We listed the 5 most abundant gases in the atmosphere in class on Monday.  Here is a list of several more important gases. 

Water vapor, carbon dioxide, methane, nitrous oxide (N₂O = laughing gas), chlorofluorocarbons, and ozone are greenhouse gases.  We'll discuss the greenhouse effect a little bit more later in class today and will learn more about it actually works when we get to Chapter 2. 

Carbon monoxide, nitric oxide, nitrogen dioxide, ozone, and sulfur dioxide are some of the major air pollutants.  We'll cover 2 or 3 of these in class on Friday and early next week.  You may have heard or read about an incident earlier this week where carbon monoxide from a malfunctioning hot water heater sickened 23 Virginia Tech students in an apartment complex.  Carbon monoxide concentrations indoors can easily and rapidly reach fatal levels.  Carbon monoxide levels in the atmosphere are much lower but can still represent a health hazard. 

Ozone in the stratosphere (a layer of the atmosphere between 10 and 50 km) is beneficial because it absorbs dangerous high energy ultraviolet (UV) light coming from the sun.  Without the protection of the ozone layer life as we know it would not exist on the surface of the earth.  Chlorofluorocarbons are of concern in the atmosphere because they destroy stratospheric ozone.   In the troposphere (the bottom 10 kilometers of the atmosphere) ozone is a pollutant and is one of the main ingredients in photochemical smog.