Modeling the Accumulation and Depletion of Smog in Los Angeles

Alejandra De Obeso
Lauren Floyd
Dr. Nihat M. Gürmen
Prof. H. Scott Fogler




The city of Los Angeles was founded on September 4, 1781, under the name “El Pueblo de Los Angeles” and was incorporated to the United States on April 4, 1850.

As of 2002 the population of Los Angeles County was 9,806,577.

28% of the population in Los Angeles is under age 18.

The county of Los Angeles covers approximately 4,061 square miles (10,518 square kilometers).

The median household income for the city of Los Angeles in 1999 was $42,189.

The mean travel time to work was 29.4 min as of 2000.

Over 81% of all Los Angeles workers drive to work every day.

Los Angeles has over 15,600 acres of parkland.

Los Angeles is home to Griffith Park, the largest municipal park in the United States.


Pollutants tend to accumulate in the lowest layer of the atmosphere, the troposphere, especially over the cities. This is due to the phenomenon of thermal inversion. When this occurs a layer of warm air above traps the pollutants.  In addition, the topography of a city can worsen this effect, being the case of L.A. since it is surrounded by mountains.   


NO2+ hv → NO + O

O + O2 O3

O3 + NONO2 + O2

NO2 + VOC → products such as PAN

O3 + VOCs → aldehydes and free radicals

Burning gasoline in motor vehicles is the main source of nitrogen oxides. Powered by sunlight, NOx and volatile organic compounds (VOCs) react in the atmosphere to produce photochemical smog. The process of smog formation is the following:

    • Traffic increases the emissions of nitrogen oxides and VOCs in the early morning.
    • Later in the morning the NOx and VOCs start reacting to form nitrogen dioxide.
    • Intense sunlight breaks nitrogen dioxide molecules, increasing ozone concentration. Some of the nitrogen dioxide can react with the volatile organic compounds (VOCs) to produce toxic chemicals. Ozone also reacts with VOCs to produce aldehydes and free radicals.
    • As the sun goes down the production of ozone stops, and it may be consumed in several other reactions.


Winds may blow smog away, which is the case in the problem you are about to explore.

Temperature inversions can increase the production of smog, due to the reduction of atmospheric mixing. Therefore, the pollutants concentrate in the troposphere.

Topography is another factor, since hills and mountains surrounding a community may reduce the flow of air, and as a consequence develop temperature inversions.