From OMI to TROPOMI: entering the realm of air quality from space

The Ozone Monitoring Instrument (OMI) on NASA's AURA satellite is one of the first instruments measuring an extensive set of daily air quality parameters from space. This anwers to a growing interest in obtaining space data for the air we breath next to the higher altitude air masses. OMI combines UV-Visible nadir viewing spectroscopy, small ground pixels and daily global coverage. As SCIAMACHY on ENVISAT, it uses the high sensitivity of UV-Visible spectroscopy to the lowest kilometers of the atmosphere and the boundary layer. It has fairly small ground pixels (13 × 24 km2) to allow for a high fraction of cloudfree observations and to help to observing detailed spatial features. Daily measurements form a prerequisite for air quality data. This paper shows examples of OMI air quality measurements and it explains in what sense these measurements can be improved. This makes use of the results of a study in the Netherlands on air quality user requirements and instrument design for an OMI/SCIAMACHY follow-on instrument. The improvements are implemented in a new instrument, TROPOMI: an O2A channel is added to improve on surface and cloud albedo, cloud fraction and cloud top height and a new separate module is added for the SWIR wavelengths for measuring CO and CH4. The ground pixel is reduced to 10 × 10 km2 and signal-tonoises are improved to allow measurements in low albedo areas. The design makes use of newly developed detectors and new optics to reduce the overall instrument size. Lastly, the paper discusses the problem of data continuity for the coming 10-15 years, i.e. after AURA and ENVISAT end of life.