• Vehicular exhaust is a major cause of smog in Los Angeles.Los Angeles Smog image by CanonXTiGuy from Fotolia.com
  
  Smog, a term that is a combination of the words "smoke" and "fog," is air pollution that accumulates in large, industrialized cities such as Los Angeles. The type of air pollution in Los Angeles is called photochemical smog because it is formed from the interactions of sunshine combined with nitrogen oxides and reactive hydrocarbons emitted in car exhaust and industrial processes. The chief component of smog is ground-level ozone.
  
  

Vehicle Exhaust

• Heavy vehicular traffic on freeways and city streets in Los Angeles is a major source of nitrogen oxides, caused by burning gasoline. Vehicles and other mobile sources contribute about 50 percent of the reactive organic gases and about 55 percent of the nitrogen oxides in airborne pollution, according to Georgia Tech University. Other mobile sources of nitrogen oxide, such as construction equipment, contribute about 21 percent of the nitrogen oxides.
  
  

Industrial Processes

• Factories and power plants release smoke and gases into the atmosphere, contributing to pollution and the formation of smog. Fuel combustion at stationary sources such as factories contributes 22 percent of the nitrogen oxides in airborne pollution and about 50 percent of the reactive organic gases, according to Georgia Tech University.
  
  

Sunshine

• Los Angeles is well known for the abundant sunshine enjoyed by residents nearly year-round. Sunlight breaks nitrogen dioxide into nitrogen and oxygen, and atomic oxygen produces ground-level ozone, a primary factor in photochemical smog.
  
  

Thermal Inversion

• Pollution accumulates over cities in the troposphere, the lowest layer of the atmosphere, because of thermal inversion. A layer of warm air above traps the smog, especially when a city, such as Los Angeles is surrounded by mountains.