Monday, September 15, 2008

What is in the Air We Breathe?

Laura from Hollidaysburg, PA, was recently helping her parents clean her home, and she noticed how much dust there was on the tables, in the air, and coming from the couches! She wrote in asking: Where does dust come from and what happens to it when we breathe it in? About 21% of the air we breathe is actually oxygen, while the remaining air consists of other gases (e.g., nitrogen, argon, carbon dioxide). However, the air also consists of dust, tiny animals, and other stuff! Dust is defined as dry, solid particles that are less than 0.0625 millimeter in diameter, which is smaller than all grains of sand! Most dust is composed of mineral matter that originated from bare soil, plowed fields, river flood plains, and floors of desert basins. Dust also comes from ocean spray, smoke and ash produced by fires, decaying organic materials, and volcanic eruptions. The wind actually lifts up the dust particles and easily carries them long distances around the earth! The dust in your home can also be made up of dust, pollen, mold, sand, skin flakes, and pet dandruff. These air particles are actually the most common causes of allergies or asthma. Humans and animals can also act as carriers of dust and air particles because the air particles can cling to their skin or clothes. When you breathe in, you are also breathing in dust or air particles. Some of these air particles will get caught in your nose hairs, some will get caught in mucus in your airways, and some will make it into your lungs. However, don't worry too much about this, because most of what you breathe in will cling to the hairs on the inside of your nose. These hairs act as a filter, which works to trap the inhaled air particles inside your nose to keep them from traveling into your respiratory system. The hairs usually trap particles that are less than 5 nanometers in size (that is approximately 0.000005 mm!). Aside from the many nuisances of dust around your home, dust actually contributes to some beautiful sunsets and sunrises. That's right, dust is what makes sunsets and sunrises so pretty! The intense red and orange colors of the sky at sunset and sunrise are mainly caused by the scattering, or reflection, of sunlight off air and dust particles. So the next time you are cleaning your house or enjoying a beautiful sunset or sunrise, think of the dust that is contributing to these everyday events.

Little Lion Experiment:

This experiment will allow you to observe the types of air particles you breathe regularly.

Items Needed

  • 6 index cards
  • Scissors
  • A pen
  • 6 pieces of string
  • tape (scotch, masking, duct, or packing tape is good)
  • A magnifying glass
  • A ruler


  1. Cut squares into the center of each index card. Try to make all the squares the same size (e.g., about 2'' by 3'').
  2. Choose 6 locations within your home that you want to hang the air particle collectors. Some places to hang your air particle collector include: above your bed, on the inside or outside of a window, near a heating vent or air conditioner, above the cooking stove, on a wall near the floor or ceiling, on your main entry door, and under a tree.
  3. Write down the locations on the index cards so that each index card has a different location on it
  4. Write the starting date on each index card
  5. Cover the window on the index card with the tape so that the stick side up or out.
  6. Attach string to each index card, and then hang the cards at the appropriate locations.
  7. Wait a few days and then take the index cards down without touching the tape. Make sure to note the date. Which location had the most air particles collected? Were these locations inside or outside? Why do you think this is so? Think about where air is moving, and where the air particles could be coming from. Use your magnifying glass to examine the air particles up close. Can you recognize any common air particles?