Impact of albedo and cloud retrievals on the NO2 tropospheric column derived from Sentinel-5P TROPOMI observations

Sentinel-5P, with the TROPOMI instrument, was launched in October 2017 and is providing unique high-quality and high-resolution (5 km) observations of trace gas pollutants with a daily global coverage. In our contribution we will discuss the retrieval of nitrogen dioxide (NO2). A major contributions to the total uncertainty of these measurements are the TROPOMI retrievals of cloud fraction and effective cloud pressure (or altitude). Several cloud retrieval algorithms have been implemented, deriving cloud height information from the near-infrared O2-A band, O2-B band or the O2-O2 absorption feature near 477nm. In our presentation we will show the importance of a consistent treatment of clouds and albedo as input for the retrieval radiative transfer calculations. The impact of the different cloud products on the retrieved NO2 is demonstrated for a new implementation of the FRESCO O2-A band cloud retrieval algorithm and an implementation of the O2-O2 retrievals for TROPOMI. A recipe to make optimal use of the available cloud information is presented.