Ground-Level Ozone

• Ozone is composed of three oxygen atoms and is primarily formed on the ground via a chemical reaction between nitrous oxide and various organic compounds. These chemicals are produced by cars, chemical solvents and industrial emissions. The combination of sunlight and hot weather causes the ozone to evaporate and form harmful concentrations in the air.
  
  

Particulate Matter

• Particulate matter is also often referred to as particle pollution. It is made up of organic particles like soil, metal and dust. Smaller particles, generally less than 10 micrometers, are small enough to form atmospheric clouds that can possibly be inhaled and cause serious problems in the heart and lungs.
  
  

Carbon Monoxide

• Carbon Monoxide is an odorless gas that is often the product of large-scale industrial emissions. According to the EPA, most emissions come from the internal combustion engines found in vehicles. Carbon Monoxide reduces oxygen delivery to the lungs in people, and at high enough concentrations, can even cause death.
  
  

Nitrogen Dioxide

• Nitrogen Dioxide is the combination of one nitrogen and two oxide atoms. It is also known as nitrous oxide and comes in gaseous and acidic forms. It is primarily a product of cars, buses and other industrial emissions. They are linked to detrimental respiratory effects in people but are better known for combining with other organic chemicals into ozone.
  
  

Sulfur Dioxide

• Sulfur dioxide is a highly reactive gas that is produced primarily by combustion of fossil fuels at large power plants. According to the EPA, Sulfur Dioxide is linked to a number of adverse health effects on people, primarily in the respiratory system.
  
  

Lead

• Lead is a metal that is found primarily in particle form. It comes from automobile emissions, though since the introduction of unleaded fuels, the amount of lead in the air dropped nearly 94 percent between 1980 and 1999. Lead is currently only found in heavy concentrations near lead smelters and is usually only found in aviation gasoline, which is still commonly leaded.