Sulfur isotopes ratio of atmospheric carbonyl sulfide constrains its sources

Alon Angert,Chen Davidson,Ward Said-Ahmad,Alon Amrani

doi:10.1038/s41598-018-37131-3

Alon Angert, Chen Davidson + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-37131-3

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Journal: Scientific Reports	Publication Date: Jan 24, 2019
Citations: 12	License type: open-access

Affiliation: Hebrew University of Jerusalem

Abstract

Carbonyl sulfide (COS) is the major long-lived sulfur bearing gas in the atmosphere, and is used to estimate the rates of regional and global (both past and current) photosynthesis. Sulfur isotope measurements (34S/32S ratio, δ34S) of COS may offer a way for improved determinations of atmospheric COS sources. However, measuring the COS δ34S at the atmospheric concentrations of ~0.5 ppb is challenging. Here we present high-accuracy δ34S measurements of atmospheric COS done by gas chromatograph (GC) connected to a multicollector inductively coupled plasma mass spectrometer (MC-ICPMS), after pre-concentrating from 2-liters of air. We showed that the precision of COS δ34S measurement for gas standards is ≤0.2‰, and that N2 and CO2 in the gas standard mixture had no effect on the measured δ34S. Natural air samples were collected in Israel and in the Canary Islands. The COS δ34S values in both locations were found to be 13.2 ± 0.6‰, and are believed to represent the background tropospheric value. This δ34S value is markedly different from the previously reported value of 4.9‰. We estimate the expected isotopic signature of COS sources and sinks, and use the δ34S value of atmospheric COS we measured to estimate that ~48% of it originates from the ocean.

Highlights

The atmosphere contains about 0.5 ppb carbonyl sulfide (COS), with a lifetime of few years[1]
A recent method of Carbonyl sulfide (COS) δ34S analysis on fragments ions using a pre-concentration air system coupled with isotope ratio mass spectrometer (IRMS) requires 10’s nmol which translates to hundreds of liters of air per analysis[15]
Other gases are not expected to interfere in COS trapping on Tenax because they are in trace amounts in the atmosphere, and even if captured by the Tenax, they will be separated by the gas chromatograph (GC) column

Summary

Introduction

The atmosphere contains about 0.5 ppb carbonyl sulfide (COS), with a lifetime of few years[1]. The contribution of each COS source to the atmosphere can be calculated using the appropriate isotope mass balance equations, and knowledge on the fractionation during uptake by the sinks (mainly plants, and atmospheric oxidation and soils). A recent method of COS δ34S analysis on fragments ions using a pre-concentration air system coupled with isotope ratio mass spectrometer (IRMS) requires 10’s nmol which translates to hundreds of liters of air per analysis[15]. With this method these researchers were able to provide a single δ34S value of COS of a compressed air sample from one location in Japan (Kawasaki). The need for hundreds of liters of air per analysis still limits the applicability of this method

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Conclusion