HO cycle in 1997 and 1998 over the southern Indian Ocean derived from CO, radon, and hydrocarbon measurements made at Amsterdam Island

Citation
J. Williams et al., HO cycle in 1997 and 1998 over the southern Indian Ocean derived from CO, radon, and hydrocarbon measurements made at Amsterdam Island, J GEO RES-A, 106(D12), 2001, pp. 12719-12725
Citations number
26
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Volume
106
Issue
D12
Year of publication
2001
Pages
12719 - 12725
Database
ISI
SICI code
Abstract
A new empirical method for the derivation of average HO radical concentrati ons is presented. The method is based on estimation of CO lifetime through the relative variability of CO and Rn measurements, and hydrocarbon measure ments are used to independently determine the relative effects of chemistry and dynamics. Data from Amsterdam Island (37 degreesS, 77 degreesE), a rem ote site in the southern Indian Ocean, are used to calculate annual and dai ly HO levels for 1997 and 1998. A seasonal variation in calculated daily HO , consistent with seasonally changing photolysis rates, with maxims in summ er and minima in winter is also derived which is comparable but slightly lo wer than the most recent zonal mean HO estimates of Spivakovsky et al. [200 0]. The calculated annual HO shows a decrease from 2.7 X 10(5) molecule cm( -3) in 1997 to 0.8 X 105 molecule cm(-3) in 1998, possibly as a result of E l Nino related meteorological changes. The empirically calculated HO correl ates with temperature and relative humidity measured at the island but anti correlates strongly with CO and to a lesser extent with O-3. The limitation s and improvements to this method are discussed. The method has potential f or long-term monitoring of HO changes over areas upwind from remote sites.