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Atmospheric Methane Removal Approaches

Iron Salt Aerosols

Rising temperatures are increasing the risk of natural systems releasing methane, which would drive further warming. Existing efforts towards reducing anthropogenic greenhouse gas emissions and removing atmospheric carbon dioxide are crucial, but may be insufficient to maximally decrease the chance of, and then possible impact of, these risks. Atmospheric methane removal approaches are being researched to determine how to remove methane from the atmosphere faster than natural systems alone, in order to help lower peak temperatures and counteract some of the impacts of large-scale natural systems methane releases.

Atmospheric methane removal, should any approaches prove highly scalable, effective, and safe, could help address some of the current 0.5°C—and rising—of methane-driven warming. All proposed atmospheric methane removal approaches are at a very early stage today: some ideas have been proposed, some are being researched in laboratories, but none are yet ready for deployment. Spark believes that accelerating research to develop and assess which, if any, of these approaches might be possible and desirable is an important additional risk mitigation strategy.

A number of atmospheric methane removal approach ideas have been raised—including
Iron Salt Aerosols
, which is currently
Under investigation
, with major breakthrough innovations required to change this
This approach, based on early analysis, will likely require multiple breakthroughs in order to feasibly address atmospheric methane levels. It may hold the most promise if it also delivers separate benefits (e.g. for climate or pollution), as part of systems deployed for other primary reasons, or to address low-concentration methane sources.

Iron Salt Aerosols


Iron salt aerosols (ISA) involves lofting iron-based particles into the atmosphere (e.g., from ships or towers) to enhance atmospheric chlorine radicals, a natural methane sink. This method mimics a natural phenomenon that is currently being studied to characterize its methane oxidizing impact. In contrast to some of the other methods, this approach is catalytic; the iron uses sunlight to convert abundant chloride (e.g. from sea spray) into reactive chlorine. It may prove feasible, but much more scientific study would be needed to understand the full set of impacts, including risks and side effects, before this can be determined.

Several entities have formed to commercialize ISA. Some propose to sell methane credits for ISA deployment. Given the early stage of the research, this is premature. Any approach to oxidizing additional methane in the atmosphere that involves altering atmospheric chemistry needs to be well understood prior to any deployment. Independent scientific analysis and social acceptance are prerequisites.


Learn more about how we evaluate cost plausibility and climate impacts

While more research is needed to fully assess the approach, ISA is potentially climate beneficial and cost-plausible.

The natural occurrence of iron in mineral dusts is believed to generate chlorine radicals via a natural analogue of the ISA mechanism. This effect is believed to be catalytic, with each iron molecule having the potential to produce multiple chlorine radicals before deposition. This catalytic effect is poorly understood and highly dependent on local conditions, yielding anywhere between zero and tens of chlorine radicals per iron molecule. 

The potential release of iron would have impacts beyond only breaking down methane.  Iron salts themselves have unknown side effects on warming, cloud formation, deposition products, and other Earth system impacts. The produced chlorine radicals would also break down tropospheric ozone, which has mixed effects depending on atmospheric conditions. Decreased tropospheric ozone is beneficial because ozone is a powerful greenhouse gas and an air pollutant. However, photolysis of ozone is the primary source of hydroxyl radicals (OH) which remove methane. This suppression of hydroxyl radicals could paradoxically lead to a longer methane lifetime in certain atmospheric conditions.  It is important to note that the efficiency of the process will be limited by factors such as the percentage of photoactive iron in the emitted iron, the reaction of chlorine radicals with atmospheric species other than methane, and the rate at which the iron salt chloride can regenerate its reactive form.The cost of implementing ISA is not yet known. There are many uncertainties regarding ISA’s efficacy and efficiency in producing chlorine radicals, its effect on net oxidative capacity, and overall impact on warming. Until they’re resolved we can’t know how much additional methane ISA could oxidize and how much it might cost per ton of methane broken down or unit of warming avoided. Costs and performance will also vary according to factors such as ISA particle size, deployment strategy, and atmospheric conditions where the reaction is taking place. However, preliminary estimates suggest that it could be cost-plausible given its catalytic nature.


Learn more about how we evaluate scalability

The potential scale for iron salt aerosols would be primarily determined by atmospheric dynamics,  the socially acceptable concentrations of these aerosols, raw material constraints associated with their production, and the amount of chlorine available in the atmosphere. 

We estimate that scaling to 10 million metric tons of methane (830 Mt CO2e using GWP20), a benchmark for scale, could occur within a decade after an initial hypothetical first successful methane megaton scale deployment. Given the many potential impacts of ISA beyond only methane breakdown, analyses of scale and cost need to look at the full climate and environmental effects, beyond only possible atmospheric methane reduction.

Health & Environmental Considerations

Given the very early state of the science behind ISA, the tradeoffs between its potential health and environmental co-benefits and its potential negative impacts are not yet well understood. It’s therefore critical to thoroughly study them before contemplating deployment.

It is not yet known whether ISA might have harmful side effects on the climate or the environment. The ISA photochemistry shifts chlorine between different forms, which could potentially change the acidity of atmospheric aerosols or even areas of the ocean and it could also potentially produce byproducts. 

Airborne iron particles may contribute to particulate pollution which may have potential human health impacts on individuals at the deployment site or downstream. The iron would eventually settle out of the atmosphere, landing on water, land, or ice. This may have potentially beneficial or harmful effects. Iron could fertilize bacterial growth on ice, reducing albedo and increasing melting; in the ocean it could fertilize algal growth, potentially sequestering carbon and/or cause algal blooms that could negatively affect marine habitats. It’s also possible that harmful chlorinated compounds in gaseous, liquid, or solid form could be produced.

Learn More

State of Research
Thank you to
Matthew Johnson (University of Copenhagen)
for their contributions to, and review of, this content.
This is a living document — we welcome suggested updates here or by contacting us.

Explore Other Potential Approaches

Approaches Overview

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