Abstract
The gap in knowledge regarding the radiative effects of aerosols in the UV region of the solar spectrum is large, mainly due to the lack of systematic measurements of the aerosol single scattering albedo (SSA) and absorption optical depth (AAOD). In the present study, spectral UV measurements performed in Thessaloniki, Greece by a double monochromator Brewer spectrophotometer in the period 1998–2017 are used for the calculation of the aforementioned optical properties. The main uncertainty factors have been described and there is an effort to quantify the overall uncertainties in SSA and AAOD. Analysis of the results suggests that the absorption by aerosols is much stronger in the UV relative to the visible. SSA follows a clear annual pattern ranging from ~0.7 in winter to ~0.85 in summer at wavelengths 320–360 nm, while AAOD peaks in summer and winter. The average AAOD for 2009–2011 is ~50% above the 2003–2006 average, possibly due to increased emissions of absorbing aerosols related to the economic crisis and the metro-railway construction works in the city center.
Highlights
Atmospheric aerosols can be of natural or anthropogenic origin and their impact on human health is well established [1,2,3]
It is based on the calculation of ratios between nearly simultaneous ground based measurements of direct and global UV irradiance at 5 different wavelengths, which are compared with the corresponding ratios simulated by a radiative transfer model (RTM) for the particular solar zenith angle (SZA) but for different single scattering albedo (SSA) values
Considering that CIMEL is a well-calibrated instrument, developed for aerosol optical depth (AOD) measurements, and that the agreement between AOD from Brewer#086 and CIMEL is within the uncertainties of the later, the results presented in Figure 1 provide a very strong indication that the quality of the SSA and AAOD from Brewer#086 has been optimized after re-evaluating the direct and global UV datasets
Summary
Atmospheric aerosols can be of natural or anthropogenic origin and their impact on human health is well established [1,2,3]. The absorption efficiency of an aerosol layer is usually quantified either using the mean columnar single scattering albedo of the layer (in many studies called single scattering albedo, and on is referred as SSA) or the absorption optical depth (AAOD) Particular aerosol types, such as sulfate, mainly scatter solar radiation in the ultraviolet (UV) and visible (VIS) wavelengths, while other, such as organic aerosols, absorb a larger fraction of solar radiation [16,17]. In the last twenty years, large global networks of sun photometers have been established, providing systematic measurements of the SSA and the AAOD in the visible and near infrared (NIR) regions of the solar spectrum [28,29], which in turn have been exploited for the improved description of the radiative effects of aerosols in radiative transfer models [30,31]. The procedures which ensure the quality of the data are analytically described, while there has been an effort to quantify the sensitivity of the used algorithm on different parameters and the relative overall uncertainty budget
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