Apr 15 2011
On Monday, we learned primarily about smog, or “smoky fog”, which is the dark, sooty pollution one can typically see over heavily populated industrial areas such as Pittsburgh or Mexico City. There are two main types of smog: “grey” smog and “brown” smog, which are obviously named as such due to their color.
Grey smog, or “industrial smog” is caused primarily by sulfur oxides (SOx) released by the burning of coal and other similar fossil fuels into the air which react with oxygen (O2) in the air forming sulfur trioxide (SO3).
- SOx + O2 –> SO3
The sulfur trioxide then reacts with the water vapor in the atmosphere to form the secondary air pollutant sulfuric acid (H2SO3) which is a major component of acid rain. The rain then condenses and falls, weathering both geological and manmade features.
- SO3 + H2O –> H2SO3
Brown smog is caused by the nitric oxide released by vehicles and other petroleum burners into the atmosphere. When a car’s combustion engine runs, it takes in about 78% atmospheric nitrogen (N2) and 21% atmospheric oxygen (O2), it then reacts the oxygen with the burning gasoline, uses the energy released to turn its wheels, and expels the resulting gases. Some of the gases that are expelled include nitrogen, carbon dioxide, and water vapor and droplets. The U.S. government does not regulate any of those emissions, but legislation is being constructed to regulate the emission of carbon dioxide. Currently, the government does regulate the emission of carbon monoxide (which is toxic), hydrocarbons (unburned fuel), and nitric oxide. Nitric oxide is regulated due to its creation of brown smog. The nitric oxide reacts with the atmospheric oxygen to form nitric dioxide (NO2), a red brown toxic gas that causes eye and respiratory irritation.
- NO + O2 –> NO2
The nitrogen dioxide can then react with sunlight to breakdown, releasing Oxygen atoms (O) which then react with atmospheric oxygen forming ozone (O3).
- NO2 + Sunlight –> NO + O
- O + O2 –> O3
The nitrogen dioxide can also react with water vapor in the air, resulting in nitric acid (HNO3) another component of acid rain.
- NO2 +H2O –> HNO3
So, a vehicle’s emissions of hydrocarbons, carbon oxides, and nitric oxides react with sunlight and oxygen to form the primary components of atmospheric smog: ozone, nitric oxides, organic compounds, carbon dioxide, and water vapor.
- Hydrocarbon + Sunlight + O2 + CO + NOx –> O3 + NOx + Organic Compounds + CO2 + H2O