Denver's Brown Cloud Clean air has long been an important reason moved to Colorado. email to friend
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Clean air has long been an important reason people moved to Colorado. By the 1970s, the pollution hanging over the city had a name - the brown cloud. Denver's location at the foot of the Rocky Mountains make it prone to temperature inversions in which warm air traps cooler air near the ground, preventing pollutants from rising into the atmosphere. Learn more about temperature inversions with this eye-catching hands-on science experiment.

Materials

Four empty identical bottles (mouth of the bottle should be at least 1 1/2 inches in diameter)
Access to warm and cold water
Food coloring (yellow and blue)
3 x 5 inch index card or an old playing card

Experiment
Video

1. Fill two bottles with warm water from the tap and the other two bottles with cold water. Use food coloring to color the warm water yellow and the cold water blue. Each bottle must be filled to the brim with water.

2. Hot over cold: Place the index card or old playing card over the mouth of one of the warm water bottles. Hold the card in place as you turn the bottle upside down and rest it on top of one of the cold water bottles. The bottles should be positioned so that they are mouth to mouth, and the card is separating the two liquids.

3. Carefully slip the card out from in between the two bottles. Make sure that you are holding onto the top bottle when you remove the card. Observe what happens to the colored liquids in the two bottles.

4. Cold over hot: Repeat steps 2 and 3, but this time place the bottle of cold water on top of the warm water. Observe what happens.

The second picture shows the same demonstration using an aquarium in place of the bottles to produce a layering effect.

How does it work?

Hot air balloons rise because warm air is lighter than cold air. Similarly, warm water is lighter in weight or less dense than cold water. When the bottle of warm water is placed on top of the cold water, the more dense cold water stays in the bottom bottle and the less dense warm water is confined to the top bottle. However, when the cold water bottle rests on top of the warm water, the less dense warm water rises to the top bottle and the cold water sinks. The movement of warm and cold water inside the bottles is referred to as the convection current. In our daily life, warm currents can occur in oceans, like the warm Gulf Stream moving up north along the American Eastern Seaboard. Convection currents in the atmosphere are responsible for the formation of thunderstorms as the warm and cold air masses collide. Although all of the attention is focused on bottles where the colored liquids are mixing, the other set of warm and cold water bottles help to illustrate another important phenomena that occurs in the atmosphere during the winter months. During daylight hours, the sun heats the surface of the earth and the layer of air closest to the earth. This warm air rises and mixes with other atmospheric gases. When the sun goes down, the less dense warm air high up in the atmosphere often blankets the colder air that rests closer to the surface of the earth. Because the colder air is more dense than the warm air, the colder air is trapped close to the earth and the atmospheric gases do not mix. This is commonly referred to as temperature inversion.

Additional Info

What are the results of temperature inversion? Air pollution is more noticeable during a temperature inversion since pollutants such as car exhaust are trapped in the layer of cold air close to the earth. As a result, state agencies in many parts of the country oxygenate automobile fuels during winter months with additives like MTBE in an attempt to reduce the harmful effects of trapped pollution. More Weather Experiments