Research

Fumigation simulation

What the animation shows

This laboratory simulation shows 'fumigation' of air pollution that starts off above the inversion (e.g. 500 m above the ground). The ribbon of pollution begins moving up and down in a wavy pattern as the (invisible) turbulence in the bottom third of the frame disturbs the air above. As the convective boundary layer grows deeper, it draws the pollution down at several points and causes increased pollution levels near the ground. Slowly all of the polluted air is drawn down and mixed into the region below the inversion.

This event is common in coastal industrial regions and also at inland sites during mid-morning.

Laboratory convection experiments

The Geophysical Fluid Dynamics laboratory features a number of sophisticated water tanks in which simulations are performed of atmospheric flow and dispersion. A special 4,000-litre tank is used for studying the convective boundary layer.

Convection in the atmosphere occurs on sunny days with light winds. It is the process in which air in contact with the ground warms and rises as ‘thermals’. The rising air draws in cooler air from nearby. The warm air cools as it gets higher, loses speed and moves sideways as it reaches the inversion. Cooler air from above descends and the combined effect produces a circular motion often referred to as a convection cell. These cells can be up to 1-2 km in diameter. The motion is also very turbulent, which stirs up pollutants very quickly.

In the laboratory water tank, convection is achieved by allowing a saline solution to diffuse through a membrane at the top of the tank. The result is an upside-down model of the atmosphere. But we turn the cameras upside down so that the pictures are the same way up as the atmosphere!

Modified: 9/10/08