Direct Air Capture and Activated Carbon for UPSC: Full Notes on CO2 Removal, Pollutant Adsorption and Indian Industry

UPSC notes on Direct Air Capture and activated carbon: working, world plants (Climeworks Mammoth, Stratos), India pilots, physisorption vs chemisorption, costs, MCQs and FAQs.

India’s UPSC 2025 Prelims paper put two adsorption-based environmental technologies on the same answer sheet — activated carbon in Question 10, Direct Air Capture in Question 16. Both rely on the same fundamental physics, both sit at the heart of pollution control and climate policy, and both are increasingly tied to India’s industrial future. This note pulls them together into a single revision document, written for candidates who want to understand the underlying science as well as the policy, plant data, and Indian linkages that turn a fact into a usable Mains argument. ## What Direct Air Capture Actually Does Direct Air Capture is the engineering of removing carbon dioxide directly from the open atmosphere rather than from the concentrated flue gas of a power plant or cement kiln. The distinction matters more than it sounds. Ambient air contains only about 420 parts per million of CO2 — that is 0.042% by volume. Flue gas from a coal plant carries 10–15%. The two technologies share a name (carbon capture) but solve very different physical problems. Point-source capture is a refinement problem — you already have a CO2-rich stream and you separate it. DAC is a concentration problem — you must move enormous volumes of air across a sorbent to gather the same tonne of CO2. A rough benchmark: a DAC plant capturing one million tonnes per year needs to process roughly the air volume that flows over a town of 100,000 people in a day. That single fact dictates everything that follows — the energy footprint, the cost, the siting logic, and the placement of DAC in IPCC modelling. ## Working Principle — Sorbent Chemistry in Two Families Every operating DAC system uses a sorbent that selectively binds CO2 from passing air and then releases it under heat or pressure for capture. Two chemistries dominate the industry. Liquid-solvent DAC uses strong alkaline solutions — typically potassium hydroxide (KOH) or sodium hydroxide (NaOH). Air is drawn through large contactor walls where CO2 reacts with hydroxide ions to form carbonate. The carbonate solution is then processed through a pellet reactor with calcium hydroxide to form calcium carbonate, which is calcined at around 900 °C to release pure CO2 and regenerate the calcium oxide. Carbon Engineering, the Canadian-American firm now owned by Occidental, pioneered this route and uses it in the Stratos plant in Texas. Solid-sorbent DAC uses amine-functionalised porous materials — typically polyamines grafted onto silica, metal-organic frameworks, or cellulose fibres. Fans draw air through filter modules where CO2 is chemically bound to the amine groups. When the filter saturates, the module is sealed and heated to 80–120 °C, often under vacuum, releasing concentrated CO2. Climeworks uses this approach in Orca and Mammoth in Iceland; its modular design lets capacity be added one container at a time. The trade-off between the two families maps neatly onto a comparison:

Parameter	Liquid-solvent DAC	Solid-sorbent DAC
Sorbent	KOH/NaOH aqueous solution	Amine-functionalised porous solid
Regeneration temperature	~900 °C (calcination)	80–120 °C + vacuum
Energy form needed	High-temperature heat (gas/electric)	Low-grade heat (geothermal, waste heat)
Footprint	Very large contactor walls	Modular containerised units
Water use	1–7 t water per t CO2	Lower; can release water
Best paired with	Natural gas + CCS, geothermal	Geothermal, low-grade renewables
Leading firm	Carbon Engineering / 1PointFive	Climeworks, Global Thermostat
Marquee plant	Stratos (Texas, 500,000 tpa)	Mammoth (Iceland, 36,000 tpa)

