ACA Level 3+ — Neutrality: How Airports Procure Carbon Credits to Offset Scope 1, 2 & Staff Business Travel Emissions
What Level 3+ requires — offsetting all Scope 1, Scope 2, and staff business travel emissions — which credit programmes qualify, how to select projects, and how Canopy streamlines the procurement process.
By Koorosh Behrang & Abhishek Das • • 10 min read
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S1+S2+Travel
Emissions Covered
Scope 1, Scope 2, and staff business travel must be offset
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5 Programmes
ACA-Approved
Verra, Gold Standard, ACR, CAR, UK WCC
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Annual
Verification Cycle
ISO 14064 third-party verification required
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What Level 3+ (Neutrality) Requires |
Airport Carbon Accreditation (ACA) Level 3+ (Neutrality) represents the point where airports transition from measuring and reducing emissions to actively offsetting their remaining impact. This is not a starting level. Airports must first complete Levels 1 (Mapping), 2 (Reduction), and 3 (Optimisation), demonstrating active carbon management before entering Level 3+.
Level 3+ requires airports to offset all remaining Scope 1 and Scope 2 emissions, as well as Scope 3 staff business travel emissions, after all reduction measures have been applied. Every tonne of direct emissions from ground vehicles, heating systems, and on-site equipment (Scope 1), purchased electricity and district heating (Scope 2), and airport operator staff business travel (Scope 3 Category 6 under the GHG Protocol) must be counterbalanced with retired carbon credits from ACA-approved programmes.
Level 3+ Accreditation Pathway
Prerequisite: Completion of Levels 1, 2, and 3 with verified progress. Airports cannot jump to Level 3+ without demonstrating years of consistent emissions reduction.
Offset requirement: All Scope 1, Scope 2, and staff business travel (Scope 3 Category 6) emissions must be offset using credits from ACA-approved programmes. No partial or estimated offsets are acceptable.
Retirement requirement: All purchased credits must be retired on the relevant carbon registry, with the airport named as the beneficiary. Credits cannot be traded, banked, or used by other entities.
Annual third-party verification by an ISO 14064-3 accredited body is mandatory. The airport's accreditation is renewed annually upon successful verification.
This is where carbon credits enter the ACA framework for the first time. In earlier levels, airports focus on operations and efficiency. Level 3+ introduces the voluntary carbon market (VCM) as an integral part of the accreditation process, requiring airports to become sophisticated credit procurers and portfolio managers. It also marks the first level where a Scope 3 emission source — staff business travel — enters the offset boundary, signalling ACA's expanding view of airport responsibility beyond the fence line.
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ACA-Approved Credit Programmes |
ACA maintains a restricted list of approved voluntary carbon credit programmes to ensure quality control and additionality. The five major approved programmes are listed below. Airports must source credits exclusively from ACA-approved programmes, even if other registries are widely accepted in the global VCM. This constraint shapes procurement strategy and project selection.
Verra (VCS)
Largest voluntary registry, broadest project diversity
The Verified Carbon Standard (VCS) is the world's largest voluntary registry by volume. Verra credits span renewable energy, methane capture, forestry, REDD+, and energy efficiency across all geographies. Verra units are CORSIA-eligible, making them valuable for airlines that also fall under ICAO regulations. Price range typically $5-15/tCO2e for standard projects, higher for premium projects with strong co-benefits.
Gold Standard
Strong SDG alignment, preferred by European airports
Gold Standard credits are designed to deliver sustainable development co-benefits alongside climate mitigation. European airports often prefer Gold Standard due to its rigour and SDG credentials. Projects include cookstoves, water filtration, renewable energy, and agroforestry, predominantly in Africa and South Asia. Credits include both Certified Emission Reductions (CERs) transitioned from the Clean Development Mechanism and new Gold Standard issued credits. Price range typically $10-25/tCO2e.
American Carbon Registry (ACR)
US-focused, strong forestry and methane projects
ACR is the oldest voluntary carbon registry in the United States. Projects are predominantly North American, with significant exposure to forestry management, landfill methane capture, and livestock management. ACR credits are often used by US and Canadian airports. Prices typically range from $8-20/tCO2e, with methane projects commanding premiums due to their additionality.
Climate Action Reserve (CAR)
North American focus, rigorous protocols
CAR is known for exceptionally rigorous project protocols and baseline setting. Projects include landfill methane, manure management, livestock efficiency, and coal mine methane. CAR projects have strong additionality credentials and low leakage risk, making them attractive to airports seeking the highest quality offsets. Price range typically $15-30/tCO2e due to premium quality.
