Characterisation of GOME-2 formaldehyde retrieval sensitivity

Formaldehyde (CH[subscript 2]O) is an important tracer of tropospheric photochemistry, whose slant column abundance can be retrieved from satellite measurements of solar backscattered UV radiation, using differential absorption retrieval techniques. In this work a spectral fitting sensitivity analysis is conducted on CH[subscript 2]O slant columns retrieved from the Global Ozone Monitoring Experiment 2 (GOME-2) instrument. Despite quite different spectral fitting approaches, the retrieved CH[subscript 2]O slant columns have geographic distributions that generally match expected CH[subscript 2]O sources, though the slant column magnitudes and corresponding uncertainties are particularly sensitive to the retrieval set-up. The choice of spectral fitting window, polynomial order, I[subscript 0] correction, and inclusion of minor absorbers tend to result in the largest modulations of retrieved slant column magnitude and fit quality. However, application of a reference sector correction using observations over the remote Pacific Ocean is shown to largely homogenise the resulting CH[subscript 2]O vertical columns obtained with different retrieval settings, thereby largely reducing any systematic error sources from spectral fitting.