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 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.

Iron content in aerosol particles and its impact on atmospheric chemistry

“…1B shows the image captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite leaving Africa and extending all the way to the Caribbean on August 14, 2023. 11 Similar events were reported for Greece, 12 the western United States, 13 East Asia, 14,15 and the subtropical West Pacific region impacting air quality, radiative forcing, and the UV index at ground levels. 16 These dust events are the main source of micronutrients such as Fe to the oceanic biota, which require Fe species to be bioaccessible.…”

The ASPIRE Project: Atmospheric Parameters Affecting Solar Irradiance and Solar Energy in Athens, Greece—Overview and Results

“…The available GHI was less affected relative to other radiometric quantities, but its reduction can be significant for solar energy production systems, such as PVs. In view of the GHI reduction of up to 17% in the GAA during August 2021 [3], we have estimated the efficiency of different PV materials based on spectral solar irradiance measurements for different aerosol conditions. More specifically, we have analyzed measurements from two days: an aerosol-free day (16 August) and a day with very high aerosol load from smoke (18 August).…”

“…The optimum absorption of the two technologies under study, gallium arsenide (GaAs) and cadmium telluride (CdTe), is mainly observed in the visible area of the spectrum. GaAs is sensitive to a wider spectral area, while both Recent findings, based on ASPIRE campaign data, showed that smoke and dust aerosols during August 2021 led to reductions in UVI in Athens by up to 53%, in vitamin D dose by up to 50%, in PAR up to 21% and in GHI up to 17%, with potential implications for health, agriculture and energy [3]. The above results indicate that solar radiation biological doses, e.g., UV index, vitamin D and PAR, can be significantly affected by high-aerosol loads in sun-rich countries like Greece even in the summer months.…”

“…The spectral responses, SR (A W −1 ), of the two aforementioned technologies (GaAs and CdTe) were considered in order to observe their performance under aerosol-free (e.g. 16 August 2021) and high-AOD conditions (e.g., 18 August 2021) when the air quality ove the city of Athens was burdened by wildfires that occurred in the surrounding areas [3] Their performance was calculated using Equation ( 1) and is illustrated in Figure 3. The relative difference between the two technologies for the two cases was calculated using Equation ( 2 In the case of low AOD (16 August), the difference between the performance of the under-study technologies remains stable during the day, at approximately 27%, whereas the presence of smoke in the atmosphere (18 August) decreases both technologies performance.…”

The extreme heat wave of late July/early August 2021 in Greece under the context of the direct effect of anthropogenic greenhouse gases

“…As a result, over 2300 excess deaths-excluding those related to the COVID-19 pandemic-compared to the 2016-2020 average were recorded during the episode, based on Eurostat data (Politico, 2021). Furthermore, the extreme heat contributed to the outbreak of five major wildfires in the south and central Greece, which collectively burnt $94,000 ha (Giannaros et al, 2022) and resulted in significant deterioration of air quality due to smoke (Masoom et al, 2023).…”