UK Woodland Carbon Code (WCC)
UK-specific forestry, strong additionality verification
UK WCC credits are issued for UK woodland creation and management. This programme has become increasingly attractive to UK and European airports seeking domestic offsets with strong additionality assurance. Credits are generated by planting trees on land that would not otherwise be afforested. Price range typically $12-22/tCO2e.
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Critical: Retirement Requirement All credits must be permanently retired on the relevant registry with the airport as the beneficiary. Credits cannot be traded forward, banked for future years, or used by intermediaries. The retirement certificate becomes part of the airport's annual ACA verification documentation. |
Portfolio strategy typically involves spreading purchases across multiple programmes. An airport might use Verra for renewable energy projects (large scale, lower cost), Gold Standard for co-benefit alignment (SDG reporting), and ACR/CAR for methane projects (high additionality). Domestic airports often use UK WCC to support local environmental goals.
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Scope 1, Scope 2 & Staff Business Travel: What Needs Offsetting |
The offset requirement applies to every tonne of Scope 1 (direct), Scope 2 (energy-related), and staff business travel (Scope 3 Category 6) emissions that remains after all reduction measures. Calculating this number accurately is the foundation of Level 3+ procurement strategy.
Scope 1 Emissions (Direct)
On-site fuel combustion and equipment operation
Scope 1 includes: ground fleet vehicles (ground handling, maintenance, shuttle buses), backup generators, heating and cooling systems using natural gas or oil, de-icing equipment, fire training facilities, and any on-site fuel combustion. For a mid-size European airport, Scope 1 typically accounts for 30-40% of total direct and energy emissions.
Scope 2 Emissions (Energy-Related)
Purchased electricity, district heating, and cooling
Scope 2 includes: purchased electricity for terminal operations, air traffic control, lighting, HVAC systems, and all electrical equipment. This is typically the largest component of airport emissions. Airports can reduce their Scope 2 offset requirement through renewable energy contracts (PPAs, green tariffs). Market-based accounting allows airports to claim zero Scope 2 emissions if they have 100% renewable energy contracts. Location-based accounting reflects the actual grid mix and typically requires larger offsets.
Example: A mid-size European airport might have 15,000-25,000 tCO2e of Scope 1+2 emissions annually. With a 50% reduction pathway in place (solar installations, fleet electrification, district heating conversion), the airport would need to offset 7,500-12,500 tCO2e at $10-15/tonne = annual spend of $75,000-$187,500.
Staff Business Travel (Scope 3 Category 6)
Airport operator employee travel — the first Scope 3 source in ACA
Level 3+ is where ACA first extends the offset boundary beyond the airport fence line. Staff business travel — classified as Scope 3 Category 6 under the GHG Protocol — covers flights, rail journeys, and other business trips taken by the airport operator's employees. This typically adds 500-2,000 tCO2e per year for a mid-size airport, depending on workforce size and travel policies.
Important distinction: This covers only airport operator staff travel (Category 6 — Business Travel), not employee commuting (Category 7) or third-party travel. The data source is typically the airport operator's corporate travel management system or expense reports.
The calculation is straightforward: Total Scope 1 + Scope 2 + Staff Business Travel Emissions minus Verified Reductions = Offset Requirement. As airports complete more reduction projects, the offset requirement shrinks — meaning procurement needs change year to year. A mature Level 3+ airport might see offset requirements plateau once all viable reduction measures are exhausted.
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Selecting the Right Credits |
Credit selection is the core procurement decision. All ACA-approved credits are technically acceptable, but not all are strategically aligned. Airports must balance cost, project type, vintage, geography, and impact narrative.
Project Type Trade-offs
Nature-based (forestry, REDD+): Lower cost ($5-10/tCO2e), high volume available, but carry permanence and reversal risk. Not suitable for airports seeking to support local environmental goals unless paired with active management.
Renewable energy: Low cost ($5-12/tCO2e), strong supply, but additionality increasingly questioned in mature markets. Still acceptable for ACA purposes if sourced from emerging markets.
Methane capture: Strong additionality, verified reductions, $12-20/tCO2e. Popular with airports due to rigour. Includes landfill methane, agricultural methane, coal mine methane.
Cookstoves & clean energy access: $15-25/tCO2e, strong SDG co-benefits, popular with airports wanting impact narrative. Gold Standard preferred for these projects.
Vintage & Geography Considerations
Vintage: ACA typically requires credits issued within the last 5 years. Older vintages are discounted and harder to place. A mid-procurement strategy uses recent vintage (last 2 years) for verification purposes and slightly older vintages (3-5 years) for cost optimization.
Geography: No geographic restriction exists. However, many airports prefer local or regional projects (European airports sourcing from EU/UK projects, Asian airports from South-East Asia) for narrative and supply chain alignment. Local projects often command a premium but support sustainability narrative.
