Fine particles can be a by product of fossil fuel combustion, such as diesel and bus engines. Fine particles can easily reach remote lung areas, and their presence in the lungs is linked to serious respiratory ailments such as asthma, chronic bronchitis and aggravated coughing. Exposure to these particles may aggravate other medical conditions such as heart disease and emphysema and may cause premature death. Ozone is a chemically unstable molecule composed of three oxygen atoms. Ground level ozone is formed by sunlight and heat acting upon fuel combustion by products such as nitrogen oxides and hydrocarbons.
Ozone occurs naturally in the upper atmosphere and shields the Earth from ultraviolet radiation.
In urban areas, at least half of the ozone producing components come from transportation sources such as automobiles. Because ozone formation is directly related to atmospheric temperatures, problematic ozone levels occur most frequently on hot summer afternoons. Ozone exposure is linked to respiratory illnesses such as asthma and lung inflammation. Extended ozone exposure can exacerbate existing respiratory ailments such as chronic bronchitis and emphysema. Ozone pollution can severely damage vegetation including agricultural crops and forest habitats.