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Analysis of differential absorption techniques for formaldehyde monitoring in the ultraviolet spectral region

In response to the increasing interest in formaldehyde production, emission and photochemistry in polluted and clean atmospheres, we investigate the possibility to detect formaldehyde (CH2O) by the use of differential absorption Lidar (DIAL) techniques. In the first part of our investigations we review chemical and spectroscopic characteristics of formaldehyde with special respect to obtain the absorption and the differential absorption cross sections of the A1A2 - X1A1 vibrational band extended over the range of 250 nm - 360 nm. Four pairs of wavelengths, 321.2 nm/323.2 nm, 351.2 nm/352.9 nm, 307.8 nm/309.3 nm and 287.4 nm/288.8 nm, turn out to be adequate for remote mapping of atmospheric formaldehyde by differential absorption Lidar systems because of their large differential absorption cross sections and their absorption line profiles. In addition no interferences of the wavelengths of interest with the absorption of other atmospheric constituents is found. In a simulation study, where we use different set of DIAL-system- and spectroscopic input parameters, a formaldehyde detection limit of 1 - 5 ppb in clean air is predicted.