Measurement of deep-ultraviolet cross-sections of strongly absorbing atmospheric species and their potential for trace gas detection

Absorption in the deep-UV region often excites strong electronic bands. In cases where vibronic structure is evident, these strong absorptions could be exploited for sensitive and selective quantification of trace gases, as is done in long-path DOAS systems to monitor ammonia emissions. Accurate and appropriate resolution absorption cross sections are essential for this purpose, but literature cross sections of adequate quality are not always available. In this study, we report new cross section for major inorganic species (NO and SO₂), as well as important biogenic and anthropogenic volatile organic compounds (BVOC and AVOC). 
A spectrometer using a xenon arc flashlamp was used to measure absorption spectra in the wavelength range of 197 to 225 nm. Absorption cross section measurements using a flow cell were validated against SO₂ absorption cross-sections, for which there is excellent agreement in the literature. We report a new absorption cross section of nitric oxide (NO) using the flow cell. Despite being a key nitrogen oxide species in the atmosphere, there are few NO absorption cross-sections between 190 and 230 nm and little agreement among the spectra. VOCs measurements were made in a static cell and validated against the isoprene absorption cross-section. New absorption cross sections are reported for important AVOCS (benzene, toluene, ethylbenzene, xylene) and key BVOCS (α-pinene, β-pinene, limonene, 3-carene, and myrcene). The measured absorption cross-sections are compared and discussed.
We discuss the potential and challenges of using deep-UV measurements and the sensitivities that would be needed to be useful for trace gas detection in a range of contexts.