The thermodynamic floor for separating CO2 from ambient air is about 0.5 GJ per tonne. Real plants spend 6–10 GJ per tonne. The gap is the engineering challenge of the next decade. A third, less mature family is electrochemical DAC — driving CO2 capture and release through pH swings or redox-active sorbents powered by electricity rather than heat. MIT, Verdox, and RepAir are the visible names. The attraction is direct compatibility with intermittent renewables (no thermal storage needed), but the technology is at single-tonne pilot scale and a decade behind the chemical routes. The siting logic of DAC also differs from point-source capture. Because CO2 concentration is the same everywhere on Earth (within 5–10 ppm), DAC plants can be placed wherever clean energy is cheapest and storage geology is closest — not where the emitter sits. This is why Iceland, Wyoming, Texas, and the Persian Gulf dominate the project map: each combines abundant clean or stranded energy with proven storage geology. ## The World’s DAC Plants — Where the Tonnes Actually Are For all the policy hype, operating capacity worldwide is tiny. As of mid-2026, total commissioned DAC capacity is around 50,000 tonnes per year — about the annual emissions of 10,000 average Indian cars. The IEA estimates capacity needs to reach 70 million tonnes per year by 2030 and several billion tonnes by 2050 to align with 1.5 °C pathways.

Plant	Location	Operator	Capacity (t CO2/yr)	Status	Storage method
Mammoth	Hellisheidi, Iceland	Climeworks	36,000	Operating (May 2024)	CarbFix basalt mineralisation
Orca	Hellisheidi, Iceland	Climeworks	4,000	Operating (2021)	CarbFix basalt mineralisation
Stratos	Ector County, Texas	1PointFive / Occidental	500,000	Commissioning 2025–26	Saline aquifer + CO2-EOR
Project Bison	Wyoming, USA	CarbonCapture Inc.	5,000 (Phase 1)	Construction	Geological storage
South Texas DAC Hub	Kleberg County, Texas	1PointFive (DOE-funded)	1,000,000+	Planning	Saline aquifer
Cypress DAC Hub	Louisiana, USA	Battelle (DOE-funded)	1,000,000+	Planning	Saline aquifer
Hunt 1 (NEOM)	Saudi Arabia	Aramco / 44.01	~1,250	Pilot	Peridotite mineralisation
Heirloom Tracy	California, USA	Heirloom Carbon	1,000	Operating (2023)	Concrete mineralisation

Two patterns stand out. First, the United States dominates the project pipeline because of the 45Q tax credit and the DOE’s USD 3.5 billion Regional DAC Hubs programme funded under the 2021 Bipartisan Infrastructure Law. Second, Iceland dominates operating capacity because cheap geothermal electricity and an abundance of young basalt rock make it the perfect natural laboratory. ## India’s DAC Position — Pilots, Not Plants India has no commercial DAC plant. What it has is a constellation of research pilots and an enormous latent advantage in basalt geology that the policy conversation has barely begun to use. NTPC’s research wing NETRA at Greater Noida is running small-scale DAC trials using solid amine sorbents, and a 20-tonne-per-day amine-based post-combustion capture pilot at the Vindhyachal coal plant in Madhya Pradesh converts captured CO2 to methanol. BHEL has begun engineering studies for indigenous absorber–stripper columns. IIT Bombay leads a multi-institutional consortium under the DST National Carbon Capture, Utilisation and Storage mission exploring solid sorbents and basalt mineralisation, with field studies in the Deccan Volcanic Province. ONGC has piloted CO2-enhanced oil recovery in the Gandhar field in Gujarat. The most under-discussed Indian asset is the Deccan Traps. The Deccan basalts cover roughly 500,000 km² across Maharashtra, Gujarat, Madhya Pradesh, and Karnataka and reach depths of 2,000 metres in places. Globally, basalt mineralisation through the CarbFix process has been shown to convert injected CO2 into solid carbonate within two years. Indian estimates place the Deccan’s theoretical mineralisation capacity at over 100 billion tonnes of CO2 — more than two centuries of India’s current emissions. Whether this gets commercialised is a function of policy, not geology. ## Carbon Storage — Where the CO2 Actually Goes Capturing CO2 is half the problem. Storing it permanently is the other half. The IPCC recognises four main categories of geological storage and several routes for utilisation.

