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This paper presents the new photometer CE318-T, able to perform daytime andnight-time photometric measurements using the sun and the moon as lightsource. Therefore, this new device permits a complete cycle ofdiurnal aerosol and water vapour measurements valuable to enhance atmosphericmonitoring to be extracted. In this study we have found significantly higherprecision of triplets when comparing the CE318-T master instrument and the Cimel AErosol ROboticNETwork (AERONET) master (CE318-AERONET) triplets as a result of the newCE318-T tracking system. Regarding the instrument calibration, two newmethodologies to transfer the calibration from a reference instrument usingonly daytime measurements (Sun Ratio and Sun-Moon gain factor techniques)are presented and discussed. These methods allow the reduction of the previous complexitiesinherent to nocturnal calibration. A quantitative estimation of CE318-T AODuncertainty by means of error propagation theory during daytime revealed AODuncertainties (uDAOD) for Langley-calibrated instruments similar to theexpected values for other reference instruments (0.002–0.009). We have alsofound uDAOD values similar to the values reported in sun photometry forfield instruments ( ∼  0.015). In the case of the night-time period, theCE318-T-estimated standard combined uncertainty (uNAOD) is dependent not only on thecalibration technique but also on illumination conditions and theinstrumental noise. These values range from 0.011–0.018 for Lunar Langley-calibrated instruments to 0.012–0.021 for instruments calibrated using theSun Ratio technique. In the case of moon-calibrated instruments using the Sun-Moon gain factor method and sun-calibrated usingthe Langley technique, we found uNAOD ranging from 0.016 to 0.017 (up to 0.019 in 440 nm channel), not dependent onany lunar irradiance model.A subsequent performance evaluation including CE318-T and collocatedmeasurements from independent reference instruments has served to assess theCE318-T performance as well as to confirm its estimated uncertainty. DaytimeAOD evaluation, performed at Izaña station from March to June 2014,encompassed measurements from a reference CE318-T, a CE318-AERONET master instrument, aPrecision Filter Radiometer (PFR) and a Precision Spectroradiometer (PSR)prototype, reporting low AOD discrepancies between the four instruments (upto 0.006). The nocturnal AOD evaluation was performed using CE318-T- andstar-photometer-collocated measurements and also by means of a day/night coherencetransition test using the CE318-T master instrument and the CE318 daytime data from theCE318-AERONET master instrument. Results showed low discrepancies with the star photometerat 870 and 500 nm channels ( ≤  0.013) and differences with AERONETdaytime data (1 h after and before sunset and sunrise) in agreement with theestimated uNAOD values at all illumination conditions in the case ofchannels within the visible spectral range, and only for high moon'sillumination conditions in the case of near-infrared channels.Precipitable water vapour (PWV) validation showed a good agreement betweenCE318-T and Global Navigation Satellite System (GNSS) PWV values for allillumination conditions, within the expected precision for sun photometry.Finally, two case studies have been included to highlight the ability of thenew CE318-T to capture the diurnal cycle of aerosols and water vapour as wellas short-term atmospheric variations, critical for climate studies

The new sun-sky-lunar Cimel CE318-T multiband photometer – a comprehensive performance evaluation