Possible Breakthrough: Sulfate Aerosol Geoengineering from Earth's Surface

[Ron Baiman]

Dear Colleagues,

FYI, if you haven't heard or seen this. 

Carbonyl Sulfide (COS) aerosols released from the earth's surface and in models appear to have a cooling impact similar to SO2 released in the stratosphere. More research on the potential impacts of increased COS released from the surface into the troposphere, that (as I recall from the podcast) rises and stays in the stratosphere for an extended period of time, for example on soil and plant uptake is needed, but as Andrew opines, this method may be an "Sulfate Geoengineering COS Surface Radiative Forcing"  (SG-COS-SRF) surface aerosol release breakthrough as it requires no aviation (conventional or other) or advanced injection technology.

Listen here:

https://podcasts.apple.com/us/podcast/using-tropospheric-cos-emissions-for-srm-quaglia/id1529459393?i=1000565776236

Paper Abstract:

An approach to sulfate geoengineering with
surface emissions of carbonyl sulfide
Ilaria Quaglia1, Daniele Visioni2, Giovanni Pitari1, and Ben Kravitz3,4
1Department of Physical and Chemical Sciences, Università dell’Aquila, 67100 L’Aquila, Italy
2Sibley School for Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
3Department of Earth and Atmospheric Science, Indiana University, Bloomington, IN, USA
4Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory,
Richland, WA, USA
Correspondence: Ilaria Quaglia (ilaria....@aquila.infn.it)
Received: 29 September 2021 – Discussion started: 11 October 2021
Revised: 16 March 2022 – Accepted: 28 March 2022 – Published: 3 May 2022
Abstract. Sulfate geoengineering (SG) methods based on lower stratospheric tropical injection of sulfur dioxide
(SO2) have been widely discussed in recent years, focusing on the direct and indirect effects they would have on
the climate system. Here a potential alternative method is discussed, where sulfur emissions are located at the
surface or in the troposphere in the form of carbonyl sulfide (COS) gas. There are two time-dependent chemistry–
climate model experiments designed from the years 2021 to 2055, assuming a 40 Tg−S yr−1 artificial global flux
of COS, which is geographically distributed following the present-day anthropogenic COS surface emissions
(SG-COS-SRF) or a 6 Tg − S yr−1 injection of COS in the tropical upper troposphere (SG-COS-TTL). The
budget of COS and sulfur species is discussed, as are the effects of both SG-COS strategies on the stratospheric
sulfate aerosol optical depth (∼ 1τ = 0.080 in the years 2046–2055), aerosol effective radius (0.46 μm), surface
SOx deposition (+8.9 % for SG-COS-SRF; +3.3 % for SG-COS-TTL), and tropopause radiative forcing (RF;
∼ −1.5 W m−2 in all-sky conditions in both SG-COS experiments). Indirect effects on ozone, methane and
stratospheric water vapour are also considered, along with the COS direct contribution. According to our model
results, the resulting net RF is −1.3 W m−2, for SG-COS-SRF, and −1.5 W m−2, for SG-COS-TTL, and it is
comparable to the corresponding RF of −1.7 W m−2 obtained with a sustained injection of 4 Tg − S yr−1 in the
tropical lower stratosphere in the form of SO2 (SG-SO2, which is able to produce a comparable increase of the
sulfate aerosol optical depth). Significant changes in the stratospheric ozone response are found in both SG-COS
experiments with respect to SG-SO2 (∼ 5 DU versus +1.4 DU globally). According to the model results, the
resulting ultraviolet B (UVB) perturbation at the surface accounts for −4.3 % as a global and annual average
(versus −2.4 % in the SG-SO2 case), with a springtime Antarctic decrease of −2.7 % (versus a +5.8 % increase
in the SG-SO2 experiment). Overall, we find that an increase in COS emissions may be feasible and produce a
more latitudinally uniform forcing without the need for the deployment of stratospheric aircraft. However, our
assumption that the rate of COS uptake by soils and plants does not vary with increasing COS concentrations
will need to be investigated in future work, and more studies are needed on the prolonged exposure effects to
higher COS values in humans and ecosystems.

Full paper:

https://acp.copernicus.org/articles/22/5757/2022/

Best,

Ron

[Alan Robock ☮]

But it's nasty stuff.  Please keep in mind the last sentence of the abstract, "However, our assumption that the rate of COS uptake by soils and plants does not vary with increasing COS concentrations will need to be investigated in future work, and more studies are needed on the prolonged exposure effects to higher COS values in humans and ecosystems."

