Breaking Down Air Pollution

Photo: The Denver Post

Have you ever been curious about what pollutants are measured when your vehicle is on the treadmill during the emissions inspection? Take a look at the Vehicle Inspection Report provided at the end of the inspection, and you’ll see that they are carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx). But why?

It’s all about your health. Both CO and NOx are pollutants that have been demonstrated to be harmful to your health and the environment – so much so that there are federal health-based standards for them. Hydrocarbons (as well as NOx) are two of the primary components that lead to ground-level ozone pollution – another pollutant with a federal health-based standard. What follows is a little info about each pollutant.

Carbon Monoxide (CO) – Carbon monoxide is a colorless, odorless gas emitted when fuel is burned (this is called combustion). It reduces the body’s ability to deliver oxygen to organs and tissues.


  • Motor vehicle exhaust (accounts for about 50 percent of CO nationwide)
  • Non-road vehicles

Health Effects Include:

  • Chest pain
  • Fatigue
  • Impaired coordination and vision
  • Confusion, dizziness and nausea
  • Reduced oxygen delivery to the body’s organs and tissues
  • Aggravation of heart disease

Ozone – The naturally-occurring ozone layer in the upper atmosphere protects us from the sun’s ultraviolet rays. However, ozone at ground level is a pollutant.

Sources: Ozone is not emitted directly from a source like other pollutants, but forms as a secondary pollutant. Certain “precursor” pollutants like hydrocarbons and nitrogen oxides react chemically in sunlight to form ozone.


  • Motor Vehicles
  • Oil and Gas Exploration and Production Activities
  • Utilities
  • Industrial Activities
  • Paints, Solvents, Degreasing Agents and Cleaning Fluids

Health Effects Include:

  • Chest pain                       
  • Throat irritation
  • Coughing
  • Congestion
  • Aggravation of lung diseases like asthma
  • Decreased lung function

Oxides of Nitrogen (NOx) – Nitrogen oxides are a group of highly-reactive gases formed when nitrogen and oxygen in the air are combined in high-temperature combustion. Nitrogen dioxide is the component of greatest concern because it forms quickly from emissions from cars, trucks, buses, off-road equipment and power plants.


  • On- and Off-road Vehicles
  • Combustion Sources (power plants, oil and gas activities)
  • Aircraft

Health Effects Include:

  • Throat Irritation
  • Respiratory Distress
  • Aggravation of heart and lung diseases

The quality of our air has a direct impact upon our health. Educating ourselves about the most common pollutants, their sources, their effects and what strategies are being used to reduce them is an important part of the effort to improve public health and the environment.

To learn more about air pollution, visit the Colorado Air Pollution Control Division’s websites at and

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