Investigating Total Aerosol Load of Eastern Mediterranean Basin With Sentinel-5P

Abstract

The Eastern Mediterranean Basin has a high aerosol load formed from different sources and is subject to atmospheric transport. This region, which includes the deserts of Africa and the Middle East, is one of the regions that is most affected by climate change. Aerosols, which are highly present in the Eastern Mediterranean Basin in a form of dust, directly affect the radiative balance of the earth by absorbing and/or scattering the sun rays reaching the atmosphere and indirectly affect the balance by affecting cloud formation by acting as a nucleus. This study aims to investigate the spatial and temporal distribution of aerosols over the Eastern Mediterranean Basin with the daily Absorbing Aerosol Index (AAI) data obtained from the Sentinel-5P satellite, which carries a spectrometer called TROPOMI in order to quantify specific pollutants over the atmosphere. Sentinel-5P is a Low-Earth orbiting satellite that performs atmospheric measurements with high spatiotemporal resolution (5.5 km x 3.5 km). While retrieving the data, The Level-2 Reprocessing UVAI product, which is the aerosol index measured between the wavelength ranges of 340/380, 354/388, and 335/367 nm, was converted to the Level-3 AAI product by quality standards, that represents aerosols that absorb the incoming solar rays. After retrieving the data, NaN values, which are present due to the orbit's geometry, were removed from the dataset. Then, daily data were visualized by days, months, years, and seasons and the distribution of aerosol load was examined. Time series graphs were created with Mann Kendall trend test, and then the data were decomposed in order to visualize the trends that AAI product includes. As a result of these analyses, it was seen that the Level-3 AAI data were consistent with the meteorological seasons. Except for the cases where NaN is rarely observed due to the geometry of the satellite, and the extreme cases caused by the effect of some dust oscillations, the temporal and spatial changes of the aerosols can be examined in an accurate way with the Sentinel-5P data. It was seen that the AAI value in the Eastern Mediterranean Basin shows a decreasing trend over the four years. In Türkiye, there were no significant trends over the four years. However, when the data is divided into years, for example, an increase trend was observed in 2019 and a decreasing trend was observed in 2020. As North Africa and the Northern Arabian Peninsula are constantly exposed to dust storms, no significant trend has been observed in these two regions. Additionally, three dust related cases have been investigated, one of which is the forest fires that happened over Türkiye in the summer months of 2021. During the case study analyses, the Sentinel-5P data visuals have been compared with satellite images, such as MODIS and EUMETSAT. The ground-based measurements for temperature, wind speed, and atmospheric pressure have been used to find the causes and drivers of the dust episodes. PM10 measurements were obtained from the Continuous Monitoring Center, a ground-based measurement network, and high PM10 concentrations have been observed during dust events. As a result of these comparisons, the compatibility of the AAI data of the Sentinel-5P satellite with other satellites has been observed.