Carbon Dioxide

• The air contains a mixture of different gases, which we inhale when we breathe. However, the gases humans exhale are different from those we inhale. The difference in the concentration of carbon dioxide can be easily demonstrated. Obtain some lime water, which is a solution of calcium hydroxide that turns milky in the presence of carbon dioxide. A chemical supply store should have some. Put a straw into a small beaker of the solution and use a pump or some other device to send air through the straw. Then, with a fresh beaker of the same volume of lime water, breathe through the straw gently and observe the difference. The air we breathe contains about .04 percent carbon dioxide, whereas air expelled from our lungs contains about 4 percent, which is 100 times more. This shows how much more concentrated carbon dioxide is in the air we exhale than the air we inhale.
  
  

Lung Capacity

• Obtain a spirometer from an online store or local health facility, or you can make your own (see Reference 4). A spirometer is a device that measures how much air you breathe. A simple incentive spirometer will work. Seal your lips around the mouthpiece. Inhale a slow, normal breath. Record the volume of air. This is called the tidal air, the amount of air that is normally exchanged during a breath. Then breathe in deeply, getting in as much air as you can. Do not breathe in so deeply or violently that you harm yourself. Record this measurement. This is a good indication of your lung capacity, although it is not possible to completely fill or empty your lungs without harming yourself. Repeat the experiment with several other people, always cleaning the mouthpiece after each user. Note differences between people of opposite genders, different ages or different sizes. Look for patterns, if possible.
  
  

Breaths Per Day

• Work with a partner and count each other's breaths for one minute. Breathe very normally; it may be tempting to breathe slowly or deliberately, but try to be as natural as possible. Record this number. Put an incentive spirometer to your mouth and take a normal breath. Ask your partner to do the same after cleaning the mouthpiece. If you find it difficult to purposely take a normal breath, do it several times and average the volume. This is the average volume of your breath. Multiply the number of breaths you take in one minute by 60 to get the number of breaths that you take in an hour, then by 24 to get the number of breaths you take in a day. You can use this number to learn how much air you breathe. Multiply the number of breaths you take in a day by the average volume of your breath to calculate how much air you breathe in an average day. Do the same with your partner and compare results.
  
  

Pollution

• The air we breathe does not contain only gases. It is filled with particles, too. Some of these particles are considered pollution, and they are a concern because they are unhealthy for the environment and for humans. Cut some small squares out of cardboard and draw a small black box in the center of each. Make the squares and boxes about the same size. Use a hole punch to put a hole in the top of each, and use some thread to make a loop through the hole. Smear a little petroleum jelly in the black box and hang the squares in different places outside. Do not let them get wet. Leave the squares in place for three to five days. Remove the squares and examine the petroleum jelly in the boxes you drew. Look at the particles with a magnifying glass and estimate how many there are. If you have calculated how many breaths you take in a day, you can make an estimate of how many particles you breathe in.