First comparison of tropospheric NO2 column densities retrieved from GOME measurements and in situ aircraft profile measurements

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Abstract
For the first time tropospheric NO2 columns from GOME were compared to tropospheric columns derived from in situ measurements with the DLR research aircraft Falcon on a clear day above Austria. Under these conditions the agreement between the two methods is very good. The in situ measurements yield a tropospheric NO2 column of (4.2 ± 1.7)·1015 molec./cm2, whereas the GOME data result in columns of (3.5 ± 0.9)·1015 molec./cm2 and (4.1 ± 1.0)·1015 molec./cm2 for near‐real‐time and dedicated analyses, respectively. The most important uncertainty of the aircraft measurements is caused by the lack of data in the lower boundary layer. The GOME uncertainties in this particular case are dominated by the assumptions made for the airmass factor calculation. This work is the first independent validation of tropospheric NO2 columns from satellite instrumentation. Further validation at other seasons, and regions, including a more comprehensive sampling of the boundary layer is needed.