Bulletin 81

  Bulletin 81

  Odors - Detection and Control

  The air we breathe is a gas consisting of free molecules generally in a ratio of about 78% nitrogen, 21% oxygen, 0.3 carbon dioxide, variable water content, and traces of helium, neon, ozone and other gases.

  In addition, there are contaminants which can be broadly classified as either particulate or gaseous.

  Particulate contaminants vary in size and composition from normal household dust to microscopic particles or even virii.  Filtration is the recommended method to remove particulate contaminants.

  Gaseous contaminants cover a wide range of composition.  All of them consist of free molecules among the air molecules.  Gaseous contaminants that are often of concern are carbon monoxide, sulfur dioxide, hydrogen sulfide and other odorous gases of all kinds.

  Odorous substances may be detected only if they are vapors or gases; that is, free molecules of the substance must be dispersed or evaporated in the air.  Odor itself is defined as that property of a substance which excites the sense of smell.

  To be odorous, a substance is in a gaseous or vapor state.

  The human sense of smell is extremely sensitive.  The actual mechanics of how odors are perceived and identified is still somewhat of a mystery.  We do know that the olfactory system begins its complicated process of odor discernment with air passing through sensing elements in the nasal passage.

  Humans can identify dozens or maybe hundreds of different odors; trained chemists can correctly choose from thousands.   Animals, on the other hand, have an even better sense of smell (depending on the animal and type of odor).  No one knows how keen this sense of odor is in insects, but we do know they have it.

  The principle function of the olfactory system amongst all animals is to serve as a warning system.  Thus, the olfactory warns the body against consuming spoiled food, contaminated water, etc.  The olfactory also reacts to pleasant odors.  Amongst some animals, certain scents are essential to mating.  Even amongst humans there is a certain mystique associated with the allure of exotic perfumes.  Humans generally classify odors into three categories . . . good, bad, or indifferent and usually agree with one another on what constitutes bad.

  The human olfactory therefore is able to discriminate good or pleasing odors from bad odors - and, of course, all of the infinite variety of odors between the very good and the very bad.  Even slightly offensive odors are readily noticeable to many human beings.

  When people declare war on a bad odor nowadays, they break out an arsenal of covering perfumes, masking scents and neutralizers and other kinds of sprays.  They install recirculating fans and blowers and they force air through chemical filters, charcoal filters, fine porosity filters, combinations of filters, etc., etc., etc.   It seems we humans really go after those bad odor molecules floating in our air.

  Nature, on the other hand, employs a much simpler and more direct method.  Did you ever walk outside after a thunderstorm and notice how clean and fresh the air smells?  Thunderstorms are nature's way of wiping out odors and, as usual, nature does a much better job than we do.  The secret, of course, is in the ozone produced by every bolt of lightning.  The larger and longer the bolt, the more ozone it makes.

  As soon as ozone (which is O³) is made from oxygen (O²) in the air, the ozone begins to react with odor causing molecules.  Sulfur oxides and nitrogen oxides are oxidizable to sulfates and nitrates; hydrocarbons break apart into smaller molecules and finally single carbon atoms on the way to becoming carbon dioxide (CO).  These are reactions that oxygen (O²) could eventually accomplish, but the ozone (O³) gets the job done much faster.

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