Interhemispheric ratio and annual cycle of carbonyl sulfide (OCS) total column from ground‐based solar FTIR spectra

Abstract

Abstract. We have made extensive measurements of total column OCS by ground-based highresolution solar Fourier transform infrared absorption spectroscopy from two southern hemisphere sites to complement earlier measurements in the northern hemisphere and to investigate the interhemispheric ratio, variability, and seasonal cycles of OCS in the atmosphere. The measurements were made at Lauder, New Zealand (45.0øS, 169.7øE, 370 rn asl, 547 spectra March 1993 through April 1997), and Wollongong, Australia (34.45øS, 150.88øE, 30 rn asl, 358 spectra May 1996 through April 1997). The annual mean column amounts are 9.15 x 10 •5 molecules cm -2 above Lauder and 9.84 x 10 •5 molecules cm -2 above Wollongong, corresponding to tropospheric mixing ratios of 480 and 490 parts per trillion by volume, respectively, with the assumed mixing ratio vertical profiles. The secular trend in total column OCS is less than 1% per year. Variability of all measurements about the means implies an atmospheric lifetime for OCS of at least 2.8 years. Comparison with earlier measurements in the northern hemisphere yields a north/south interhemispheric ratio in the range 1.1-1.2. There are peak-to-peak apparent annual cycles in total column OCS of 6% at Lauder and 18% at Wollongong with a late summer maximum. Seasonal tropopause height variation accounts for a 5-6% amplitude, and the remainder of the amplitude in Wollongong is assumed to be due to changes in the tropospheric mixing ratio.

Long‐term trends of inorganic chlorine from ground‐based infrared solar spectra: Past increases and evidence for stabilization

“…Measurements of ClONO 2 have been markedly improved since August 1999 by the use of narrower optical filters covering the region below 1000 cm À1 . Additional observational details have been reported previously [Griffith et al, 1998;Rinsland et al, 2001].…”

“…The instrument was replaced with a Bomem DA-8 in May 1996 and used at 0.004-cm À1 resolution (250 cm OPD) [Griffith et al, 1998]. The site is on the University of Wollongong campus on the Australian east coast.…”

Positive trends in Southern Hemisphere carbonyl sulfide

“…differ [Campbell et al, 2008;Sandoval-Soto et al, 2005;Suntharalingam et al, 2008], and therefore, large uncertainties in the OCS budget remain [Kettle et al, 2002;Montzka et al, 2007] [Griffith et al, 1998;Kohlhepp et al, 2012;Paton-Walsh et al, 2004]. To ensure that differences in OCS behavior across the three sites are unaffected by the configuration of the retrieval, the same retrieval settings were used at all three sites, i.e., fitting four microwindows covering the p19 (2053.98-2054.24 [Rinsland et al, 1998]) is designed to retrieve vertical profiles of one or more gases from solar absorption FTS spectra.…”

Trace gas emissions from biomass burning inferred from aerosol optical depth

“…The tracker has both active and passive tracking systems and is able to follow the sun through smoke plumes that are opaque to the human eye. Spectra were recorded in a number of regions of the infrared from 700 cm À1 to 4500 cm À1 using Mercury Cadmium Telluride and Indium Antimonide detectors, and a series of eight different optical band pass filters [Griffith et al, 1998]. The number of molecules per square centimetre above the measurement site (the vertical column amounts) of carbon monoxide (CO), ammonia (NH 3 ), formaldehyde (H 2 CO) and hydrogen cyanide (HCN) were derived from individual spectra from the appropriate filter regions, using the iterative fitting algorithm known as SFIT2 [Rinsland et al, 1998].…”