Storage option	Mechanism	Permanence	Global capacity (Gt)	Indian potential
Deep saline aquifers	Solubility + structural trapping	1,000+ years (likely)	5,000–25,000	~290 Gt (CGS estimate)
Depleted oil & gas fields	Re-injection into proven seal	1,000+ years	675–900	~7 Gt (ONGC estimate)
Basalt mineralisation	Reaction to form carbonate rock	Permanent (geological)	100,000+ theoretical	~100 Gt (Deccan Traps)
Unmineable coal seams	Adsorption on coal matrix	Variable	3–200	Indian coalfields under study
CO2-EOR (utilisation)	Pressurise old oil reservoirs	Co-benefit storage	Limited	ONGC Gandhar pilot
Concrete mineralisation	React CO2 with cement	Permanent	Scale-limited	Pilot stage

The CarbFix project in Iceland deserves a paragraph of its own because it is the only mineralisation pathway with multi-year operational data. CarbFix dissolves CO2 in water and injects the carbonated water into basalt at 400–800 m depth. The CO2 reacts with calcium, magnesium, and iron in the rock to form carbonate minerals — the same chemistry that produces limestone, only thousands of times faster. Isotopic tracing has shown over 95% mineralisation within two years at the Hellisheidi site. The cost is currently around USD 25 per tonne for the injection step alone, which is competitive once paired with cheap clean power. ## Cost Economics and the Policy Levers DAC is expensive. Current full-cost estimates from operators and independent analysts cluster between USD 400 and USD 1,000 per tonne of CO2 removed. The IPCC’s Sixth Assessment Report and the IEA’s Net Zero Roadmap consider USD 100–200 per tonne the threshold for climate-relevant deployment. Three levers are pulling costs down. First, learning by doing. Climeworks claims a roughly 50% cost reduction from Orca (2021) to Mammoth (2024) and targets USD 300 per tonne by 2030 and below USD 200 by 2040. Second, the US 45Q tax credit was increased under the 2022 Inflation Reduction Act to USD 180 per tonne of CO2 captured via DAC and stored geologically, and USD 130 per tonne for CO2 used industrially. This single policy shifted the global DAC pipeline overwhelmingly to the United States. Third, the EU’s Carbon Border Adjustment Mechanism (CBAM), in transitional phase from 2023 and fully operational in 2026, places a carbon price on imports of steel, aluminium, cement, fertilisers, electricity, and hydrogen, raising the implicit value of every avoided or removed tonne. The voluntary carbon market is the wildcard. High-quality DAC-with-storage credits currently sell to Microsoft, Stripe, Shopify, JPMorgan, and other Frontier coalition members for USD 500–1,500 per tonne. These offtake agreements have effectively financed the construction of every operating DAC plant. ## Limitations — Why DAC Cannot Be the Whole Answer Three constraints make DAC a complement to emissions reduction, not a substitute. Energy. Even at the thermodynamic efficiency frontier, removing one gigatonne of CO2 by DAC would require around 250 TWh of clean electricity — roughly 15% of India’s total power consumption in 2024. Scaling to the 10 gigatonnes per year that IPCC models eventually call for would consume more clean electricity than the entire current global solar fleet generates. Water. Liquid-solvent DAC consumes 1–7 tonnes of water per tonne of CO2 captured, with the high end approaching the water intensity of coal power. Solid-sorbent DAC in humid climates can in fact produce water as a co-product, but in arid deployments (the Saudi NEOM plant, planned Indian sites in Gujarat) water sourcing remains a non-trivial constraint. Scale gap. Current operating capacity worldwide is around 0.00001 of what 1.5 °C pathways require by 2050. Closing that gap requires capacity to grow by approximately 35% per year for two decades — faster than solar grew through the 2010s. Material throughput. A megatonne-per-year DAC plant processing ambient air at 420 ppm needs to move roughly 2.5 billion cubic metres of air annually — equivalent to a continuous airflow of 80,000 cubic metres per second. The fan, contactor, and sorbent material requirements grow linearly with capacity, which is one reason solid-sorbent DAC has favoured a modular containerised approach rather than ever-larger single units. Moral hazard. The fourth, non-physical limitation is political. Climate ethicists and the IPCC’s own framing warn that the presence of a hypothetical large-scale removal option can weaken the political appetite for emissions reductions in the present. Every IPCC pathway that uses heavy carbon removal in 2050 also assumes deep emissions cuts in 2030 — without the cuts, the removals cannot catch up. ## DAC in IPCC Pathways and the Net Zero Architecture The IPCC’s AR6 Working Group III report (2022) was unambiguous — every modelled pathway that limits warming to 1.5 °C requires both deep emissions reduction (around 43% below 2019 levels by 2030) and substantial carbon dioxide removal (CDR). CDR in IPCC scenarios includes afforestation and reforestation, soil carbon sequestration, bioenergy with carbon capture and storage (BECCS), DAC with storage (DACCS), ocean alkalinity enhancement, and enhanced mineral weathering. Median modelled CDR by 2050 across 1.5 °C scenarios is roughly 5–10 Gt CO2 per year, of which engineered removals (DACCS + BECCS) account for 1–8 Gt. The architecture matters for India because the Paris Agreement’s Article 6 establishes the rules for international carbon markets. Article 6.2 allows bilateral trading of internationally transferred mitigation outcomes (ITMOs), and Article 6.4 creates a centralised UN-supervised mechanism. India submitted its updated NDC in August 2022 with a 45% emissions-intensity reduction target by 2030, and the Long-Term Low Carbon Development Strategy filed at COP27 acknowledges carbon removal as part of the toolkit. Whether engineered DAC counts toward India’s NDC depends on the methodologies the Article 6.4 Supervisory Body finalises through 2026–27. ## Comparing DAC With Other Carbon Removal Routes

