Atmospheric mixing

Before you can measure greenhouse gases, you need to understand atmospheric mixing – the way air and gases in the atmosphere are stirred and mixed. The wind plays a part in atmospheric mixing. When it isn’t very windy, emissions will stay around the area where they were emitted. Strong winds will blow the emissions away from the source.

The atmospheric boundary layer (ABL) is the thin layer of air closest to the ground. It can range from 100 to 3,000 metres. Greenhouse gases are mostly emitted close to the Earth’s surface within the ABL. The ABL changes height throughout the day and year depending on the temperature.

When the Earth is warm, the ABL is at its deepest – for example, during summer and afternoons. This means the emissions are going into a larger volume and become more spread out. This makes the concentration of gases look smaller than during the days and hours when temperatures are colder and the ABL is shallow. If we release the same amount of gases within a shallow ABL – for example, 200 m – they will be very dense in that air volume.