Near-real time retrieval of tropospheric NO2 from OMI K. F. Boersma1,*, H. J. Eskes1, J. P. Veefkind1, E. J. Brinksma1, R. J. van der A1, M. Sneep1, G. H. J. van den Oord1, P. F. Levelt1, P. Stammes1, J. F. Gleason2, and E. J. Bucsela2 1KNMI, De Bilt, The Netherlands 2NASA GSFC, Greenbelt, MD, USA *now at: Harvard University, Cambridge, USA
Abstract. We present a new algorithm for the near-real
time retrieval – within 3 h of the actual satellite
measurement – of tropospheric NO2 columns from
the Ozone Monitoring Instrument (OMI). The retrieval is
based on the combined retrieval-assimilation-modelling
approach developed at KNMI for off-line tropospheric NO2
from the GOME and SCIAMACHY satellite instruments. We have adapted
the off-line system such that the required a priori information – profile shapes
and stratospheric background NO2 – is now immediately available upon arrival
(within 80 min of observation) of the OMI NO2 slant columns and cloud data at
KNMI. Slant columns for NO2 are retrieved using differential optical
absorption spectroscopy (DOAS) in the 405–465 nm range. Cloud fraction
and cloud pressure are provided by a new cloud retrieval algorithm that uses
the absorption of the O2-O2 collision complex near 477 nm.
On-line availability of stratospheric slant columns and NO2 profiles
is achieved by running the TM4 chemistry transport model (CTM) forward in
time based on forecast ECMWF meteo and assimilated NO2 information
from all previously observed orbits. OMI NO2 slant columns, after
correction for spurious across-track variability, show a random error for
individual pixels of approximately 0.7×1015 molec cm−2.
Cloud parameters from OMI's O2-O2 algorithm have similar frequency distributions as
retrieved from SCIAMACHY's Fast Retrieval Scheme for Cloud Observables (FRESCO) for August 2006.
On average, OMI cloud fractions are higher by 0.011, and OMI cloud pressures exceed FRESCO cloud pressures by
60 hPa. A sequence of OMI observations over Europe in October 2005 shows OMI's capability to track
changeable NOx air pollution from day to day in cloud-free situations.
Citation: Boersma, K. F., Eskes, H. J., Veefkind, J. P., Brinksma, E. J., van der A, R. J., Sneep, M., van den Oord, G. H. J., Levelt, P. F., Stammes, P., Gleason, J. F., and Bucsela, E. J.: Near-real time retrieval of tropospheric NO2 from OMI, Atmos. Chem. Phys., 7, 2103-2118, doi:10.5194/acp-7-2103-2007, 2007.