| Volumes and Issues Contents of Issue 6 |
www.atmos-meas-tech-discuss.net/2/3221/2009/
doi:10.5194/amtd-2-3221-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
On the improvement of NO2 satellite retrievals – aerosol impact on the airmass factors
1Institute of Environmental Physics, University of Bremen, Bremen, Germany
2Laboratoire Inter-Universitaire des Systèmes Atmosphèriques (LISA), CNRS et Universités Paris 12 et Paris 7, Créteil, France
Abstract. The accurate determination of nitrogen dioxide (NO2) tropospheric vertical columns from satellite measurements depends, partly, on the airmass factor (AMF) used. A sensitivity study was performed with the radiative transfer model SCIATRAN to better understand the impact of aerosols in the calculation of NO2 AMFs. This influence was studied by varying the NO2 and aerosol vertical distributions, as well as physical and optical properties of the particles. The key factors for these calculations were identified as the relation between trace gas and aerosol vertical profiles, the optical depth of the aerosol layer, and single scattering albedo. Overall it was found that aerosol mixed with the trace gas increases the measurements' sensitivity. The largest change, a factor of ~2 relative to the situation without aerosols, was found when a low layer of aerosol (600 m) was combined with a homogenous NO2 layer of 1.0 km. A layer of aerosol above the NO2 will usually reduce the sensitivity of the satellite measurement, a situation found mostly for runs with discrete elevated aerosol layers representative for long-range transport of aerosols that can generate a decrease of the AMF values of up to 70%. The use of measured aerosol profiles and modelled NO2 resulted, generally, in a much smaller changes of AMF relative to the pure Rayleigh case. Exceptions are some events of elevated layers with high aerosol optical depth that lead to a strong decrease of the AMF values. These results highlight the importance of aerosols in the retrieval of tropospheric NO2 columns from space and indicate the need for detailed information on aerosol properties and vertical distribution.
Discussion Paper (PDF, 2364 KB) Interactive Discussion (Closed, 4 Comments) Final Revised Paper (AMT)
Citation: Leitão, J., Richter, A., Vrekoussis, M., Kokhanovsky, A., Zhang, Q. J., Beekmann, M., and Burrows, J. P.: On the improvement of NO2 satellite retrievals – aerosol impact on the airmass factors, Atmos. Meas. Tech. Discuss., 2, 3221-3264, doi:10.5194/amtd-2-3221-2009, 2009. Bibtex EndNote Reference Manager XML
