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Absorption cross‐section measurements of water vapour and oxygen at 185 nm. Implications for the calibration of field instruments to measure OH, HO 2 and RO 2 radicals
Author(s) -
Creasey David J.,
Heard Dwayne E.,
Lee James D.
Publication year - 2000
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 - 10.1029/1999gl011014
Subject(s) - absorption cross section , water vapor , photodissociation , actinometer , analytical chemistry (journal) , radical , calibration , absorption (acoustics) , oxygen , materials science , chemistry , cross section (physics) , optics , photochemistry , environmental chemistry , physics , plasma , nuclear physics , organic chemistry , quantum mechanics
Absorption cross sections for oxygen and water vapour were measured using a low‐pressure mercury lamp optically filtered to isolate the emission close to 184.9 nm. The cross‐sections were determined for conditions typically used in the calibration of OH, HO 2 and RO 2 field instruments that employ photolysis of water vapour as a radical source, and O 2 absorption as the actinometer for lamp flux. For water vapour, an absorption cross‐section of 7.22 (± 0.22) × 10 −20 cm² molecule −1 was determined at 25°C, in excellent agreement with recent studies, but ∼30% higher than the recommended value. The absorption cross‐section for O 2 was found to vary with the O 2 column and the choice and operating current of the lamp, reinforcing the requirement that practitioners of OH, HO 2 and RO 2 field measurements who calibrate by this method should measure effective O 2 cross‐sections at frequent intervals under their particular field conditions.