Atmospheric Methane destruction: Tropospheric iron salt aerosol injection

Industry

Methane is a highly potent greenhouse gas and its reduction is given ever greater priority in international emission reduction policies. Given the increasing, and potentially catastrophic rate of methane release from the thawing Arctic and Northern permafrost, these regions are crucial in this endeavor. Apart from the methane release from microbial activity in thawing permafrost on land, methane also escapes in the form of hydrates which have been formed under sediments beneath the sea.

There are various methods to remove atmospheric methane. Tropospheric Iron Salt Aerosol injection (ISAI) has recently received significant attention as a potential methane mitigation technique. It would mimic a naturally occurring methane degrading process by injecting iron salts in the troposphere. In reaction with sunlight, these iron salts would irradiate and form chlorine radicals, which would then allow methane to be degraded into CO2. Alongside this methane destruction capability, ISAI is said to have other climate cooling effects as it might break down tropospheric ozone, and, if released over oceans, it might brighten clouds (see Arctic marine cloud brightening) and the iron particles might fertilize the ocean (see Ocean fertilization). Potentially, the aerosols could be distributed by ships.

Technological Readiness Level (TRL)

Low 1

The technology was patented in 2002, but only really highlighted to the broader scientific community in a 2017 paper by Oeste et al, and is at a very initial stage. Apart from institutional research (see: https://www.sparkclimate.org/methane-removal/grantees), there is significant private interest in the technology, with the MIT review finding at least 3 commercial companies experimenting with the technology (Temple, 2023). A main next step would be small-scale outdoor testing to provide clarity on the feasibility of this technology (Oeste and Elsworth, 2022), with Blue Dot Change for example planning the experimental release such aerosols from already sailing ocean going ships (https://www.bluedotchange.com/, see also Temple, 2023). Many scientific uncertainties still remain (Nisbet- Jones et al, 2021), and as not many studies have been published by scholars who have not been directly or indirectly involved in the research projects it is hard to evaluate the claims made in some of the papers.

Technological Readiness Level (TRL)

A technology with a TRL of 1-3: TRL 1 – Basic; TRL 2 – Concept formulated; TRL 3 – Experimental proof of concept

Scalability

High 3

This measure can likely be easily scaled up and deployed anywhere around the planet.

Scalability

High ability to scale physically; exponential efficiencies

Timeliness for near-future effects

Unknown 0

Although some grand claims exist around ISAI (see for example Oeste et al, 2017), and Ming et al (2021) claim it could be deployed relatively straightforwardly through modification of combustion fuels of the shipping industry, or major fossil fuel power plants, there are still many uncertainties about the actual feasibility of this measure.

Northern + Arctic potential

Unknown 0

Sun et al (2022) show early methane mitigation strategies are key to preserving Arctic summer sea ice. However, it is hard to evaluate the potential of this measure. ///

Global potential

Unknown 0

Given the potential impact of methane mitigation, the potential impact of this measure could be major. However, the current scientific status of the technology does not yet allow substantiated evaluations on the potential.

Cost - benefit

Medium 2

Ming et al. 2021 give a cost of ~$1/tCO2, which would make it by far the cheapest measure for CDR.

Cost - benefit

Significant investment costs needed, but still much cheaper than the avoided damage costs (e.g., 30%).

Environmental risks

Unknown 0

The technology is until now not explored, and possible effects unknown (Nisbet- Jones et al, 2021), with some scholars explicitly warning against it (see Temple, 2023). Ming et al, (2021) claim some of these fears, like the potential negative effect of iron fertilization on algae blooms, do not apply to ISAI because of the smaller amount of used aerosols in comparison to artificial fertilization proposals (see Artificial Fertilization), and Sturtz et al (2022) equally found that a hypothetical outdoor test would remain within safe levels.

Community impacts

Unknown 0

Ease of reversibility

Unknown 0

Risk of termination shock

Unknown 0

Legality/governance

Unknown 0

Nisbet- Jones et al (2021) warn that measures like these could become relevant over the coming years, and that political, governance, and ethical issues need to be taken into consideration. No governance focus studies on ISAI exist as of yet, but, depending on the magnitude of the potential listed effects, it is possible that deployment might be relevant to multiple governance regimes, for example related to marine pollution and SRM governance.

Scientific/media attention

Medium 2

Attention for methane action has been increasing (see for example advocacy group Methane Action methaneaction.org and O'Grady, 2021), especially in the wake of the Global Methane Pledge (https://www.globalmethanepledge.org/). Of the many suggested methane mitigation measures, ISAI is increasingly often found. However, the scope of scientific research is as of yet very limited, and commercial companies are relatively prominent in the research into it (Temple, 2023).

Scientific/media attention

Some attention within the scientific community, including published research and funding programmes; some media attention; some commercial interest

References

Jackson, R. B., Abernethy, S., Canadell, J. G., Cargnello, M., Davis, S. J., Féron, S., ... & Zickfeld, K. (2021). Atmospheric methane removal: a research agenda. Philosophical Transactions of the Royal Society A, 379(2210), 20200454. https://doi.org/10.1098/rsta.2020.0454

Kim, J., Maiti, A., Lin, L. C., Stolaroff, J. K., Smit, B., & Aines, R. D. (2013). New materials for methane capture from dilute and medium-concentration sources. Nature communications, 4(1), 1694. https://doi.org/10.1038/ncomms2697

Ming, T., Davies, P., Liu, W., & Caillol, S. (2017). Removal of non-CO2 greenhouse gases by large-scale atmospheric solar photocatalysis. Progress in Energy and Combustion Science, 60, 68-96. https://doi.org/10.1016/j.pecs.2017.01.001

Ming, T., de Richter, R., Oeste, F. D., Tulip, R., & Caillol, S. (2021). A nature-based negative emissions technology able to remove atmospheric methane and other greenhouse gases. Atmospheric Pollution Research, 12(5), 101035. https://doi.org/10.1016/j.apr.2021.02.017

Nisbet-Jones, P. B., Fernandez, J. M., Fisher, R. E., France, J. L., Lowry, D., Waltham, D. A., ... & Nisbet, E. G. (2022). Is the destruction or removal of atmospheric methane a worthwhile option?. Philosophical Transactions of the Royal Society A, 380(2215), 20210108. https://doi.org/10.1098/rsta.2021.0108

Oeste, Franz, and Clive Elsworth (2022), Essentials of the rich EDARA photochemistry, its albedo enhancement its impact on the ocean’s photic zone and the status of its development.

Sturtz, T. M., Jenkins, P. T., & de Richter, R. (2022). Environmental Impact Modeling for a Small-Scale Field Test of Methane Removal by Iron Salt Aerosols. Sustainability, 14(21), 14060. https://doi.org/10.3390/su142114060

Sun, T., Ocko, I. B., & Hamburg, S. P. (2022). The value of early methane mitigation in preserving Arctic summer sea ice. Environmental Research Letters, 17(4), 044001. https://doi.org/10.1088/1748-9326/ac4f10

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