Method	Cost (USD/t CO2)	Permanence	Land needed	Scalability	Co-benefits
Afforestation/reforestation	5–50	Decades (reversible)	Very high	0.5–3 Gt/yr	Biodiversity, soil, livelihoods
Soil carbon sequestration	0–100	Decades (reversible)	Existing farmland	2–5 Gt/yr	Soil fertility, yields
Biochar	30–120	Centuries	Moderate	0.3–2 Gt/yr	Soil amendment
BECCS	100–200	Permanent if stored	Very high (cropland)	0.5–5 Gt/yr	Power, biofuel
DACCS	400–1,000 (today)	Permanent if stored	Low	Engineering-limited	None
Enhanced weathering	50–200	Permanent	Cropland	2–4 Gt/yr	Soil pH, micronutrients
Ocean alkalinity enhancement	40–260	Centuries to permanent	Ocean	1–15 Gt/yr (theoretical)	Reduced ocean acidification

The honest reading of this table is that DAC is the most expensive option per tonne but also the most land-light, the most measurable, and the only one whose output (a stream of concentrated CO2) can be quantified to the gram. Nature-based solutions are cheaper and offer co-benefits but suffer from reversibility (a forest fire releases stored carbon) and measurement uncertainty. A serious removal portfolio in 2050 will combine all of them. ## Part Two — Activated Carbon The science that underlies DAC sorbents — selective adsorption on engineered surfaces — is the same science that has underpinned air and water purification for more than a century. Activated carbon is the workhorse adsorbent of the modern world, used in everything from gas masks to insulin manufacture, and its physics is exactly what UPSC 2025 Q10 tested. ## What Activated Carbon Is Activated carbon is a form of carbon processed to have an extraordinarily high internal surface area arising from a dense network of submicroscopic pores. Commercial grades offer BET surface areas of 500–1,500 m² per gram, with high-performance varieties (KOH-activated coconut shell, certain MOF-derived carbons) reaching 3,000 m² per gram. The mental image to keep — a teaspoon of high-grade activated carbon has roughly the internal surface area of a football field. This surface is what does the work. Adsorption is a surface phenomenon, and the rate and capacity of any adsorbent scale directly with accessible surface area. The pore-size distribution decides which molecules can reach that surface.

