Operational total and tropospheric NO<sub>2</sub> column retrieval for GOME-2
This paper presents the algorithm for the operational near real time retrieval of total and tropospheric NO<sub>2</sub> columns from the Global Ozone Monitoring Experiment (GOME-2). The retrieval is performed with the GOME Data Processor (GDP) version 4.4 as used by the EUMETSAT Satellit...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2011-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/4/1491/2011/amt-4-1491-2011.pdf |
| Summary: | This paper presents the algorithm for the operational near real time retrieval of total and tropospheric NO<sub>2</sub> columns from the Global Ozone Monitoring Experiment (GOME-2). The retrieval is performed with the GOME Data Processor (GDP) version 4.4 as used by the EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M-SAF). The differential optical absorption spectroscopy (DOAS) method is used to determine NO<sub>2</sub> slant columns from GOME-2 (ir)radiance data in the 425–450 nm range. Initial total NO<sub>2</sub> columns are computed using stratospheric air mass factors, and GOME-2 derived cloud properties are used to calculate the air mass factors for scenarios in the presence of clouds. To obtain the stratospheric NO<sub>2</sub> component, a spatial filtering approach is used, which is shown to be an improvement on the Pacific reference sector method. Tropospheric air mass factors are computed using monthly averaged NO<sub>2</sub> profiles from the MOZART-2 chemistry transport model. An error analysis shows that the random error in the GOME-2 NO<sub>2</sub> slant columns is approximately 0.45 × 10<sup>15</sup> molec cm<sup>−2</sup>. As a result of the improved quartz diffuser plate used in the GOME-2 instrument, the systematic error in the slant columns is strongly reduced compared to GOME/ERS-2. The estimated uncertainty in the GOME-2 tropospheric NO<sub>2</sub> column for polluted conditions ranges from 40 to 80 %. An end-to-end ground-based validation approach for the GOME-2 NO<sub>2</sub> columns is illustrated based on multi-axis MAXDOAS measurements at the Observatoire de Haute Provence (OHP). The GOME-2 stratospheric NO<sub>2</sub> columns are found to be in good overall agreement with coincident ground-based measurements at OHP. A time series of the MAXDOAS and the GOME-2 tropospheric NO<sub>2</sub> columns shows that pollution episodes at OHP are well captured by GOME-2. Monthly mean tropospheric columns are in very good agreement, with differences generally within 0.5 × 10<sup>15</sup> molec cm<sup>−2</sup>. |
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| ISSN: | 1867-1381 1867-8548 |