Studying trends in aerosol presence using the Absorbing Aerosol Index derived from GOME-1, SCIAMACHY, and GOME-2

In this paper we study 16-year long time series of the Absorbing Aerosol Index (AAI) for a selection of the most prominent aerosol producing regions on the globe. The time series of the AAI were recorded by the satellite instruments GOME-1, SCIAMACHY, and GOME-2 aboard the ERS-2, Envisat, and MetOp-A satellites, respectively. These three satellite instruments suffer, each in their own way, from severe instrument degradation in the ultraviolet (UV) wavelength range from which the AAI is derived. To be able to perform a reliable analysis on the AAI time series, we first remove the effects of instrument degradation from the Earth reflectances before calculating the AAI from them. To study the resulting time series, we use tropospheric NO2 data as a reference in the regions dominated by biomass burning events. It is found that the regional AAI data follow the regional tropospheric NO2 data well. Therefore, it is possible to accurately remove the effects of instrument degradation and to combine the AAI data from the three satellite instruments. The time series of the AAI for the studied aerosol regions show no clear trend over the studied 16-year time period from 1995 to 2011.