Pore class (IUPAC)	Width	What it captures	Mechanism
Micropores	< 2 nm	Small gases (CO2, VOCs, chlorine)	Pore-filling, strong adsorption
Mesopores	2–50 nm	Larger organics (dyes, pesticides, humic acids)	Multilayer adsorption + capillary condensation
Macropores	> 50 nm	Transport channels (not adsorption sites)	Diffusion pathway to interior

Coconut-shell carbon is overwhelmingly microporous, which is why it dominates gas-phase and water-polishing applications. Wood-based and chemically activated carbons are richer in mesopores and dominate decolourisation, sugar refining, and dye removal. ## Production — Physical vs Chemical Activation The manufacturing route shapes the final pore structure, hardness, and ash content. Physical activation is a two-step process. The carbonaceous precursor (coconut shell, hardwood, lignite, bituminous coal, peat) is first pyrolysed at 600–900 °C in the absence of oxygen, driving off volatiles and leaving a char. The char is then activated at 800–1,000 °C in steam or CO2, which partially gasifies the carbon and opens up the pore network. Reactions are endothermic and slow, but the product is clean, ash-low, and dominantly microporous. This is the standard route for coconut-shell activated carbon and is the route Indian Kerala and Tamil Nadu plants use. Chemical activation impregnates the raw precursor with a dehydrating agent — zinc chloride (ZnCl2), phosphoric acid (H3PO4), or potassium hydroxide (KOH) — before a single-step thermal treatment at 450–700 °C. The chemical promotes dehydration and aromatisation, producing carbons with higher mesoporosity and often higher BET surface area. H3PO4 dominates wood-based AC for water treatment; KOH produces ultra-high surface area carbons for capacitors and gas storage. The disadvantage is the need to wash out residual chemicals and treat the wastewater. ## Adsorption Mechanism — Physisorption Versus Chemisorption This is the heart of UPSC 2025 Q10. The question framed activated carbon’s pollutant-removal capability as Assertion (I) and “adsorption is a phenomenon of physisorption” as Reason (II) and asked whether II explains I. The accepted answer is (a) — both true, II is the correct explanation. The mechanism on activated carbon is dominated by physisorption — adsorption driven by weak intermolecular forces (London dispersion, dipole–dipole, induction) between the carbon surface and the adsorbate. The key features:

Property	Physisorption	Chemisorption
Force type	van der Waals (London, dipole)	Chemical bond (covalent/ionic)
Enthalpy of adsorption	20–40 kJ/mol	80–400 kJ/mol
Reversibility	Easily reversible	Often irreversible
Specificity	Non-specific (any adsorbent + any gas)	Highly specific (matches surface chemistry)
Layer formation	Multilayer at higher P	Monolayer only
Temperature dependence	Decreases with T	Increases up to optimum, then decreases
Activation energy	Negligible	Significant (chemical reaction barrier)
Example	N2 on charcoal, organics on activated carbon	H2 on Ni, O2 on tungsten

The reason activated carbon works as a near-universal pollutant adsorbent is precisely because its adsorption is non-specific physisorption — anything that fits in the pores and has any polarisability gets stuck. Chemisorption, by contrast, would limit it to only those molecules with matching surface chemistry. The trade-off is that physisorption is reversible — saturated activated carbon can be regenerated by heating or steam stripping, which is also why DAC sorbents using amines (which are chemisorbents) need higher regeneration temperatures than purely physisorbent carbons. ## Applications — Where Activated Carbon Actually Earns Its Keep

Sector	Application	What it removes	India relevance
Drinking water	Granular AC filters	Chlorine, taste, odour, organics, trihalomethanes	Jal Jeevan Mission RO+AC modules
Industrial wastewater	Powdered AC dosing	Phenols, dyes, pesticides, pharmaceutical residues	CPCB-mandated polishing in pharma, textile
Air purification	AC cloth, canister filters	VOCs, SO2, mercury vapour	Industrial respirators, indoor air units
Military / first responder	Gas-mask cartridges	Chemical warfare agents, smoke	OFB, DRDO supply lines
Gold mining	CIP/CIL extraction	Gold cyanide complexes from leach slurry	Hutti Gold Mines (Karnataka)
Sugar refining	Decolourisation	Coloured organics, ash	Indian sugar mills (UP, Maharashtra)
Edible oil refining	Bleaching	Pigments, FFAs, oxidation products	Edible-oil refiners
Medical	Activated charcoal oral dose	Drug/toxin overdose	Standard ER protocol
Medical	Hemoperfusion cartridges	Uraemic toxins, drug overdose	Dialysis units
Food & beverage	Polishing of spirits, juices	Off-flavours, colour	Beverage industry
Automotive	Cabin air filters, evap canisters	VOCs, fuel vapours	BS-VI compliance kits
Energy storage	Supercapacitor electrodes	(Charge storage, not adsorption)	Research stage in India