From the National Library of Medicine, https://pubchem.ncbi.nlm.nih.gov/compound/Carbonyl-sulfide :

"Carbonyl sulfide is a colorless, poisonous, flammable gas with a distinct sulfide odor. The gas is toxic and narcotic in low concentrations and presents a moderate fire hazard."

Alan

Alan Robock, Distinguished Professor
Department of Environmental Sciences      Phone: +1-848-932-5751
Rutgers University             E-mail: rob...@envsci.rutgers.edu
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[Jessica Gurevitch]

Dang! And it sounded so appealing!

Sent from my iPhone

On Jun 25, 2022, at 3:22 PM, Alan Robock ☮ <rob...@envsci.rutgers.edu> wrote:



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[Ron Baiman]

Thanks Alan.  Yes, more investigation on this is needed, as noted in my blurb as well.  I'm adding the lead author to this discussion in the event that she might be interested in participating in this discussion and is not in any of the lists.

Below is a snippet from the paper (p. 57580 that I think is relevant to your point.

Ron

"In quiescent volcanic conditions, COS is the main contributor
of sulfate aerosols in the Junge layer (Brühl et al., 2012),
where, after photodissociation by ultraviolet light and oxidation
processes, it is turned into SO2 and subsequently oxidized
into sulfuric acid, forming sulfate aerosols (Crutzen,
1976). It is naturally produced by various biological processes
and environments, such as saline ecosystems, rainwater
(Mu et al., 2004), and biomass burning. Furthermore, it is
also produced in various industrial processes (Lee and Brimblecombe,
2016) after CS2 is oxidized. Its chemical life is
very long (35 years; Brühl et al., 2012), and thus, its main
sink is the uptake from oxic soils (Kuhn and Kesselmeier,
2000; Steinbacher et al., 2004) and vegetation (Sandoval-
Soto et al., 2005). In the concentrations found in the atmosphere,
it is not a toxic gas for humans; negative effects
have not been found even at around 50 ppm (parts per
million), which is 100 000 times more than the background
mixing ratio, and for long exposure times in mice and rabbits
(Svoronos and Bruno, 2002). Higher concentrations than
that can, however, be harmful (Bartholomaeus and Haritos,
2006). Not much is known, however, about the response of
ecosystems in the presence of high concentrations of COS.
Stimler et al. (2010) showed that high levels of COS enhance
the stomatal conductance of some plants, which might
in turn have other unforeseen effects; furthermore, Conrad
and Meuser (2000) proposed that high COS concentrations
may interact with soils and possibly change soil pH. For the
reasons listed above, Crutzen (2006) discarded the idea of
using surface emissions of COS to increase the stratospheric
aerosol burden.
In this work, we use the University of L’Aquila Climate
Chemistry Model (ULAQ-CCM) to perform simulations to
verify if the increase in surface emissions of COS would be a
viable form of sulfate geoengineering, by obtaining a stratospheric
aerosol optical depth (AOD) similar to that obtained
with the injection of 8 TgSO2 in the stratosphere. We also
perform simulations where the release of COS is localized
in the tropical upper troposphere. This allows us to investigate
whether the increase in surface concentrations of COS
can be avoided, while, at the same time, circumventing the
need to reach altitudes that are currently unattainable with
modern aircraft (Smith et al., 2020). Together with assessing
the resulting aerosol cloud, we also explore the eventual side
effects on key chemical components in the atmosphere in order
to determine how the side effects from COS-induced sulfate geoengineering

compare with those from SO2-induced sulfate geoengineering."

[Michael MacCracken]

But it also does not have to be released at surface to be effective--release it from remote mountain tops or otherwise at elevated levels. Also, the study here was for a rather high loading--if the world would get busy on emissions reductions and the desired effect were to shave off peak warming, the concentrations would be lower. There is no perfect situation and the question is the relative tradeoffs for realistic applications. And if one could combine it with something less toxic that would only dissociate with high UV, the COS would end up primarily in the stratosphere. So, chemists need to keep searching.

Mike

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[Daniele Visioni]

We do have a study case in the paper where we inject in the upper troposphere rather than at the surface, for which the load necessary is much lower and the surface concentrations of COS result to be lower.

As Alan said, this still needs a lot of research in various fields (ecology especially), but it might have some potential overall if higher altitudes result to be unreachable.

On 26 Jun 2022, at 02:17, Michael MacCracken <mmac...@comcast.net> wrote:



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[Ron Baiman]

FYI, attached is the Chin and Davis 1993 paper on COS and CS2 sources and sinks referred to in the 2022 Quaglia et al paper.