04 Jul 2022
04 Jul 2022
Status: this preprint is currently under review for the journal AMT.

Sensitivity of aerosol optical depth trends using long term measurements of different sun-photometers

Angelos Karanikolas1,2, Natalia Kouremeti1, Julian Gröbner1, Luca Egli1, and Stelios Kazadzis1 Angelos Karanikolas et al.
  • 1World Radiation Center, Physikalisch-Meteorologisches Observatorium Davos (PMOD/WRC), Davos Dorf, Dorfstrasse 33 7260, Switzerland
  • 2Physics department, ETH Zurich, Zurich, Franscini-Platz 5 8093, Switzerland

Abstract. This work aims to assess differences in the aerosol optical depth (AOD) trend estimations when using high quality AOD measurements from two different instruments with different technical characteristics, operational (e.g. measurement frequency), calibration and processing protocols. The different types of Sun photometers are the CIMEL that is part of AERONET (AErosol RObotic NETwork) and a precision Filter Radiometer (PFR), part of the Global Atmosphere Watch Precision Filter Radiometer network. The analysis operated for two wavelengths (500/501 nm and 870/862 nm for CIMEL/PFR) in Davos, Switzerland, for the period 2007–2019.

For the synchronous AOD measurements, more than 95 % of the CIMEL-PFR AOD differences are within the WMO accepted limits, showing very good measurement agreement and homogeneity in calibration and post correction procedures. AOD trends per decade in AOD for Davos for the 13-year period of analysis were approximately -0.017 and -0.007 per decade for 501 nm and 862 nm (PFR), while the CIMEL-PFR trend differences have been found 0.0005 and 0.0003 respectively. The linear trend difference for 870/862 nm is larger than the linear fit standard error. When calculating monthly AODs using all PFR data (higher instrument frequency) and comparing them with the PFR measurements that are synchronous with CIMEL, the trend differences are smaller than the standard error. The trend differences are also larger than the trend uncertainty attributed to the instrument measurement uncertainty, with the exception of the comparison between the 2 PFR datasets (high and low frequency) at 862 nm. Finally, when calculating time-varying trends, they differ within their uncertainties.

Angelos Karanikolas et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Short Comment on amt-2022-181 - effect of optical airmass', Thomas Eck, 05 Jul 2022
  • RC1: 'Comment on amt-2022-181', Anonymous Referee #1, 15 Jul 2022
  • RC2: 'Comment on amt-2022-181', Anonymous Referee #2, 29 Jul 2022

Angelos Karanikolas et al.

Angelos Karanikolas et al.


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Short summary
The aim of this work is to investigate the limitations of calculating long term trends of a parameter that quantifies the overall effect of atmospheric aerosols on the solar radiation. A main finding is that even instruments with good agreement between their observations can show significantly different linear trends. By calculating time-varying trends the trend agreement improves. We also show that different methods of trend estimation can result to significant trend differences.