Last updated 3-16-16
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Field Lab 5: Global Warming
Detecting water vapor in Car Exhaust

Car Exhaust contributes a great deal to pollution. It also contributes to global warming by the emission of carbon dioxide and water vapor. The warming isn't from the hot exhaust (which does contribute some) but from the fact that carbon dioxide and water soak up heat from the sun and from heat radiating from the ground.

In this experiment we want to detect water vapor coming from car exhaust. Since in the on-campus lab we proved that combustion produced carbon dioxide, we don't have to do that for this lab. 

The source of the water and the carbon dioxide is from the burning of the gasoline in the engine cylinders. Gasoline is a mixture of hydrocarbons with 6 to 10 carbons. Hydrocarbons are chains of carbons with hydrogen atoms attached (see molecule at top of image). In the picture carbon atoms are gray and hydrogen atoms are white.

Gasoline and oxygen enter the cylinder and a spark ignites the mixture. The spark begins the break up of the gasoline molecules and the oxygen molecules. Oxygen starts combining with the carbon atoms to form carbon dioxide (CO2) and oxygen also combines with the hydrogen atoms to form water (H2O). Both of these reactions give off energy. Some of the energy starts the break up of other gasoline molecules, which further allows more oxygen to combine with the freed up carbon and hydrogen atoms. In a flash a trillion trillion gasoline molecules are disintegrated and now just water and carbon dioxide remains.

All of the energy released as the gasoline molecules break up and combine with oxygen creates high pressure of carbon dioxide and water vapor in the engine cylinder. This pressure is used to push the cylinder down and make the car go.  After the piston gets pushed down and is heading back upward, the hot gases (CO2 and H2O vapors) are released to the exhaust system shown below...
In the above picture, the exhaust manifold is the first set of pipes that combine the exhausted gases from the cylinders into one pipe. The exhaust is then routed to the muffler to reduce the explosive sound that came from the gasoline exploding in the cylinders. A catalytic converter (not shown) comes before the muffler and converts unburned gasoline to carbon dioxide and water. The exhausts exits the tail pipes. It's at the tail pipe where we want to detect the water vapor.

The key to detecting water vapor from car exhaust is to start with a car with a cold engine.

No, it doesn't have to be this cold.

Evidence of water can be any of the 5 below methods.  You only need to take a picture of one of them.

Evidence #1 (cloud): If the air is cold, the normally invisible water vapor turns to droplets of water and a cloud forms behind your tail pipe. If this is the case, just take a picture of your car (or someone's) whose exhaust is showing the presence of water by condensing into visible water droplets (a cloud). This is only likely in December and January.
By the way, if this was burning oil, it would be blue-gray smoke. If it was excess unburnt gasoline, then it would be black smoke.

Evidence #2a (liquid water): Again, detecting water is best done when a car engine has just started up. (Note: The water is always there, but when the exhaust is very hot or the weather is hot, then it's harder to get the water to condense).  If the engine is too hot, then the water will not condense on the tail pipe and will not be seen. Warning: turn off engine before taking pictures. If you see water inside the tail pipe, take a picture.

Evidence #2b (liquid water): On my friend's Honda, I noticed water spitting from the tail pipe. I first noticed it by feeling the exhaust from about 1 foot away. Drops of water was hitting my hand and felt cool as they evaporated. I also could see drops of water on the driveway.  If you see drops of water on the ground coming from tail pipe, take a picture.
 Again, turn off engine before taking pictures. I don't want you getting run over by your own car.

Evidence #3 (Condensation on cool object): If you can't see liquid water on tail pipe or on the ground, you can try holding a cool object near the tail pipe. Make sure car is in park! Here I'm using the 250mL beaker to show that it fogs up when it came near the exhaust. You can use a regular glass drink glass.  A shiny cooking pan might work good too. Note: The condensation may only last for a few seconds. Just place the glass or metal in the exhaust for a few seconds and remove it after you see condensation. You might have time to take a picture before it evaporates. In hot weather, you may have to put some ice in the beaker.
This method is almost guaranteed to get visible condensation.
   
Evidence #4 (Feeling of moisture): Even when there's no condensation, you can feel moisture in the air. Car in Park! In this picture there are water drops on my hand from the tail pipe, so it was easy. But even without liquid water, you can sense the moisture. If the other methods fail, this might work for you. If so, take a picture of your hand.  It doesn't need to be this near the tail pipe.

Either send the photo you take to chm107@chemistryland.com, or you can send it via text message to my cellphone at 480-202-2993.  If sending via text message, be sure to include your name.