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Absorbing Aerosol Index (AAI)   indicates the presence of elevated absorbing aerosols in the troposphere like desert dust, smoke, and volcanic ash. AAI separates the spectral contrast at two ultraviolet (UV) wavelengths caused by absorbing aerosols from that of other effects, including molecular Rayleigh scattering, surface reflection, gaseous absorption and aerosol and cloud scattering. AAI is a unitless quantity, positive values of AAI indicating the presence of  absorbing aerosols in the atmosphere. It should be noted, however, that AAI values depend on several factors, e.g. the amount of absorbing aerosols and aerosol layer height. This should be considered when comparing e.g. different episodes.  

The AAI observations can be used to study 

• Transport of smoke from fires, combined e.g. with IASI CO
• Dust storms
• Dispersion of ash from volcanic episodes
• Air quality events where absorbing aerosols are present

From GOME-2 observations AAI is provided as Offline Level 2 data, disseminated via Finnish Meteorological Institute data service. There are two kind of products available, "AAI" and "AAI from PMDs", that differ by their spatial resolution.  The Spatial resolution of "AAI" is equal to the spatial resolution of the GOME-2 instruments: 40 km x 40 km for Metop-A and 80 km x 40 km for Metop-B. The spatial resolution of AAI from the Polarisation Measurement Detectors (PMDs) is equal to the spatial resolution of the small field-of-view PMD detectors: 5 km x 40 km for Metop-A and 10 km x 40 km for Metop-B.