The deepest historical hook is the gas mask. The first practical respirators issued to Allied troops after the German chlorine attack at Ypres in April 1915 used activated charcoal from coconut shell — the same feedstock India dominates today. Coconut-shell carbon was chosen because its high microporosity and hardness gave the best resistance to chlorine, phosgene, and mustard agents. That use case is what put activated carbon on the industrial map. ## India’s Activated Carbon Industry India is one of the world’s largest producers and exporters of coconut-shell activated carbon. The industry is concentrated in Kerala (Kollam, Ernakulam, Kottayam districts), Tamil Nadu (Pollachi, Coimbatore, Tirupur), and Karnataka, drawing on the southern Indian coconut belt for shell feedstock. Major Indian producers include Indo German Carbons (Kochi), Kalpaka Chemicals, Active Char Products, and Carbon Activated Corporation’s Indian operations. Estimated domestic production is around 100,000 tonnes per year, with a sizeable share exported to the United States, the EU, Japan, and increasingly South Korea for water treatment and air purification. The strategic vulnerability is that India imports coal-based activated carbon (used in flue-gas mercury control and certain industrial applications) from China and Sri Lanka. The opportunity is biomass-derived AC from rice husk, bagasse, bamboo, and palm kernel shell — feedstocks India has in abundance and which CSIR-NEERI and IIT laboratories are actively researching. Three innovation fronts are reshaping the activated-carbon industry. First, regeneration. Conventional thermal regeneration at 800 °C destroys 5–15% of the carbon per cycle and is energy-intensive. Steam regeneration at 200–400 °C, microwave-assisted regeneration, and in-situ biological regeneration (where biofilms degrade adsorbed organics on the carbon surface) all extend service life and cut operating cost. Second, hybrid systems — pairing activated carbon with membrane filtration, advanced oxidation, or UV produces compact tertiary treatment trains for difficult contaminants such as PFAS and pharmaceutical residues, both of which are emerging concerns in Indian wastewater. Third, functionalisation — surface modification with iron oxides, silver nanoparticles, or amine groups extends activated carbon’s reach into arsenic removal, antimicrobial action, and CO2 capture, blurring the line between the activated carbon of Part Two and the DAC sorbents of Part One. ## Comparing Activated Carbon With Other Adsorbents

Adsorbent	Surface area (m²/g)	Pore character	Strength	Weakness	Typical use
Activated carbon	500–3,000	Micro + meso	Universal, cheap, regenerable	Burns above 400 °C; weak for polar small molecules	Water, air, gold, medicine
Zeolites (synthetic)	300–800	Crystalline micropores	Molecular sieving, high selectivity, thermal stability	Expensive, deactivated by moisture	Petrochemicals, gas separation
Silica gel	300–800	Mesoporous	Excellent for water vapour	Low capacity for organics	Desiccant, drying
Activated alumina	200–400	Mesoporous	Fluoride, arsenic removal	Lower surface area	Drinking water defluoridation
Metal-organic frameworks	2,000–7,000	Designed micropores	Tunable, ultra-high capacity	Cost, stability under humidity	R&D for DAC, gas storage
Biochar	10–400	Variable	Soil amendment co-benefit, cheap	Lower performance per gram	Agriculture, low-grade water

