Atmospheric trace gases such as nitrogen dioxide (NO₂) may be measured by satellite instruments sensitive to solar ultraviolet–visible radiation reflected from Earth and its atmosphere. For a single pixel, clouds in neighbouring pixels may affect the radiation and hence the retrieved trace gas amount. We found that for a solar zenith angle less than about 40° this cloud-related NO₂ bias is typically below 10 %, while for larger solar zenith angles the NO₂ bias is on the order of tens of percent.