Open AccessHO cycle in 1997 and 1998 over the southern Indian Ocean derived from CO, radon, and hydrocarbon measurements made at Amsterdam Island
Author(s) -
Williams J.,
Gros V.,
Bonsang B.,
Kazan V.
Publication year - 2001
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd900116
Subject(s) - relative humidity , environmental science , seasonality , atmospheric sciences , radon , hydrocarbon , climatology , meteorology , geology , chemistry , physics , mathematics , statistics , organic chemistry , quantum mechanics
A new empirical method for the derivation of average HO radical concentrations is presented. The method is based on estimation of CO lifetime through the relative variability of CO and Rn measurements, and hydrocarbon measurements are used to independently determine the relative effects of chemistry and dynamics. Data from Amsterdam Island (37°S, 77°E), a remote site in the southern Indian Ocean, are used to calculate annual and daily HO levels for 1997 and 1998. A seasonal variation in calculated daily HO, consistent with seasonally changing photolysis rates, with maxima in summer and minima in winter is also derived which is comparable but slightly lower than the most recent zonal mean HO estimates of Spivakovsky et al. [2000]. The calculated annual HO shows a decrease from 2.7×10 5 molecule cm −3 in 1997 to 0.8×10 5 molecule cm −3 in 1998, possibly as a result of El Niño related meteorological changes. The empirically calculated HO correlates with temperature and relative humidity measured at the island but anticorrelates strongly with CO and to a lesser extent with O 3 . The limitations and improvements to this method are discussed. The method has potential for long‐term monitoring of HO changes over areas upwind from remote sites.