MAX-DOAS aerosol corrected tropospheric vertical columns of nitrogen dioxide

Nitrogen Dioxide (NO2) is an important component of air pollution. It is observed on a global scale by satellite instruments such as GOME, SCIAMACHY and OMI. Worldwide there are only few observation sites where nitrogen dioxide tropospheric columns are monitored on an operational basis. For satellite validation it is essential to perform these ground based measurements with good global and seasonal coverage preferably in a network of similar and intercalibrated instruments. Since November 2007 multiaxis differential optical absorption spectroscopy (MAXDOAS) observations of NO2 are performed on an operational basis at the Royal Netherlands Meteorological Institute (KNMI). For this a Mini MAX-DOAS instrument is used. This relatively low cost instrument could be a candidate for a global network as mentioned above. We will explain the tropospheric column retrieval algorithm which includes a correction for aerosols. The Doubling Adding radiative transfer model is used to create look up tables for the Air Mass Factors as a function of radiation intensity which depends on aerosol optical thickness (AOT) and boundary layer height. In addition we will show results from several studies based on the observations. First: a comparison of retrieved AOT and direct sun observations of AOT from the CESAR site in Cabauw, The Netherlands. Second: an analysis of the retrieved tropospheric vertical columns of NO2 in this highly polluted region. Third: comparison with SCIAMACHY and OMI tropospheric NO2 columns. Finally: first results from the CINDI inter-comparison campaign for NO2 measuring instruments. This campaign has taken place in Cabauw, in June and July 2009. Many different groups have participate in this campaign which had resulted in a variety of simultaneous in-situ and remote sensing observations of NO2, other trace gases and aerosols.