First Validation of Tropospheric NO2 Column Densities Retrieved from GOME by in situ Aircraft Profile Measurements

Tropospheric NO₂ columns retrieved from GOME were compared to column densities derived from aircraft NO₂ profile measurements. For a case study with clear sky conditions in central Europe, a very good agreement was found between the two methods. The in situ measurements yield a tropospheric NO₂ column of (4.2 ± 1.7)·x 1015 molec./cm2, whereas the GOME data result in columns of (3.5 ± 0.9) ·x 1015 molec./cm2 for near-real-time and (4.1 ± 1.0)·x 1015 molec./cm2 and dedicated analyses. The most important uncertainty in this study for the NO₂ columns from the aircraft measurements is caused by the lack of data in the lower boundary layer. The uncertainties for the GOME columns in this case are dominated by the assumptions made for the air-mass 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 by the aircraft is needed.