Laser-induced fluorescence instrument for the detection of NO₂ and thermal dissociation measurement of PAN and N₂O₅

The Harvard NO₂ instrument uses laser-induced fluorescence (LIF) for the direct detection of NO₂ without requiring chemical titration or processing. Excitation of a spectrally narrow (0.04 cm^-1) feature in the NO₂ spectrum at 585 nm allows for the highly selective detection of NO₂ distinct from other potential interferences such as N₂-Raman scattering, chamber scatter, and other unstructured fluorescence. The conversion of the NO₂ fluorescence signal to absolute NO₂ concentration requires a combination of laboratory and in-flight calibrations. In regions of the upper troposphere and TTL, in which strong convection may occur, the combination of vertical and horizontal transport demanding in situ measurements of peroxyacetylnitrate (PAN) and other peryoxy nitrates (PNs), which constitute significant NO_x reservoir species, it is important in order to determine how much they are transported into the upper troposphere and TTL, especially during convective events.