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Impact of effective cloud fraction on tropospheric NO2 retrieval
Ping Wang(1), Piet Stammes(1)
, and Folkert Boersma(1)
(1)
Royal Netherlands Meteorological Institute (KNMI) ,
Wilhelminalaan 10,
NL-3732 GK De Bilt ,
Netherlands
Abstract
In general clouds have shielding, albedo and in-cloud absorption effects
on trace gas retrievals. To correct for these cloud effects the cloud
fraction and cloud altitude are two important parameters. The effective
cloud fraction is the cloud fraction of a Lambertan surface with
fixed albedo (e.g. 0.8) yielding the same radiance at the top of
atmosphere (TOA) as the cloud in the scene. The effective cloud fraction has been used in cloud correction of trace gas retrievals from GOME and SCIAMACHY.We simulated the impact of effective cloud fraction on tropospheric NO2 retrieval with the DAK model (Doubling Adding KNMI) by comparing the tropospheric NO2 air mass factors (AMFs) with Mie clouds with those of Lambertian clouds. We found that a Lambertian cloud with high albedo is a good assumption for cloud corrections. The tropospheric NO2 AMF differences between Mie cloud and Lambertian clouds of albedo 0.8 are within 10% if the geometric cloud fraction is smaller than 0.2.
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