It's Getting Harder and Harder to Breathe...

An air pollutant can be defined as an "airborne gas or particle that occurs at a concentration capable of harming humans and/or the environment" (Spaulding & Namowitz, 2005). There are several causes of air pollution including natural causes such as volcanoes. However, it is human activity that creates the pollutants which scientists are most worried about. Modern conveniences such as factories and automobiles spew all kinds of pollutants into the atmosphere. These pollutants can lead to problems such as health problems, acid rain, smog, the depletion of the ozone layer, and global warming (Spaulding & Namowitz, 2005).

The Clean Air Act of 1970 identified the following common air pollutants. Read on to learn about their sources and effects on the environment.

• Carbon monoxide from automobile exhaust. This pollutant reduces the amount of oxygen in the air so it cannot get to body tissues. Carbon monoxide also affects a person's vision and reflexes.
• Nitrogen dioxide from the burning of fossil fuels in power plants and cars. Nitrogen dioxide can irritate lungs. This substance also causes acid rain and smog.
• Sulfur dioxide from the burning of fossil fuels, oil refineries, and volcanoes. Sulfur dioxide irritates the respiratory system and can cause acid rain.
• Particulate matter such as dust, smoke, ash, and soot from factories, paper mills, oil refineries, power plants, and volcanoes. Particulate matter causes respiratory problems and has been linked to certain cancers.
• Lead from smelters and battery plants. Lead can damage the nervous and digestive systems.
• Ozone from the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight. Ozone reduces lung function.

Smog
Remember how I posted earlier about the Industrial Revolution in England and all the air pollution it caused since it led to lots of greenhouse gas emissions? Well, the term "smog" was created to describe the mix of smoke and fog that gathered in the air above London in the early 1900s. This smoke and particulate matter (see above) came from factories (Smaulding & Namowitz, 2005).

Today, what we call "smog" is actually photochemical smog. This smog forms in air that is polluted by automobile exhaust. The nitrogen oxides and hydrocarbons in automobile emissions mix with radiation from the sun and cause the brown haze. This reaction also creates ozone and other harmful pollutants that can damage the environment and our health. The ozone in smog is also harmful to crops. So you aren't confused, the ozone that results from the pollutants that form smog is a powerful lung irritant while the ozone in the stratosphere is helpful to us since it provides a layer of protection from the sun's ultraviolet radiation (Smaulding & Namowitz, 2005).

Temperature inversion can also occur when smog is present. I'll post an interesting lab you can complete in the next blog entry. For now, here is some background information on temperature inversion.
Conditions in the atmosphere cause smog to be more or less severe. What usually happens is that the warm air that hovers near the Earth's surface mixes with the cooler air from higher above the Earth. This helps dilute the pollutants making the smog less severe. However, sometimes the air near the Earth's surface is cooler than the air above so convection does not occur and the air is not able to mix. This is what scientists refer to as temperature inversion. As you may have guessed, this causes more severe smog since the pollutants are not diluted. In this case, the warm air above is a sort of lid that traps the pollutants close to the ground which allows the smog to rise to dangerous levels (Spaulding & Namowitz, 2005).


The photo above shows temperature inversion (Wikipedia, 2005).

References

ClassroomClipart.com (n.d.). Smog clipart. Retrieved April 24, 2008 from http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Science/Environment&img=0

Spaulding, N.E. & Namowitz, S.N. (2005). Earth science. Evanston, IL: McDougal Littell.

Wikipedia (2005). Temperature inversion photo. Retrieved April 24, 2008 from http://en.wikipedia.org/wiki/Image:Sha1993_smog_wkpd.jpg