Large-volume air sample system for measuring <sup>34</sup>S∕<sup>32</sup>S isotope ratio of carbonyl sulfide
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Published:2019-02-22
Issue:2
Volume:12
Page:1141-1154
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Kamezaki Kazuki, Hattori ShoheiORCID, Bahlmann EnnoORCID, Yoshida NaohiroORCID
Abstract
Abstract. Knowledge related to sulfur isotope ratios of carbonyl sulfide (OCS or COS),
the most abundant atmospheric sulfur species, remains scarce. An earlier
method developed for sulfur isotopic analysis for OCS using S+
fragmentation by an isotope ratio mass spectrometer is inapplicable for
ambient air samples because of the large samples required (approx. 500 L of
500 pmol mol−1 OCS). To overcome this difficulty, herein we present a
new sampling system for collecting approximately 10 nmol of OCS from ambient
air coupled with a purification system. Salient system features are
(i) accommodation of samples up to 500 L (approx. 10 nmol) of air at
5 L min−1; (ii) portability of adsorption tubes (1∕4 in. (0.64 cm)
outer diameter, 17.5 cm length, approximately 1.4 cm3 volume) for
preserving the OCS amount and δ34S(OCS) values at −80 ∘C
for up to 90 days and 14 days; and (iii) purification OCS from other
compounds such as CO2. We tested the OCS collection efficiency of
the systems and sulfur isotopic fractionation during sampling. Results show
precision (1σ) of δ34S(OCS) values as 0.4 ‰ for
overall procedures during measurements for atmospheric samples. Additionally,
this report presents diurnal variation of δ34S(OCS) values
collected from ambient air at the Suzukakedai campus of the Tokyo Institute
of Technology located in Yokohama, Japan. The observed OCS concentrations and
δ34S(OCS) values were, respectively, 447–520 pmol mol−1 and
from 10.4 ‰ to 10.7 ‰ with a lack of diurnal variation. The
observed δ34S(OCS) values in ambient air differed greatly from
previously reported values of δ34S(OCS) = (4.9±0.3) ‰ for compressed air collected at Kawasaki, Japan, presumably
because of degradation of OCS in cylinders and collection processes for that
sample. The difference of atmospheric δ34S(OCS) values between
10.5 ‰ in Japan (this study) and ∼13 ‰ recently
reported in Israel or the Canary Islands indicates that spatial and temporal
variation of δ34S(OCS) values is expected due to a link between
anthropogenic activities and OCS cycles. The system presented herein is
useful for application of δ34S(OCS) for investigation of OCS
sources and sinks in the troposphere to elucidate its cycle.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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