Measurements

AIR QUALITY MEASUREMENTS

a. Long-term measurements of the ozone layer and the optical depth of suspended particles in Athens

Figure 9 presents the daily values of the total ozone column in Athens in the period 2003-2019, as measured by the Brewer type spectrophotometer which is installed on the roof of BRFAA. As seen on Figure 9, there is a very good agreement between the ground measurements of BRFAA and the satellite observations from TOMS and OMI (correlation coefficients greater than +0.9). Accordingly, large correlations are also found with the measurements of the European satellites, MetOpA and MetOpB. The ozone layer appears to be stabilised over Attica, with no significant change during the past 18 years or so. The average value of the ozone layer remains steady at 320 Dobson units, a quantity corresponding to a layer thickness of 3.2 mm. Respectively, the levels of the inhabitants’ exposure to ultraviolet solar radiation remain constant, as confirmed by the satellite observations of the erythemal dose of solar radiation over the Athens basin. The results were presented in a recent scientific paper by Eleftheratos et al. (2021).

Figure 9. Daily values of the ozone layer in Athens from the ground measurements in the Academy of Athens and the observations of the satellite instruments, OMI, TOMS, GOME-2A and GOME-2B (Eleftheratos et al., 2021).

The measurements of the Brewer spectrophotometer were used to study the temporal changes of the aerosol optical depth (AOD) in Athens for the period of 2008-2014. The results are presented in Figure 10. The Brewer measurements showed a downward trend of AOD at 437 nm during the period under study, as well as a very good agreement with the corresponding measurements from the CIMEL photometer of the international AERONET network of NASA. The results were presented in the scientific paper by Diémoz et al. (2016).

Figure 10. Temporal changes of the aerosol optical depth in Athens during the period of 2008-2014 from the measurements of the Brewer spectrophotometer at 437 nm. On the right, the Brewer measurements are presented in comparison to the corresponding measurements of the CIMEL photometer (Diémoz et al., 2016).

b. Measurements of sulfur dioxide, solar radiation and aerosol optical depth in Athens during forest fires

Figure 11 presents the measurements of the total column of sulfur dioxide (SO2) in Athens during the forest fire of August 2009 that hit areas in Northeast Attica, from Grammatiko and Marathon to Pikermi and Pallene, burning part of Penteli in its passage. The concentrations of the total SO2 column, as measured at BRFAA on August 22 and 23, were approximately 3 times higher than the normal values. On Figure 11, the diagram on the left shows the smoke that passed over BRFAA on August 22, 2009; the diagram on the right shows the measurements of SO2 from the spectrophotometer.

Figure 11. On the right, measurements of the total column of sulfur dioxide (SO2) at the BRFAA during the forest fire in Northeast Attica in August, 2009. On the left, the cloud of suspended particles from the forest fire, which engulfed Attica.

The measurements of erythemal solar radiation during the days of the forest fires (August 22-23) were compared to the measurements before the fires (August 19) as shown in Figure 12. On August 23, the smoke remained over the station for the entire day, which resulted in the decrease of erythemal radiation from 160 to 40 mW/m2. The comparison of the UV-MFR measurements at two wavelengths (311 nm και 368 nm) showed that the decreases of radiation at UV-B (311 nm) were greater than the radiation decreases at UV-A (368 nm). This is due to the increased scattering of aerosols at shorter wavelengths. The decreases were even up to 95% and 80%, for UV-B and UV-A solar radiation, respectively. The results were presented in the scientific paper by Amiridis et al. (2012).

Figure 12. (a) Measurements of erythemal radiation from the BRFAA Brewer spectrophotometer before and during the forest fires of August 2009 in Attica. (b) Measurements at two characteristic wavelengths (311 nm και 368 nm) from the UV-MFR photometer (Amiridis et al., 2012).

Figure 13 presents the measurements of SO2 during the recent catastrophic fires of August 2021. The concentrations of the total SO2 column that were measured at BRFAA during the first 11 days of August (period of forest fires) and on August 18-19 (forest fires in Lavreotiki and Vilia, Attica) were up to 8 times higher than the average value of SO2 in August. The average value is from the days without forest fires. The photos on the upper part of Figure 13 were taken at the BRFAA station on August 5, 2021 and they show the wildfire smoke in the morning and at sunset. The diagrams at the bottom of Figure 13 illustrate the daily measurements of SO2 and the average daily values of the optical depth of suspended particles at 320.1 nm from the Brewer spectrophotometer measurements in August 2021.

Figure 13. Measurements of the total column of sulfur dioxide (SO2) and of the optical depth of aerosols at 320.1 nm at BRFAA in August 2021.

c. Detection of transnational transport of sulfur dioxide of volcanic origin

The SO2 measurements of BRFAA were included in an international study for the detection of SO2 of volcanic origin from the existing network of Brewer spectrophotometers. Comparisons with independent ground and satellite measurements, as well as theoretical model calculations, confirmed the Brewer network’s ability to detect volcanic concentrations of SO2. The comparison with OMI and GOME-2 satellite retrievals showed a statistically significant agreement between the Brewer network data and the collocated satellite overpasses in the case of the eruption of Kasatochi Volcano in Alaska in August 2008 (see Figure 14). The simulations of the total SO2 column from the MACC project (Monitoring of atmospheric composition and climate) showed that the large increases of SO2 in Europe following the eruption of Bárðarbunga Volcano in Iceland in September 2014 were not caused by local pollution sources or ship emissions, but were clearly linked to the volcanic eruption. The increase of SO2 at ground level and in the troposphere of Europe was identified by other ground networks as well (Air-Base and EARLINET). It was suggested that the combination of the measurements of the existing Brewers network with other ground and satellite networks could create a useful tool to forecast high SO2 values both at ground level and in air flight corridors following future eruptions. The results were presented in the scientific paper by Zerefos et al. (2017).

Figure 14. Detection of SO2 of volcanic origin in August 2008 following the eruption of Kasatochi volcano in Alaska (Zerefos et al., 2017).

d. Measurements of ozone and carbon monoxide at the Ν.Ε.Ο.

The researchers of CEEH of BRFAA analysed the atmospheric concentrations of ozone (Ο3) and carbon monoxide (CO) in Messinia, from the measurements of the N.E.O. station which has been operating in Methoni since 2016. The station is part of the PANACEA national research infrastructure and its aim is to monitor on a long-term basis the concentrations of basic suspended particles and air pollutants in order to understand the factors determining the levels and variability of pollution in remote areas. The measurements of air pollutants were compared to the corresponding measurements of Finokalia station in Crete. The correlation coefficient between the daily values of Ο3 in Methoni and Finokalia is approximately +0.6. A similar correlation was also found for CO (Figure 15). The scientific results were presented at the 2nd scientific conference of PANACEA, which was held online between September 29 and October 1, 2020.

Figure 15. Daily measurements of O3 (left) and CO (right) in Methoni, N.E.O., and Finokalia, Crete.

e. Educational activities at the N.E.O.

The 3rd educational Workshop of the AdaptNET project on the impact of climate change on agriculture was held at the Costa Navarino, Messinia from February 3 to February 8, 2020. The AdaptNET project (Strengthening education, research and innovation for climate smart crops in India) is an ERASMUS+ CAPACITY BUILDING project funded by the European Commission. The Workshop was attended by 29 Indian teachers/scientists as well as 15 postgraduate students from Greece. The training was organized by Dr. Ioannis Kapsomenakis and Dr. Dimitris Voloudakis.