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 NOx reservoir species, it is important in order to determine how much they are transported into the upper troposphere and TTL, especially during convective events.