterization of the atmosphere, by using advanced remote sensing techniques complemented by in-situ methods, in order to fulfil 2 national facility criteria for integration within ACTRIS. UBB will develop an international level atmospheric observatory that will host the ACTRIS-RI national facilities for aerosol and cloud remote sensing) by acquiring specific equipment and R&D software. The Cimel sun-sky-lunar photometer was acquired through this project. The Cluj-Napoca AERONET measurement station can be considered representative for the whole Transylvanian territory, and also for the Pannonian Basin, given the limited coverage in Hungary, Austria, and South-Western Ukraine.The photometer night measurements were started in September 2022. We analyzed the trends of optical properties such as AOD at 440 nm and 440-870 Ångström exponent and compared the findings with the day time measurements in order to assess any diurnal variability. Keywords - AERONET, aerosol, lunar photometer, Aerosol optical depth, Ångström exponent Acknowledgement: This work was supported by the project entitled “Strengthening the participation of the ACTRIS-RO consortium in the pan-European research infrastructure ACTRIS” SMIS CODE 107596, co-financed by the European Union through the Competitiveness Operational Programme 2014–2020.