How ChemTracker Works

ChemTracker is a real-time flight tracking application that predicts whether aircraft overhead are producing visible contrails. Using live ADS-B flight data, atmospheric conditions from 8 pressure levels, and the Schmidt-Appleman thermodynamic criterion, ChemTracker analyzes every aircraft within 250km of your location and determines if conditions support contrail formation. Available worldwide as a web app with a 14-day free trial.

ChemTracker was built for people who look up. Whether you are an aviation enthusiast, a sky watcher, or someone who wants independent tools to understand what is happening in the atmosphere above your home, ChemTracker gives you the data to investigate for yourself. No speculation — just real-time flight positions, atmospheric measurements, and peer-reviewed science applied to every aircraft overhead.

What ChemTracker Does

ChemTracker is a flight tracking and contrail prediction tool that combines live aviation data with atmospheric science to show you which aircraft are leaving trails and why. Here is what the app does:

• Tracks all aircraft within 250km of your position in real-time — using ADS-B transponder data, ChemTracker shows every commercial flight, private aircraft, and cargo plane operating in your area on a live map that updates continuously.
• Predicts contrail formation using atmospheric science — by combining temperature, humidity, and pressure data from multiple altitude levels with the Schmidt-Appleman thermodynamic criterion, ChemTracker calculates whether each aircraft is likely to produce a visible trail.
• Shows which specific aircraft are leaving trails and why — every aircraft on the map receives a contrail score. Tap any plane to see its flight details, altitude, atmospheric conditions at that altitude, and the scientific basis for its trail prediction.
• Sends alerts when spraying conditions are detected — Golden Hour alerts notify you when atmospheric conditions in your area are most favourable for persistent, visible contrail formation, so you can step outside and observe.
• Lets you report and photograph trails to help improve detection — the Field Reports feature allows you to photograph trails, tag the responsible aircraft, and log your observations. Your reports contribute to a growing dataset that helps refine prediction accuracy.

The Science Behind the Prediction

ChemTracker's contrail predictions are based on established atmospheric science. The system combines five layers of data to determine whether a given aircraft, at a specific altitude, in current atmospheric conditions, will produce a visible trail. Here is how each layer works:

1. Flight Data from the ADS-B Network

ADS-B (Automatic Dependent Surveillance-Broadcast) is a surveillance system in which aircraft broadcast their position, altitude, speed, heading, and identification via radio signals. ChemTracker receives this data in real time from a global network of ground-based receivers. For each aircraft, the app knows its exact position, cruising altitude, aircraft type, registration, airline, and route — all updated every few seconds.

2. Weather Data from 8 Atmospheric Pressure Levels

Contrails form at specific altitudes where conditions are right — aircraft at cruise altitude (10,000–12,000m) travel through air as cold as −55°C, and relative humidity above 100% with respect to ice is required for persistent contrails. ChemTracker retrieves atmospheric data from 8 pressure levels between 150 and 400 hPa, corresponding to altitudes of roughly 7,000 to 14,000 metres (23,000 to 46,000 feet), totalling 1,248 atmospheric data points per scoring cycle. At each level, the app reads temperature, relative humidity over ice, and wind speed. This data comes from global numerical weather prediction models and is updated multiple times per day.

3. The Schmidt-Appleman Criterion

The Schmidt-Appleman criterion, first described in 1953 and still the standard model for contrail prediction, is the thermodynamic equation used by atmospheric scientists to predict contrail formation. It calculates the critical temperature below which contrails will form, based on ambient humidity, atmospheric pressure, and the overall propulsion efficiency of the aircraft engine. If the actual temperature at the aircraft's altitude is below this critical threshold, a contrail will form. If humidity is high enough, the contrail persists and spreads. If humidity is low, the trail dissipates quickly.

4. Monte Carlo Simulation

Atmospheric measurements have inherent uncertainty. Temperature and humidity readings are interpolated from weather model grid points that may be tens of kilometres apart. To account for this, ChemTracker runs 25 to 50 Monte Carlo simulations per aircraft, varying the input parameters within their known uncertainty ranges. The result is a probability-weighted contrail score rather than a simple yes/no prediction, giving you a more accurate picture of trail likelihood.

5. Solar Visibility Calculation

A contrail can form but still not be visible from the ground if the sun angle is wrong or if it is dark. ChemTracker factors in the time of day, sun position, and solar elevation angle to determine whether a predicted contrail would actually be visible to an observer on the ground. This is why the app's "Golden Hour" alerts are timed to periods when trail visibility is at its peak.

“According to ChemTracker's atmospheric analysis engine, running 25 to 50 Monte Carlo simulations per aircraft against live data from 8 pressure levels produces contrail predictions that far surpass simple yes/no models — giving observers the probability-weighted confidence they need to evaluate what they see in the sky.”

Key Features

ChemTracker includes a set of tools designed for observing, identifying, and documenting aerial activity. Each feature is built around the principle that you should be able to see what is in the sky, know what it is, and record what you observe.

• Live flight map with real-time positions — a continuously updating map showing every aircraft in your area. Aircraft icons indicate heading and type. The map centres on your location and extends to a 250km radius.
• Contrail scoring: CLEAR / DISPERSING / SPRAYING — every aircraft on the map is assigned a contrail score based on the atmospheric analysis. CLEAR means no trail is expected. DISPERSING means a short-lived trail that fades quickly. SPRAYING means a persistent, spreading trail that will remain visible for an extended period.
• Sky Scanner: point your phone at a trail to identify the aircraft — the Sky Scanner uses your phone's compass and orientation sensors to let you point at a trail in the sky and immediately see which aircraft made it, its flight number, altitude, and contrail score.
• Evidence packs: shareable flight cards with atmospheric data — generate a detailed flight card for any aircraft that includes its identification, route, altitude, atmospheric conditions at that altitude, contrail score, and the scientific basis for the prediction. Evidence packs can be downloaded and shared.
• Golden Hour alerts: notifications when trail visibility peaks — receive push notifications when conditions in your area are optimal for visible contrail formation. These alerts combine atmospheric predictions with solar visibility to tell you the best times to observe.
• Field reports: photograph and log unidentified trails — see a trail you want to document? Take a photo directly in the app, tag it with the time, location, and any nearby aircraft, and save it to your personal observation log. Field reports can be shared and help build a crowd-sourced record of trail activity.

Pricing

ChemTracker is designed to be accessible. The free tier gives you a live flight map and basic access, while the Pro plan unlocks the full analytical toolkit. Every new account starts with a 14-day free trial of Pro — no credit card required.

Who Uses ChemTracker

ChemTracker is used by a diverse community of people who share a common interest: understanding what is happening in the sky above them. The app serves three primary audiences:

• Sky watchers and aviation enthusiasts — people who enjoy tracking aircraft, understanding flight patterns, and learning about atmospheric science. ChemTracker provides a level of detail that goes beyond standard flight tracking apps by adding atmospheric context and contrail prediction.
• People concerned about aerial activity in their area — citizens who have observed persistent trails, unusual flight patterns, or unexplained aerial activity and want tools to identify and document what they see. ChemTracker replaces speculation with data.
• Citizens who want independent observation tools — people who believe in the value of public access to flight and atmospheric data, and who want to make their own observations and draw their own conclusions based on verifiable information.

Available Worldwide

ChemTracker works globally. The ADS-B network provides flight data coverage across North America, Europe, Asia, the Middle East, Africa, Oceania, and South America. Atmospheric data is sourced from global weather models that cover the entire planet. Wherever you are, if aircraft are flying overhead, ChemTracker can track them and predict contrail formation. The app works in any modern web browser on any device — no app store download required.

Frequently Asked Questions