Formaldehyde (HCHO) is a significant constituent of the atmospheric chemistry involved in a lot of chemical reactions,
which principal global source is the intermediate oxidation of volatile organic compounds (VOCs). Taking into account
that HCHO basically undergo by photolysis and reaction with hydroxyl radical within a few hours, isoprene together
with other short-lived VOCs and direct HCHO emissions can cause local HCHO enhancement over certain areas, and,
hence, cases with HCHO, that exceed some background level, can be examined as local pollution of the atmosphere by
HCHO has significant specific features in spectral structure of UV absorption cross-section to be measured using the
differential optical absorption spectroscopy (DOAS) technique. Several retrieval algorithms applicable for DOAS
measurements in cloudless were previously developed. A new algorithm applicable for overcast and cloudless sky and its
error analysis is briefly presented in this paper.
In case we know the cloud base height, but don’t know cloud optical depth, the error of HCHO total content retrieval is
about 10-20% for winter season, about 5% for summer season, and about 30-40% for transition season when the ABL is
below the cloud base. In case we know both the cloud base height and cloud optical depth, the error is about 5-10% for
winter season, less than 5% for summer season, and about 25-35% for transition season when the ABL is below the
cloud base. The errors dramatically increase when clouds penetrate into ABL in both cases.