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Abstract
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 inter-calibrated instruments. Since November 2007 multi-axis differential optical absorption spectroscopy (MAX-DOAS) 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 O2-O2 differential slant columns and radiation intensity which depend both 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 will take place in Cabauw, in June and July 2009. Many different groups intend to participate in this campaign which will result in a variety of simultaneous in-situ and remote sensing observations of NO2.