Deep-ultraviolet absorption cross sections of strongly absorbing atmospheric species

Absorption of deep-ultraviolet photons gives rise to intense vibronic transitions in molecules and can be exploited for sensitive and selective quantification of trace gases. Accurate absorption cross sections at appropriate resolution are essential for such applications, but are not well characterised for even major atmospheric species like nitric oxide (NO) and key biogenic and anthropogenic volatile organic compounds (BVOCs and AVOCs). This study reports new absorption cross section spectra from 197 to 235 nm for NO at 1 atm and 293 K and important aromatic AVOCs (benzene, toluene, ethylbenzene, and o-, m-, and p-xylene) and BVOCs (α-pinene, β-pinene, limonene, 3-carene, and myrcene) at 1 atm across a temperature range of 293 K to 296 K. Measurements were made with a xenon flashlamp spectrometer using a flow cell configuration for gas mixtures and a static cell arrangement for vapour-phase VOC samples. The resolution of the spectrum at 253.7 nm was approximately 0.3 nm. Both configurations showed excellent agreement in magnitude and spectral features with well-established literature cross sections. Flow cell measurements were validated against the absorption cross section of sulfur dioxide (SO₂) and static cell measurements against that of isoprene. Our absorption cross sections of NO and m-xylene reconcile large differences in the magnitude and spectral structure of previous cross sections. The deep-UV absorption cross sections of 3-carene, myrcene and ethylbenzene are reported for the first time, and confirmed for α-pinene, β-pinene, and limonene. We discuss the potential and challenges of using deep-UV absorption for quantifying these gases ambient air monitoring, emissions monitoring, and breath analysis.