The reason activated carbon remains dominant despite the technical superiority of zeolites and MOFs is cost. A tonne of granular activated carbon costs USD 1,500–3,500. A tonne of synthetic zeolite costs USD 3,000–10,000. A tonne of MOF currently costs USD 50,000–500,000. Where regulatory standards permit and adsorption capacity is adequate, activated carbon wins on price. ## Part Three — Policy and the Net Zero Architecture Both DAC and activated carbon sit inside India’s broader climate and pollution policy. The threads to pull for Mains answers: Net Zero by 2070 requires both deep emissions cuts and removals. The Long-Term Low Carbon Development Strategy (LT-LEDS) submitted at COP27 in November 2022 names afforestation under the Green India Mission, BECCS, and engineered removals as the removal toolkit. The 2024 update of the National Action Plan on Climate Change adds explicit reference to carbon capture, utilisation, and storage (CCUS) under the missions framework. The clean-power flywheel. DAC’s economics depend entirely on cheap, abundant, zero-carbon power. India’s PM Surya Ghar Muft Bijli Yojana (rooftop solar for 1 crore households, launched February 2024), the 50 GW renewable additions targeted annually under the bid trajectory announced by MNRE in 2023, the National Green Hydrogen Mission (4.5 lakh crore investment, 5 MMT hydrogen by 2030), and the Battery Energy Storage Systems (BESS) viability gap funding scheme (Rs 3,760 crore for 4 GWh storage) together build the conditions under which Indian DAC becomes thinkable in the 2030s. Article 6 and carbon markets. The Indian Carbon Credit Trading Scheme (CCTS) notified in June 2023 sets up a domestic compliance market with a perform-achieve-trade backbone inherited from PAT. Once Article 6.4 methodologies for engineered removals are finalised (expected 2026–27), Indian DAC projects could in principle issue ITMOs sellable to first-movers like Switzerland, Japan, and Singapore that are already buying removals to meet NDCs. CBAM exposure. The EU’s CBAM, transitional from October 2023 and operational from 2026, will price the embedded carbon in Indian steel, aluminium, cement, fertilisers, electricity, and hydrogen at the EU ETS price (currently EUR 60–90 per tonne). For the affected exporters (Tata Steel, JSW, Hindalco, ACC, Ambuja, GAIL) the cheapest abatement is process redesign, but DAC and CCS become commercially relevant as a residual-emission solution. Activated carbon and Swachh Bharat. Beyond climate, activated carbon’s domestic load is in the water-quality programmes. Jal Jeevan Mission’s RO+AC point-of-use modules, CPCB’s revised effluent norms for pharmaceutical and textile clusters mandating tertiary polishing, and the Namami Gange interventions all rely on activated-carbon-based units. The market growth here is steady and policy-driven. ## Global Carbon-Removal Market — Where the Money Is Flowing The voluntary carbon-removal market reached approximately USD 1.7 billion in transaction value in 2024 by Trove Research and Sylvera estimates, with engineered removals (DACCS, BECCS, biochar, mineralisation) accounting for the bulk of high-quality-credit revenue. The Frontier coalition (Stripe, Alphabet, Meta, Shopify, McKinsey Sustainability, and partners) has committed USD 1 billion to advance market commitments through 2030. Microsoft alone signed contracts in 2024 to purchase over 8 million tonnes of removal credits across DACCS, BECCS, biochar, and reforestation. JPMorgan, BCG, and the Klarna foundation have all signed multi-year DAC offtakes. For India, the relevant signal is that the international demand for permanent, measurable, high-quality removals is willing to pay USD 200–1,500 per tonne today. If Indian projects can demonstrate Article 6-compliant methodologies and use the Deccan basalts for permanent mineralisation, the export economics could close even before domestic carbon prices justify the spend. A comparative snapshot of India’s carbon-removal landscape against global benchmarks puts the gap and the opportunity in one frame.

