Scientists identify missing source of atmospheric carbonyl sulfide
Study provides better understanding of plants' carbon uptake

Date:
August 6, 2020
Source:
Tokyo Institute of Technology
Summary:
Researchers report that anthropogenic sources of carbonyl sulfide
(OCS), not just oceanic sources, account for much of the missing
source of OCS in the atmosphere. Their findings provide better
context for estimates of global photosynthesis (taking up CO2)
using OCS dynamics.



FULL STORY ========================================================================== Researchers at Tokyo Institute of Technology (Tokyo Tech) report that anthropogenic sources of carbonyl sulfide (OCS), not just oceanic sources, account for much of the missing source of OCS in the atmosphere. Their
findings provide better context for estimates of global photosynthesis
(taking up CO2) using OCS dynamics.


========================================================================== Carbonyl sulfide (OCS) is the most stable and abundant sulfur-containing
gas in the atmosphere. It is derived from both natural and anthropogenic sources and is of key interest to scientists investigating how
much carbon dioxide (CO2) plants take out of the atmosphere for
photosynthesis. Measuring CO2 alone cannot provide estimates of
photosynthesis (taking up CO2) because plants also release CO2 through respiration. In contrast, OCS is taken up like CO2 but is not released
by respiration, and can therefore provide valuable information about
the rate of global photosynthesis.

Understanding the precise OCS budget (the balance of source and sink)
is an ongoing challenge. The most critical point of uncertainty related
to the OCS budget is its missing source. Lack of observational evidence
has so far led to debate about whether the missing OCS source is oceanic
or anthropogenic emission.

In a new study published in Proceedings of the National Academy of
Sciences (PNAS), researchers from Tokyo Tech's School of Materials and
Chemical Technology and Earth-Life Science Institute (ELSI) have used
a unique method of measuring sulfur isotope ratios (minor 34S isotope
abundance relative to major isotope 32S, 34S/32S) of OCS that enabled
them to distinguish oceanic and anthropogenic OCS sources.

"It's very exciting that we were able to separate anthropogenic and
oceanic signals for OCS sources based on sulfur isotope ratios," says
Shohei Hattori, an assistant professor at Tokyo Tech and lead author of
the study. "These measurements required at least 200 liters of air for
each sample measurement.

We overcame this challenge by developing a new sampling system,
and eventually succeeded in measuring sulfur isotope ratios of the
atmospheric OCS." The team found a north-south latitudinal gradient in
the 34S isotope abundance corresponding to OCS concentrations during
wintertime in eastern Asia. Their results provide evidence of the
importance of anthropogenic OCS emissions from China. Also, by using
the sulfur isotope level of OCS as a new constraint, they found that anthropogenic OCS sources, and not only oceanic sources, are likely to
be major constituents of the missing source of atmospheric OCS.

"The higher relevance of anthropogenic OCS at mid-to-low latitudes has implications for understanding climate change and stratospheric chemistry
in both past and future contexts," says co-author Kazuki Kamezaki.

Given that the historical estimation of how much CO2 is taken up by plants
is sensitive to the estimate of the anthropogenic OCS inventory, a more detailed picture of the OCS budget revealed by sulfur isotopic approach
will enable more precise estimation of its interactions with global
change. The research team will continue to undertake more observations
to make detailed quantitative estimates and predictions of the global photosynthesis rate.

"Our sulfur isotopic approach for measuring atmospheric OCS is an
important step, but more observations, together with analysis using a
chemical transport model, will enable detailed quantitative conclusions," Hattori says.


========================================================================== Story Source: Materials provided by Tokyo_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Shohei Hattori, Kazuki Kamezaki, Naohiro Yoshida. Constraining the
atmospheric OCS budget from sulfur isotopes. Proceedings
of the National Academy of Sciences, 2020; 202007260 DOI:
10.1073/pnas.2007260117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200806122809.htm

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