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Long‐path absorption measurements of tropospheric NO 2 in rural New Zealand
Author(s) -
Johnston P. V.,
McKenzie R. L.
Publication year - 1984
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl011i001p00069
Subject(s) - monochromator , absorption (acoustics) , troposphere , optics , signal (programming language) , materials science , amplitude , detector , remote sensing , environmental science , analytical chemistry (journal) , physics , atmospheric sciences , chemistry , geology , wavelength , chromatography , computer science , programming language
Tropospheric concentrations of nocturnal NO 2 measured at our rural site in New Zealand (45°S, 170°E) are presented. We also describe the long path spectroscopic absorption technique used. The system features a beam splitter just before the exit slit of a scanning monochromator, and the broad spectral band signal seen at a second detector is used to remove the effect of amplitude modulations caused by atmospheric flicker. A signal ratioing technique produces nearly 2 orders of magnitude improvement in this noise. With a one hour observation period detection thresholds of 20 ppt have been achieved from absorptions over a 9.2 km path. The results display a wide range of mixing ratios from the detection threshold, up to in excess of 1 ppb on isolated days. A strong absorption feature at 442.6 nm is identified as a water vapour absorption, and the absorption cross section is found to be (3.1±0.3) × 10 −26 cm² molecule −1 at 0.5 nm resolution.