In August 2021, a historic heatwave was recorded in Greece which resulted in extreme wildfire events
that strongly affected the air quality over the city of Athens. Saharan dust was also transferred over Greece on
certain days of the same period due to the prevailing southern winds. The impact of these events on air quality
and surface solar radiation is investigated in this study. Event characterization based on active and passive remote
sensing instrumentation has been performed. The study shows that significantly increased levels of air pollution
were recorded from the end of July to the first week of August. The smoke led to unusually high aerosol optical depth (AOD) values (up to 3.6 at 500 nm), high Ångström exponent (AE) (up to 2.4 at 440–870 nm), and a strong
and negative dependence of single-scattering albedo (SSA) on wavelength that was observed to decrease from
0.93 at 440 nm to 0.86 at 1020 nm, while the dust event led to high AOD (up to 0.7 at 500 nm), low AE (up to
0.9 at 440–870 nm), and a positive dependence of SSA on wavelength that was observed to increase from 0.89
at 440 nm to 0.95 at 1020. Furthermore, the smoke plume was also detected over the PANhellenic GEophysical
observatory of Antikythera on 7 August, which is about 240 km away from Athens. Increased AOD values (up
to 0.90 at 500 nm) associated with a high fine-mode AOD (up to 0.85 at 500 nm) and decrease in SSA
with wavelength suggested the dominance of fine biomass burning aerosols. The impact of dust and smoke on
solar irradiance revealed significant differences in the spectral dependence of the attenuation caused by the two
different aerosol types. The attenuation of solar irradiance in the ultraviolet (UV-B) spectrum was found to be
much lower in the case of dust compared to smoke for similar AOD500 values. Differences were less pronounced
in the near-infrared and visible spectral regions. The large AODs during the wildfires resulted in a decrease in the
noon UV index by up to 53 %, as well as in the daily effective doses for the production of vitamin D (up to 50 %), in the daily photosynthetically active radiation (up to 21 %) and in the daily global horizontal irradiance (up to 17 %), with serious implications for health, agriculture, and energy. This study highlights the wider impacts of
wildfires that are part of the wider problem for Mediterranean countries, whose frequency is predicted to increase
in view of the projected increasing occurrence of summer heatwaves.