Dimension	India today	Global frontier	India 2035 plausible
Operating DAC capacity	0 commercial; pilots only	~50,000 t/yr (Iceland, US)	10,000–100,000 t/yr (pilots scaled)
Storage capacity assessed	~290 Gt theoretical (CGS)	~25,000 Gt global	10–20 Gt characterised & permitted
Policy instrument	CCTS notified 2023; CCUS in LT-LEDS	US 45Q ($180/t), EU CBAM, UK CCUS clusters	Article 6 export contracts + CCTS removal credits
Lead institutions	NTPC NETRA, BHEL, ONGC, IIT-B, CSIR-NEERI	Climeworks, Carbon Engineering, CarbFix	NTPC/ONGC commercial-scale joint ventures
Mineralisation geology	Deccan basalts (under-tapped)	Hellisheidi basalts (proven via CarbFix)	Deccan pilot at >10,000 t/yr

## Practice MCQs — UPSC Pattern Q1. Consider the following statements regarding Direct Air Capture (DAC): 1. DAC captures carbon dioxide from concentrated industrial flue gas. 2. The Climeworks Mammoth plant in Iceland is the world’s largest operating DAC facility. 3. Captured CO2 can be permanently stored by mineralisation in basalt rock. Which of the statements given above are correct? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3 Answer: (b). DAC captures CO2 from ambient air, not concentrated flue gas — that is point-source capture. Q2. With reference to activated carbon, consider the following statements: 1. Activated carbon has a BET surface area typically between 500 and 3,000 m² per gram. 2. Adsorption on activated carbon is primarily a chemisorption process. 3. Coconut-shell activated carbon is rich in micropores. Which of the above are correct? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) All three Answer: (c). Adsorption on activated carbon is principally physisorption (van der Waals). Q3. Assertion (A): Direct Air Capture is energy-intensive compared with point-source carbon capture. Reason (R): The concentration of CO2 in ambient air (around 420 ppm) is far lower than in flue gases of fossil-fuel power plants. (a) Both A and R are true and R is the correct explanation of A (b) Both A and R are true but R is not the correct explanation of A (c) A is true but R is false (d) A is false but R is true Answer: (a). Q4. Which of the following are recognised carbon-storage routes after CO2 capture? 1. Deep saline aquifers 2. Depleted oil and gas reservoirs 3. Mineralisation in basalt formations 4. Concrete curing and mineralisation Select the correct answer: (a) 1 and 2 only (b) 1, 2 and 3 only (c) 2, 3 and 4 only (d) 1, 2, 3 and 4 Answer: (d). Q5. The CarbFix project, often discussed in the context of climate technology, is associated with: (a) Algal biofuel production (b) Mineralisation of CO2 into carbonate rock in basalt formations (c) Bioenergy with carbon capture and storage (d) Floating solar power plants Answer: (b). Q6. Consider the following pairs regarding adsorbents and their typical use: 1. Activated alumina — defluoridation of drinking water 2. Zeolite — molecular sieving in petrochemicals 3. Silica gel — desiccant 4. Activated carbon — removal of chlorine and taste from water How many of the above pairs are correctly matched? (a) Only two (b) Only three (c) All four (d) Only one Answer: (c). Q7. Which of the following statements about India’s carbon-capture landscape is/are correct? 1. NTPC has explored DAC pilots at its NETRA research wing. 2. The Deccan basalt province offers significant potential for mineralisation-based CO2 storage. 3. India has multiple commercial-scale DAC plants in operation. (a) 1 and 2 only (b) 2 and 3 only (c) 1 only (d) 1, 2 and 3 Answer: (a). India has no commercial-scale DAC plant yet. ## How To Use This Note In Mains For GS Paper-III (Environment and Science & Tech) and Essay, the workable framing is to treat DAC and activated carbon as two ends of a continuum — one ancient (charcoal water filters predate Roman aqueducts), the other still being invented, but both built on the same surface-adsorption physics. The argumentative move that scores in Mains is to acknowledge that DAC is not a substitute for emissions reduction — it is an insurance layer for residual emissions in hard-to-abate sectors and a way to address legacy CO2 already in the atmosphere. The Indian-specificity move is to connect the Deccan basalts, the coconut-shell industry, and the Green Hydrogen Mission into a single industrial narrative — India already exports the world’s adsorbent of choice for water and air; the next step is exporting the adsorbent and the storage geology for carbon.

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Direct Air Capture and Activated Carbon for UPSC: Full Notes on CO2 Removal, Pollutant Adsorption and Indian Industry

Gaurav Tripathi Sir

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Gaurav Tripathi Sir

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