Monday, 20 April 2026
Contrail formation depends heavily on altitude. Higher pressure levels (lower hPa values) correspond to higher altitudes with colder temperatures. The table below shows typical conditions across the 8 pressure levels ChemTracker monitors.
Contrail formation follows the Schmidt-Appleman criterion, a thermodynamic model that predicts whether the mixing of hot engine exhaust with cold ambient air will produce a visible trail. The following thresholds determine when and how contrails appear.
Every analysis cycle, ChemTracker's prediction engine processes atmospheric and flight data to produce real-time contrail probability scores.
ChemTracker operates worldwide. The ADS-B flight tracking network covers airspace across North America, Europe, the Middle East, East Asia, Southeast Asia, and Oceania, with expanding coverage in South America and Africa. Atmospheric data is sourced from global weather models that provide full planetary coverage at all monitored pressure levels.
Each user's detection radius extends 250 kilometres from their position, capturing all ADS-B-equipped aircraft within range. The system processes data from 3 redundant flight data sources to ensure continuous tracking even when individual feeds experience interruptions. Combined with atmospheric analysis refreshed every 10 seconds, ChemTracker provides near-real-time contrail prediction for any location on Earth where aircraft operate at cruise altitude.
Contrails form when hot, humid exhaust from jet engines mixes with cold ambient air at high altitudes. The key requirements are air temperature below approximately -39°C to -45°C (the Schmidt-Appleman threshold) and sufficient relative humidity over ice. At cruise altitudes between FL260 and FL450 (roughly 7,900 to 13,700 metres), these conditions occur frequently. When relative humidity over ice exceeds 100%, contrails persist and spread — these are known as persistent contrails.
ChemTracker analyses real-time atmospheric data across 8 pressure levels from 150 to 400 hPa, covering the full range of commercial aviation altitudes. For each aircraft, the engine calculates the Schmidt-Appleman criterion using temperature, pressure, and relative humidity over ice at the aircraft's flight level. It then runs 25 to 50 Monte Carlo simulations to account for uncertainty in atmospheric measurements, producing a probability score for contrail formation and persistence.
ChemTracker's prediction engine combines data from multiple atmospheric sources with real-time ADS-B flight tracking. The Monte Carlo simulation approach accounts for measurement uncertainty and spatial variability, producing probability-based predictions rather than binary yes/no outputs. Accuracy depends on the quality of available atmospheric data and the aircraft's proximity to pressure level boundaries, but the multi-source redundancy approach ensures robust predictions even when individual data sources have gaps.
ChemTracker processes 1,248 atmospheric data points per analysis cycle, covering temperature, relative humidity over ice, wind speed, and wind direction across 8 pressure levels (150, 175, 200, 225, 250, 300, 350, and 400 hPa). It combines this with live ADS-B transponder data from 3 redundant flight data sources, tracking aircraft positions, altitudes, speeds, and headings within a 250-kilometre detection radius. All data is refreshed every 10 seconds.
ChemTracker combines live atmospheric data with real-time flight tracking to predict contrail formation. Point your phone at the sky and see every aircraft in your area. Start your free 14-day trial.
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