05: Ground-based solar radiation measurements and the study of atmospheric aerosols

Original abstract title: Aerosol optical depth ground-based measurement and measurement-modelling advancements

Angelos Karanikolas1,2
Supervisors: Louise Harra1,2, Stelios Kazadzis 1
Group Leader: Julian Groebner1
Collaborating team members: Natalia Kouremeti1, Luca Egli1
External collaborators: Masahiro Momoi3, Benjamin Torres4, Monica Campanelli5, Victor Estellés6,5, Gaurav Kumar6, Lionel Doppler7, Marcos Herreras Giralda3, Panagiotis Ioannis Raptis8,9, Fountoulakis Ilias10, Dimitra Kouklaki8,9 and Kyriaki Papachristopoulou8

  1. Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC), Davos Dorf, Switzerland
  2. Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
  3. GRASP-SAS, Lille, France
  4. Laboratoire d’Optique Atmosphérique (LOA), University of Lille, Lille, France
  5. Institute of Atmospheric Sciences and Climate, ISAC-CNR, Rome, Italy
  6. Earth Physics and Thermodynamics Department, University of Valencia, Valencia, Spain
  7. Deutscher Wetterdienst (DWD), Meteorologisches Observatorium Lindenberg (MOL-RAO), Lindenberg (Tauche), Germany
  8. National Observatory of Athens, Athens, Greece
  9. Kapodistrian University of Athens, Athens, Greece
  10. National Academy of Athens, Athens, Greece

Aerosols are an important constituent in the study of atmosphere. They affect the Earth’s energy budget by interacting with radiation, affecting also the solar radiation exposure at the surface [Wild 2012]. They also play a crucial role in cloud formation and properties [Fan et al. 2016].  Interactions between aerosols and clouds are important for radiative forcing attribution, climate modelling and weather forecasts [Rosenfeld et al. 2014, Glotfelty et al. 2019]. Finally, aerosols are one of the most important air pollutants [WHO 2013].

Aerosols are a heterogeneous mixture of non-gaseous particles. To study their effects on climate we need to quantify several properties of the aerosol column. One way to achieve this is the use of solar radiation measurements from ground-based instruments (which can also serve as reference for satellite instruments).

One of the most important parameters regarding aerosols is the Aerosol Optical Depth (AOD), which describes the aerosol column effect on solar radiation extinction [WMO 2003]. The AOD is observed through Sun photometers. Sun photometers are instruments that measure the direct solar irradiance reaching the ground at specific wavelengths. To retrieve the AOD through the solar irradiance, we require the solar irradiance at the top of the Earth’s atmosphere (calibration constant) and the effect of gases. Several networks of different Sun photometers are used worldwide to measure the AOD.

There are other properties defining the optical and microphysical properties of aerosols like the single scattering albedo (SSA), the effective radius (Reff), the total volume concentration (Cv). SSA shows the balance between radiation absorption and scattering from aerosols, Reff is the weighted average of their radius, Cv their volume per atmospheric air unit. These properties can be retrieved using different components of the solar radiation, the AOD and additional information like the gas absorption.

This thesis aims to contribute to the assessment of the differences between different instruments and methodologies for aerosol properties’ retrievals, the homogenisation of sun photometric networks and the improvement of the aerosol monitoring. It includes four objectives:

  • The first objective was about the consistency between the AOD and its long-term trends between two different co-located sun photometers in Davos during 2007-2019 (one belonging to the Global Atmospheric Watch-Precision Filter Radiometer or GAW-PFR network and another to AErosol RObotic NETwork or AERONET). The study includes the effect of factors such as the trend analysis method and the temporal resolution [Karanikolas et al. 2022]. Most differences were within the corresponding uncertainties.

  • The second objective was an assessment of the differences between the networks GAW-PFR and SKYNET and the effect of the different calibration methods that the two networks are using. The GAW-PFR network uses the Langley Plot method (LP) in high altitude locations [Kazadzis et al. 2018]. The SKYNET instruments (Prede POM sky radiometers) are calibrated ‘on site’ with the Improved Langley Plot method (ILP) [Nakajima et al. 2020]. For the investigation we used measurements from co-located instruments in Davos and Rome during campaigns of 2017-2021 [Karanikolas et al. 2024]. The results showed a systematic lower POM AOD, which can be attributed to modelling required for the ILP calibration method.

  • The third objective is about the retrieval of aerosol size properties and concentration using only AOD observations through an aerosol model called GRASP [Torres et al. 2017]. Preliminary results suggest higher accuracy at small aerosols (fine mode) and concentration retrievals.

  • The fourth objective aims to the retrieval of spectral SSA. This is accomplished using the Precision Spectroradiometer, which can measure the global and direct solar irradiance simultaneously at 1024 wavelengths between 300 and 1020 nm.

Aerosols remain one of the most important sources of uncertainties in climate science [IPCC 2021] and weather forecasting [Huang & Ding 2021]. An improved aerosol monitoring can be beneficial to the study of major global issues like climate change and air pollution.

References

Fan, J., Wang, Y., Rosenfeld, D., and Liu, X.: Review of Aerosol–Cloud Interactions: Mechanisms, Significance, and Challenges, J. Atmos. Sci., 73, 4221–4252, https://doi.org/10.1175/jas-d-16-0037.1, 2016. 

Glotfelty, T., Alapaty, K., He, J., Hawbecker, P., Song, X., and Zhang, G.: The Weather Research and Forecasting Model with Aerosol-Cloud Interactions (WRF-ACI): Development, Evaluation, and Initial Application, Mon. Weather Rev., 147, 1491–1511, https://doi.org/10.1175/MWR-D-18-0267.1, 2019. 

Huang, X. and Ding, A.: Aerosol as a critical factor causing forecast biases of air temperature in global numerical weather prediction models, Sci. Bull., 66, 1917–1924, https://doi.org/10.1016/j.scib.2021.05.009, 2021.

Karanikolas, A., Kouremeti, N., Gröbner, J., Egli, L., and Kazadzis, S.: Sensitivity of aerosol optical depth trends using long-term measurements of different sun photometers, Atmos. Meas. Tech., 15, 5667–5680, https://doi.org/10.5194/amt-15-5667-2022, 2022.

Karanikolas, A., Kouremeti, N., Campanelli, M., Estellés, V., Momoi, M., Kumar, G., and Kazadzis, S.: Intercomparison of AOD retrievals from GAW-PFR and SKYNET sun photometer networks and the effect of calibration, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2024-84, in review, 2024.

Kazadzis, S., Kouremeti, N., Nyeki, S., Gröbner, J., and Wehrli, C.: The World Optical Depth Research and Calibration Center (WORCC) quality assurance and quality control of GAW-PFR AOD measurements, Geosci. Instrum. Method. Data Syst., 7, 39–53, https://doi.org/10.5194/gi-7-39-2018, 2018. 

IPCC: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M. I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J. B. R., Maycock, T. K., Waterfield, T., Yelekçi, O., Yu, R., and Zhou, B., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2391 pp. https://doi.org/10.1017/9781009157896, 2021. 

Nakajima, T., Campanelli, M., Che, H., Estellés, V., Irie, H., Kim, S.-W., Kim, J., Liu, D., Nishizawa, T., Pandithurai, G., Soni, V. K., Thana, B., Tugjsurn, N.-U., Aoki, K., Go, S.,

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