Atmospheric chemistry nadir observation from space now spans nearly forty years. The early UVN (UV nadir missions) mainly focused on measuring ozone. The selected wavelengths between 250 and 360 nm measured by the series of SBUV (Solar Backscatter Ultraviolet) and TOMS (Total Ozone Mapping Spectrometer) permitted in addition to ozone, detection of SO2 as well as aerosol extinction. The introduction of DOAS (Differential Optical Absorption Spectroscopy) type UVN instruments in 1995 (GOME: Global Ozone Monitoring instrument) with larger and continuous spectral coverage extended largely the list of observable atmospheric trace gases that also include BrO, NO2, OClO, H2CO, glyoxal, water vapor, IO. Nadir observations in generally provide only column information (total column, vertical column density) from trace gases, but sophisticated retrieval schemes permit the separation of tropospheric (up to about 8-15 km) and stratospheric contents (above 15 km). Vertically resolved ozone profiles can be derived from the UV absorption edge (about 8 km vertical resolution). Additionally the UVN sensors provide information on aerosols and clouds.
The combination of UVN observations from different missions now allows the detection of decadal trends in atmospheric constituents and aerosols that are relevant to climate change and air quality. Natural processes like volcanic emissions (SO2, aerosols) play an important role and their impact our climate can be investigated.
The main scientific achievements from UVN are in the area of:
Stratospheric ozone dynamics and chemistry (recovery of the ozone layer and climate interaction)
Air quality (atmospheric lifetime of reactive species, regional distribution and transport, chemistry)
Natural emission and hazards
Cloud and aerosol physics and chemistry
Mark Weber (U. Bremen)
Udo Friess (U. Heidelberg), Diego Loyola (DLR), Thomas Wagner (MPIC)