Capturing Air Pollution: Innovative Methods To Purify The Atmosphere

The buildup of carbon dioxide in the atmosphere is a major contributor to climate change. Carbon capture and storage (CCS) is a technological concept that involves capturing carbon dioxide from power stations and industrial sources and storing it underground. Direct air capture (DAC) is a type of CCS that scrubs CO2 from the air and stores it underground or in long-lived products. DAC has the potential to create jobs and combat climate change, but it is currently costly and energy-intensive. Several organizations are investing in research to improve DAC technologies and make them more efficient and economically viable.

Direct air capture

DAC is different from carbon capture and storage (CCS), which captures emissions at the source, such as a power plant or industrial facility, and prevents them from entering the atmosphere. CCS involves capturing CO2 and burying it deep underground. While CCS may have an overall positive effect on air pollution, it can also increase emissions of some pollutants, such as NH3, NOx, and PM.

DAC technologies extract CO2 from the atmosphere at any location, and it can be stored in deep geological formations or used for various applications. The process of DAC involves chemically scrubbing CO2 from the air and then sequestering it either underground or in long-lived products like concrete. Scientists use two main approaches for DAC: liquid solvents and solid sorbents. Solvent-based DAC systems pass air through chemicals that remove the CO2, while sorbent-based systems use physical filters that chemically bind with CO2 molecules.

DAC has a critical role in helping to address legacy emissions and achieve a net-zero emissions future. However, one of the downsides of DAC is its current cost, as capturing CO2 from the air is the most expensive application of carbon capture. DAC requires a lot of power because only a tiny percentage of the atmosphere is made up of CO2, and there are also costs involved in storing or using the captured CO2. Despite this, DAC is a key approach needed to achieve net-zero emissions by 2050, and organizations like the Department of Energy (DOE) are working to bring down the costs of carbon removal technologies.

Carbon capture and storage (CCS)

CCS has been called a "proven technology" by the Global CCS Institute, which has been in safe operation for over 45 years. As of 2022, there were 194 large-scale CCS facilities globally, with a collective CO2 capture capacity of 244 million tonnes per annum. CCS facilities are mostly located in the Americas and Europe, with 80 in the US and 27 in the UK. CCS is considered to have an overall positive effect on air pollution and climate change, but it is important to note that emissions of certain pollutants, such as NH3, NOx, and PM, may increase due to the additional fuel consumption and extraction processes involved.

CCS is a form of emissions reduction rather than carbon removal, as it captures emissions at the source and prevents their release. However, there are other carbon removal strategies, such as growing trees or direct air capture (DAC), which chemically scrubs CO2 from the ambient air and sequesters it underground. While DAC is currently expensive and less efficient than capturing CO2 from industrial sources, it can be an effective way to remove excess carbon that has already been emitted into the atmosphere.

CCS is projected to play a central role in helping regions like Europe achieve their long-term GHG reduction objectives in a cost-effective manner. By complementing a broader shift to renewable energy, CCS can bridge the gap and cut emissions until a low-carbon economy can be realised.

Biomass carbon removal and storage (BiCRS)

BiCRS includes a range of processes that utilise biomass from plants or algae. One such process is the creation of biochar, which is produced by heating biomass in an environment with low oxygen to create a charcoal-like substance that can be added to soil. Biochar is a stable form of organic carbon that can sequester carbon and provide numerous benefits, including soil enrichment, water stabilisation, pollution management, waste treatment, and even potential applications in steel production. Another method is the production of bio-oil, which uses a similar process to create a liquid that can be injected underground. Additionally, carbon-rich biomass can be stored permanently in vaults.

Bioenergy Carbon Capture and Storage (BECCS) is another crucial carbon removal pathway within the BiCRS framework. BECCS involves burning biomass to generate energy while capturing and storing the resulting CO2 emissions. To achieve negative emissions, the amount of CO2 stored must exceed the CO2 emitted during biomass production, transport, conversion, and utilisation.

According to estimates, BiCRS strategies have the potential to capture and store 2.5-5.5 gigatons of CO2 annually by the middle of the century. However, challenges to scalability exist, including the availability of sustainable and contaminant-free feedstocks and the capital and operational costs of biomass conversion plants. Nonetheless, BiCRS offers a promising approach to carbon removal and storage, contributing to the global efforts to mitigate climate change and reduce air pollution.

Using CO2 to create valuable products

Carbon capture and storage (CCS) is a method of capturing carbon dioxide released by power stations and industrial sources and burying it deep underground. While this method keeps a significant greenhouse gas out of the atmosphere, it does not make use of the captured CO2 to create valuable products.

Direct air capture is a similar technology that scrubs CO2 from the air and sequesters it underground or in long-lived products like concrete. This method removes excess carbon that is already in the atmosphere, but it is costly and energy-intensive.

One way to incentivize the capture of CO2 is to identify valuable products that can be made from it. Researchers at Stanford and SLAC are working on ways to convert waste carbon dioxide into chemical feedstocks and fuels through a process called electrochemical conversion. This process, when powered by renewable energy sources, could reduce carbon dioxide levels in the air and store energy from these sources in a form that can be used at any time.

Another way to create valuable products from CO2 is to use biological materials, including DNA, to convert it into valuable chemicals or fuels. This approach, explored by Professor Ariel Furst and colleagues at MIT, employs small-molecule catalysts to convert CO2 into carbon monoxide, which can then be used to make important molecules such as alcohols, fuels, and other valuable products.

Overall, using CO2 to create valuable products has the potential to become big business and provide a new incentive to reduce emissions. It could also help offset the cost of reducing emissions or removing carbon dioxide from the atmosphere.

CO2 as a fuel or fertiliser

Carbon dioxide removal aims to mitigate climate change by removing carbon dioxide pollution from the atmosphere. One way to do this is through carbon capture and storage (CCS), which captures emissions at their source, such as from power plants or industrial facilities, and prevents them from entering the atmosphere. Another method is direct air capture, which chemically scrubs carbon dioxide from the air and stores it underground or in long-lived products like concrete. While CCS and direct air capture can help reduce carbon dioxide in the atmosphere, they may also have trade-offs, potentially increasing emissions of certain pollutants such as ammonia, nitrogen oxide, and particulate matter.

To further combat climate change, we can explore ways to utilise captured CO2 and turn it into something valuable. One idea is to use CO2 as a fuel or fertiliser. While this approach can provide a short-term solution, it is not a long-term answer to climate change. This is because, when the CO2 fuel or fertiliser is used, the CO2 ends up back in the atmosphere. To be truly climate neutral, the CO2 feedstock must be sourced from the air, requiring a significant amount of renewable energy.

CO2 can act as a fertiliser by increasing the rate of photosynthesis in plants, leading to greater growth rates. Studies have shown that elevated CO2 levels can increase the yield of large-scale agricultural crops such as corn, wheat, and soybeans. Additionally, CO2 fertilisation can help plants withstand droughts and protect them against diseases. However, it is important to note that the use of synthetic fertilisers, especially nitrogen-based fertilisers, can contribute significantly to greenhouse gas emissions.

To address the challenges of using CO2 as a fuel or fertiliser, we must explore innovative solutions. For instance, biochar, a stable form of organic carbon derived from plant material through a process called pyrolysis, can be utilised. Biochar serves as a soil additive, enhancing carbon sequestration and improving soil health. Additionally, the implementation of the "Green" pathway, which involves using renewable fuels to replace natural gas-derived hydrogen, can create a need for bio-based CO2 in urea production, reducing emissions associated with fertiliser production.

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