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Portfolio Rule: Diversification Best practice is to distribute the offset requirement across multiple project types and programmes. A typical airport portfolio might be: 40% renewable energy (cost), 30% methane capture (additionality), 20% cookstoves (impact), 10% local forestry (narrative). This reduces price volatility and market concentration risk. |
Procurement typically occurs 4-6 weeks before the annual verification deadline to ensure credits are retired and documented in time. Bulk purchasing (5,000+ tonnes) often attracts 10-15% discounts, making multi-year pooling strategies cost-effective.
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Verification and Reporting |
Level 3+ accreditation is renewed annually through third-party verification. The verification process is rigorous and includes a comprehensive audit of the airport's emissions inventory, reduction measures, and credit portfolio.
Annual Verification Checklist
Emissions inventory: Complete Scope 1, Scope 2, and staff business travel calculation with supporting documentation (utility bills, fuel invoices, vehicle logs, corporate travel records).
Reduction measures: Evidence of all reduction projects completed, operational improvements, and energy efficiency gains.
Credit portfolio: List of all purchased and retired credits with retirement certificates from the relevant registries.
ACA administrator (WSP) conducts desk review and site visit. Typical timeline: Fiscal year emissions reported, 3-6 months for verification, accreditation renewed if all requirements met.
Common pitfalls: Late retirement of credits (must be completed before verification deadline), vintage issues (old credits rejected), double-counting (same credit claimed by multiple parties), insufficient documentation (invoices, contracts, retirement certificates missing). Airports that fail verification lose accreditation until corrections are made.
The verification process is an opportunity to refine procurement strategy. Verifiers often flag market inefficiencies: prices paid relative to market rates, project types underutilised, opportunities for volume discount. Airports that use these insights build stronger programmes year on year.
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How Canopy Supports Level 3+ Airports |
Carbon credit procurement can be managed manually, but as airports scale their offset requirements, the operational burden becomes significant. Climate Decode's Canopy platform automates the calculation, curation, procurement, and reporting workflow.
Canopy Workflow for Level 3+ Airports
Step 1: Emissions Calculation — Input annual Scope 1, Scope 2, and staff business travel inventory data from TerraNova or manual sources. Canopy automatically calculates residual emissions after verified reductions.
Step 2: Credit Curation — Canopy curates available credits from all five ACA-approved programmes, filtered by project type, vintage, geography, price, and co-benefit criteria.
Step 3: Portfolio Assembly — Canopy recommends a diversified portfolio aligned with the airport's budget, timeline, and impact goals. The platform can build portfolios optimising for cost, additionality, geography, or co-benefits.
Step 4: Procurement & Retirement — Canopy manages the vendor procurement process and coordinates credit retirement on the correct registry, ensuring the airport is named as the beneficiary.
Step 5: Verification Support — Canopy generates audit-ready reports including retirement certificates, vintage verification, budget tracking, and ACA compliance checklists.
From Inventory to Accreditation
Canopy automates the offset procurement workflow for Level 3+ airports, reducing manual data management from months to weeks. The platform integrates with emission inventory tools, carbon registries, procurement platforms, and ACA verification processes — transforming a fragmented, manual operation into a cohesive, defensible system.
For airports managing 10,000+ tCO2e annually, Canopy typically reduces procurement costs by 10-15% through better price visibility and volume aggregation, while simultaneously improving compliance and audit readiness.
References
ACI Europe, Airport Carbon Accreditation Programme. ACA, Level 3+ (Neutrality) Accreditation Requirements & Guidance. ISO 14064-1:2018, Greenhouse gases — Quantification and reporting of greenhouse gas emissions at the organization level. ISO 14064-3:2019, Greenhouse gases — Quantification and reporting: verification and validation. Verra, VCS Programme Guide. Gold Standard, Gold Standard for the Global Goals. Climate Decode, Canopy: Carbon Credit Procurement & Portfolio Management.
Ready to Achieve ACA Level 3+ Accreditation?
Climate Decode's Canopy helps airports calculate Scope 1, Scope 2, and staff travel residual emissions, curate ACA-approved carbon credits, and build audit-ready portfolios aligned with Level 3+ requirements and annual ISO 14064 verification cycles.
About the Authors
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Koorosh BehrangFounder, Climate Decode Koorosh leads Climate Decode's mission to decode carbon markets and drive real decarbonisation. He brings deep expertise in carbon market infrastructure, compliance frameworks, and enterprise carbon management systems. |
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Abhishek DasVoluntary Carbon Markets & Residual Emission Procurement Strategy, Climate Decode Abhishek works on Climate Decode's voluntary carbon markets and residual emission procurement strategy, bridging corporate net-zero target setting with emerging carbon credit frameworks and procurement workflows. |