Carbon dioxide (CO2) levels in the atmosphere are measured through various methods:

1. Atmospheric Sampling: Air samples are collected from different locations worldwide using specialized instruments at monitoring stations or research facilities.

2. In Situ Measurement: Instruments like infrared gas analyzers or gas chromatographs directly measure CO2 concentrations at specific locations, such as towers, aircraft, or satellites.

3. Remote Sensing: Satellite-based instruments detect and analyze specific wavelengths of light reflected or emitted by the Earth’s atmosphere to estimate CO2 concentrations.

4. Flask Sampling: Air samples are collected in flasks and transported to laboratories for analysis.