The Science and Impact of Non-CO₂ Aviation Emissions
Aviation warming is driven not only by long-lived CO₂, but also by short-lived, high-intensity effects: contrails/contrail cirrus, soot (nvPM), SOx-derived aerosols, and NOx chemistry. The lever is fuel chemistry.
1) The Aviation Emission Spectrum: CO₂ vs. Non-CO₂
Aviation’s climate footprint (at a glance)
CO₂ persists for centuries, while non-CO₂ effects are short-lived but dominate near-term warming.
Key climate impact drivers
Contrail cirrus, nvPM soot, SOx, and NOx chemistry.
| Feature | CO₂ Effects | Non-CO₂ Effects |
|---|---|---|
| Persistence | Centuries. | Hours to days. |
| Share of Total Impact | ~1/3. | ~2/3 (≈66%). |
| Primary Culprits | Total carbon. | Aromatics, naphthalene, sulfur. |
| Mitigation Focus | Lifecycle carbon + efficiency. | Fuel chemistry + strategic routing. |
2) The Physics of the Exhaust: From Aromatics to Ice
Chemistry → particles → clouds
Polycyclic aromatics (notably naphthalene) form soot that seeds ice crystals in cold, humid cruise conditions.
Practical takeaway
Contrail persistence is strongly influenced by soot particle density, linked back to aromatic fraction.
3) Quantifying the Impact: Dominance of Non-CO₂ Effects
Net Radiative Forcing (NRF)
NRF captures the net imbalance in radiation; contrail-induced cloudiness is a major driver.
Short-lived leverage
Reduce precursors and you reduce warming quickly (hours to days), unlike CO₂.
Impact split (illustrative)
Approximate share of warming: CO₂ (~1/3) vs non-CO₂ (~2/3).
Near-term “cooling opportunity”
4) Regulatory Phase Shift: Regulation (EU) 2024/2493
From voluntary to legal compliance
Non-CO₂ effects are moving into mandatory monitoring and reporting; fuel chemistry becomes compliance-critical.
NEATS
Weather-based modelling estimates CO₂e per flight. Missing chemistry data can trigger “worst-case” defaults.
Monitoring mandate timeline
Jan 1, 2025 — Monitoring mandate begins
StartAirlines track and monitor non-CO₂ effects per flight.
Mar 31, 2026 — First verified reporting deadline
VerifiedReported data on soot, aromatics, sulfur becomes visible to regulators.
Future — Integration into pricing mechanisms
ETSHigh-aromatic/high-sulfur fuels may face financial penalties.
Default values (worst-case inputs)
Compare your fuel vs default values
Leave blank to simulate “missing data”.
5) Technical Gap: Why SAF Isn’t a Near-Term Cure-All
The SAF reality check
Economics, supply constraints, and blend limits restrict how quickly SAF can remove soot precursors at scale.
The blend wall
Many SAF streams lack aromatics; legacy sealing requirements impose blending limits, retaining fossil fractions.
| Constraint | Data Point | Consequence |
|---|---|---|
| Economic | e-SAF ~13×; Bio-SAF ~3–5× vs fossil jet | Barrier to wide adoption. |
| Supply | ~1.6% of global demand | Shortfall vs mandates. |
| Technical | 50% blend limit (ASTM D7566) | Fossil fraction remains → precursors persist. |
6) Empirical Evidence: TERC Test Results
Headline results
Aromatics ~8.5% (vs ~18–25%). Full load particle number down ~40–50%, mass down ~30–40%. Sulfur down ~99.7% to <10 ppm.
Why it matters
Fewer particles → fewer ice nuclei → potential for thinner/shorter-lived contrails under suitable conditions.
Illustrative reductions (midpoints)
Midpoints: Full load (number 45%, mass 35%); Idle (number 35%).
Quick reference
7) Summary of Insights
From commodity to technology
Fuel chemistry (soot/sulfur/aromatics) becomes measurable climate and compliance performance.
Compliance enabler
Low-aromatic, low-sulfur fuels can help avoid punitive defaults under MRV regimes.