Investigation of the effects of the Greek extreme wildfires of August 2021 on air quality and spectral solar irradiance

Abstract

Abstract. 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 in the same period due to the prevailing southern winds. The impact of these events on air quality and surface solar radiation are 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 during the end of July/first week of August. The smoke led to unusually high AOD values (up to 3.6), high Ångström Exponent (AE) (up to 2.4) 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 signifying the presence of strong absorbing aerosols. While, the dust event led to high AOD (up to 1.4), low AE (up to 0.9) and positive dependence of SSA on wavelength that was observed to increase from 0.89 at 440 nm to 0.95 at 1020 nm indicating large forward scattering due to coarse particles. Furthermore, the analysis of the smoke aerosol optical properties during the transfer from the source to a distance of about 240 km revealed that the SSA and AE changed significantly during the transfer, which lasted approximately 9 h. The transport of the plume led to an impressive change in the spectral shape of SSA whose value significantly increased pointing to the aging of smoke and the dilution of plumes while the transport. The impact of dust and smoke on spectral solar irradiance reveals significant differences in the spectral shape of attenuation caused by the two different aerosol species. The attenuation of solar irradiance in UV-B irradiance was found to be least in case of dust and highest due to smoke (up to 60 % or more) and intermediate in the case of a mixture of smoke and dust. The attenuation was comparatively less in NIR region (mostly within 20 % but it even reached up to 40 % in the presence of smoke) and VIS region (but greater than NIR region). Also, the AOD variations from climatology led to decrease in UV Index up to 53 %, in vitamin-D up to 50 %, in photosynthetically active radiation up to 21 % and in GHI up to 17 %, with implications on health, agriculture and energy. This study highlights the wider impacts of wildfires that are part of the wider problem of the Mediterranean countries, whose frequency is predicted to increase in view of the projected increasing occurrence of summer heatwaves.

Correlation between Two Sunshine Parameters and Three Hydrometeorological Parameters

“…It should be noted that the correlation in this study was in a normal condition. In unnormal conditions, such as in the Greek extreme wildfires of August 2021, the UV index at noon decreased by up to 53 % [26]. In this case, their relationship might be shifted.…”

Aerosol Optical Properties and Type Retrieval via Machine Learning and an All-Sky Imager

“…For instance, dust episodes from the Sahara Desert are a common natural occurrence, accounting for ~23% of the annually averaged AOD [65]. Other sources are sea-salt aerosols emitted by the surrounding sea bodies [66], biomass burning [67], wildfires [68,69], and photochemical pollution [70,71]. Raptis et al [72] performed a detailed analysis using decadal measurements of aerosol properties (AOD 440 nm and AE 440-870 nm ) from the NOA AERONET station to extract the seasonality and the trends of aerosols in the region.…”

Evaluation of the Solar Energy Nowcasting System (SENSE) during a 12-Months Intensive Measurement Campaign in Athens, Greece

“…Ιn the histogram in Figure 7, we show the absolute difference between the climatological PWV used in the model and the measured from AERONET It should also be highlighted that for cases of extreme or unpredictable aerosol events, the AOD differences might be a lot higher, thus their propagation to estimated irradiance could be much more significant. During the ASPIRE campaign, there were some days with extreme wildfires in Greece, that were studied by Masoom et al [44], when the decrease of GHI due to smoke was in the range of 10-20%. Another study [45] found that during in a very intense and rare dust event over Athens, the GHI decrease was 40-50% and DNI 80-90%.…”