Tropospheric Nitrogen Dioxide derived from Satellite Observations

A contribution to ACCENT-TROPOSAT-2, Task Group 1

Henk Eskes

KNMI, Atmospheric Composition Research Division, Postbus 201, 3730 AE De Bilt, Netherlands
Tel:  +31-(0)30-2206352
 Fax: +31-(0)30-2210407

The UV-Visible spectrometers GOME and SCIAMACHY have uniquely demonstrated the capability to observe chemicals in the lower troposphere (boundary layer). In particular the key chemical component nitrogen dioxide (NO2) can be measured with a high signal to noise ratio. The 8 years of NO2 measurements of GOME have provided detailed information on the year-to-year and seasonal variability, as well as observations of emission events and long-range transport plumes. A disadvantage of GOME is the relatively course resolution of 320x40 km. SCIAMACHY largely improves this with a  60x40 km footprint, which allows to determine integrated NO2 amounts originating from the major cities. Because the presence of clouds  severely limits an accurate retrieval of tropospheric NO2, in practice SCIAMACHY has a tropospheric global coverage roughly only once per month. Because of the daily global coverage OMI on EOS-AURA (launch mid 2004) will provide new information every few days with unprecedented spatial resolution.

A major challenge is the derivation of high quality quantitative tropospheric NO2 column amounts for individual ground pixels based on the satellite data. The retrieval of tropospheric trace gas species is characterised by large uncertainties, related to clouds, the surface albedo, the trace gas profile, the stratospheric column of NO2 , and aerosols. Estimates of the retrieval uncertainties due to these aspects is non-trivial.

The retrieval of NO2 is based on a combined retrieval, chemistry modelling and assimilation approach [Boersma and Eskes, JGR, 2004] and addresses these challenges. A chemistry-transport model, driven by realistic meteorological fields, provides best-guess profiles of NO2, based on the latest emission inventories, atmospheric transport, photochemistry, lightning modelling and wet/dry removal processes. These model forecast fields are collocated with the satellite observations, and the radiative transfer modelling in the retrieval is performed for individual pixels based on the model trace gas profile and temperature profiles. The stratospheric NO2 distribution is obtained from the assimilation of the NO2 observations with the chemistry-transport model. This stratospheric distribution is employed to derive a tropospheric column by subtracting the modelled (assimilated) stratosphere from the measured column. The retrieval is coupled to cloud top height and cloud fraction retrievals derived from the GOME, SCIAMACHY or OMI data.

Retrievals of tropospheric NO2 from GOME have been performed in collaboration with the Heidelberg group of U. Platt in the context of the European project GOA, “GOME Assimilated and Validated Ozone and NO2 Fields for Scientific Users and for Model Validation”. Results are available on the GOA web site, http://www.knmi.nl/goa/. SCIAMACHY NO2 retrievals, performed in collaboration with the BIRA group (M. van Roozendael, I. Desmedt) are available from the TEMIS website, http://www.temis.nl/.

Time Schedule

 

2004

2005

2006

2007

Tropospheric NO2 retrieval for GOME, SCIA, OMI

*

*

*

*

Approximate manpower and cost

 

2004

2005

2006

2007

Personnel / man-years

1

2

2

2

Yearly cost (k€)

5

10

10

10

Reported costs are travel expenses only

Likely funding agencies

This work has been funded through the Dutch National User Support Programme (USP), the ESA DUP project TEMIS and the EU project GOA. We aim to acquire further support from USP, ESA or EU FP6.

Co-workers

Folkert Boersma, Ellen Brinksma and Ronald van der A.

 


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