Global observations and spectral characteristics of desert dust and biomass burning aerosols

A technique that has gained considerable interest over the last years to monitor aerosol distributions and characterise aerosol source regions has been the use of the absorbing aerosol index (AAI). It has been used extensively to monitor ultraviolet (UV) absorbing aerosols, mainly desert dust and biomass burning aerosols. The AAI is not an aerosol quantity, but a radiation difference in the UV. Its main advantages are its insensitivity to scattering aerosols and clouds, which makes it suitable for global monitoring of absorbing aerosols with sensors with large footprints, and its insensitivity to surface type, which makes it suitable for monitoring aerosols over both sea and land and to study the source regions of UV-absorbing aerosols, which are mainly over land. The European spectrometers GOME and SCIAMACHY have been used to produce daily AAI distributions. GOME data (July 1995-December 2000) have been used to validate the TOMS AAI distributions and complement the TOMS data set in the period July 1995-October 1996, when no TOMS data are available. SCIAMACHY has been measuring from July 2002 to present. The spectrometers measure the entire spectrum from about 240 nm to about 800 nm (GOME) or about 2400 nm (SCIAMACHY). These instruments are used to characterise the spectra of desert dust and biomass burning aerosols scenes. The spectra are used to discriminate between these aerosol types using direct measurements, which can be useful for aerosol retrieval algorithms which at present use aerosol composition climatologies.