In the frame of air quality monitoring the Copernicus Sentinel-5p mission has been designed to identify the concentration of several atmospheric compounds and species in our atmosphere: one of those data is the Ultraviolet Aerosol Indexes (UVAI).
Aerosols are a suspension of fine solid particles or liquid droplets, in air or another gas, and can be natural (fog, dust) or anthropogenic (haze, air pollutants and smoke). The UVAI is a measure of how the aerosols particles interact with ultraviolet radiation [1] and its calculation and distribution gives us an estimation of what kind of aerosols are in the atmosphere. When the UVAI is positive it indicates the presence of absorbing aerosols, like dust and smoke, and is often referred to as the Absorbing Aerosol Index (AAI), whereas it is negative for nonabsorbing aerosols [2][3].
The image above shows a mean distribution of one of the UVAI calculated with Sentinel-5p data (wavelenght pair 354/388 nm) all over the World. The data considered have been acquired from January to February 2019 and filtered according the indication provided into the UV Aerosol Index [L2__AER_AI] Readme. In the maps above the absorbing aerosols are depicted in a yellow-to-black color ramp and the world regions interested are mainly impacted by desert dust (such as the sahara or the arabian peninsula), which emissions vary over the year, burning biomass (depending on the season too) or volcanic ash plumes [4][5]. Non absorbing aerosols (e.g. marine) are usually identified by negative values and we chose an almost flat blue-cyan palette distribution to depict them. The yellow halo coming from the North Africa through the Atlantic Ocean is symptomatic of the dust transportation from the desert, playing an important role as a supplier of nutrient of the Ocean [6][7].
Several interesting patterns can be found browsing and inspecting the UVAI distribution over the months and all over the World thanks to our ESB EO Browser , like the image depicted above showing this strange crown of absorbing aerosols surrounding the Arctic (April 2019 monthly composition) that seems to be cyclic over the seasons. Another case is the high distribution of absorging aerosol over the Bahamas (image below) that appears to be systematic over the months.
Have a look to the ESB EO Browser to browse our monthly maps and understand how atmospheric species and land/marine geophysical entities vary over the seasons and the years! Our collection is increasing systematically and more Sentinel-5p species and Sentinel-3 data are foreseen to be published.
Contains modified Copernicus Sentinel data 2019.
[1] https://projects.knmi.nl/omi/research/product/product_generator.php?info=page&product=aerosol&flavour=AI&long=OMI%20Aerosol%20Index
[2] https://sentinel.esa.int/documents/247904/2476257/Sentinel-5P-TROPOMI-ATBD-UV-Aerosol-Index
[3] http://www.tropomi.eu/data-products/uv-aerosol-index
[4] http://joseba.mpch-mainz.mpg.de/aerosole.htm
[5] https://earth.esa.int/web/sentinel/technical-guides/sentinel-5p/level-2/aerosol-index
[6] https://link.springer.com/chapter/10.1007/978-94-017-3354-0_13
[7] https://www.frontiersin.org/articles/10.3389/fmars.2016.00226/full