21.09.2004, Atmos. Chem. Phys. Discuss., 4, 5515-5548, 2004

Using photochemical models for the validation of NO2 satellite
measurements at different solar zenith angles

A. Bracher, M. Sinnhuber, A. Rozanov, J. P. Burrows

Abstract: SCIAMACHY (Scanning Imaging Spectrometer for Atmospheric Chartography) aboard the recently launched Environmental Satellite (ENVISAT) of ESA is measuring solar radiance upwelling from the atmosphere and the extraterrestrial irradiance. Appropriate inversion of the ultraviolet and visible radiance measurements, observed from the 5 atmospheric limb, yields profiles of nitrogen dioxide, NO 2 , in the stratosphere. In order to assess their accuracy, the resulting NO 2 profiles have been compared with those retrieved from the space borne occultation instruments Halogen Occultation Experiment (HALOE, data version v19) and Stratospheric Aerosol and Gas Experiment II (SAGE II, data version 6.20). As the HALOE and SAGE II measurements are performed during 10 local sunrise or sunset and because NO 2 has a significant diurnal variability, the NO 2 profiles derived from HALOE and SAGE II have been transformed to those predicted for the solar zenith angles of the SCIAMACHY measurement by using a 1-D photochemical model. The model used to facilitate the comparison of the NO 2 profiles from the different satellite sensors is described and an error assessment provided. Comparisons 15 between NO 2 profiles from SCIAMACHY and those from HALOE NO 2 but transformed to the SCIAMACHY solar zenith angle, for collocations from July to October 2002, show good agreement (within +/ - 15%) between the altitude range from 22 to 33 km. The results from the comparison of all collocated NO 2 profiles from SCIAMACHY and those from SAGE II transformed to the SCIAMACHY solar zenith angle show a systematic 20 negative bias of 10 to 35% between 20 km to 38 km with a small standard deviation between 5 to 14%. These results agree with those of Newchurch and Ayoub (2004), implying that above 20 km NO 2 profiles from SAGE II sunset are probably somewhat high.

Full Paper available in ACPD (click here)