Retrieval of Aerosol Properties from Direct Solar Irradiance Data with High Temporal and Spectral Resolution Using GRASP

Several sun photometer networks (e.g. the Aerosol Robotic Network (AERONET), the Global Atmospheric Watch-Precision Filter Radiometer (GAW-PFR) retrieve aerosol optical depth (AOD). AERONET provides more aerosol properties such as the effective radius and the single scattering albedo through inversion modelling using sky radiance measurements. However, the data availability for such properties is limited due to the low number of sky radiance scans and cloudiness. In contrast, AOD measurements are significantly more frequent (every minute for GAW-PFR). In the past, methods were developed to retrieve aerosol properties using only direct sun scans. Kazadzis et al., 2014 used linear estimation technique to retrieve the effective radius and volume concentration using only AOD measurements. The Generalized Retrieval of Aerosol and Surface Properties (GRASP) uses multi-term least square method to retrieve the AOD, the volume concentration, the median radius and geometric standard deviation separately for fine and coarse mode. Previous studies concern the application of GRASP-AOD to CIMEL sun photometers Torres Fuertes, 2021. In this study, we aim to apply it to GAW-PFR instruments (PFRs) at common locations with AERONET, assess the retrieval homogeneity with AERONET products and investigate the effect of the wavelength differences and AOD uncertainties. Also, we aim to apply the method to the Precision Spectroradiometers (PSR) and investigate the potential improvements using higher spectral range and resolution. Preliminary retrievals in a common GAW-PFR and ARONET station Hohenpeissenberg) show good results for the fine and coarse mode AOD separation and the fine mode median radius (correlation factor with AERONET standard inversions >0.9 for AOD and >0.8 for fine mode radius). For the coarse mode the retrievals are less accurate, mainly for the median radius in which GRASP-AOD shows low sensitivity to its fluctuations.ReferencesKazadzis, S., Veselovskii, I., Amiridis, V., Grbner, J., Suvorina, A., Nyeki, S., Gerasopoulos, E., Kouremeti, N., Taylor, M., Tsekeri, A., and Wehrli, C. (2014): Aerosol microphysical retrievals from precision filter radiometer direct solar radiation measurements and comparison with AERONET, Atmos. Meas. Tech., 7, 20132025, https://doi.org/10.5194/amt-7-2013-2014.Torres, B. and Fuertes, D. (2021): Characterization of aerosol size properties from measurements of spectral optical depth: a global validation of the GRASP-AOD code using long-term AERONET data, Atmos. Meas. Tech., 14, 44714506, https://doi.org/10.5194/amt-14-4471-2021.