Since 1988, the EPA has been progressively reducing the allowable limits for the two main pollutants in heavy duty diesel vehicles: nitrogen oxides and particulate matter. The permitted limits for these pollutants have become more stringent with the introduction of each new EPA legislation.
Nitrogen Oxide Emissions
Nitrogen oxide emissions include nitric oxide (NO) and nitrogen dioxide (NO2). Nitric oxide (NO) is a colorless and odorless greenhouse gas, while nitrogen dioxide (NO2) is a highly toxic greenhouse gas.
Nitrogen oxides can contribute to acid rain and global warming. They are highly active ozone precursors and play an important role in smog formation. At high levels, ground level ozone can disrupt photosynthesis in plants, causing damage to plants and ecosystems. It can also lead to allergy and respiratory problems.
Nitrogen oxides are emitted to the environment via a number of sources. The impact on human health and the environment of nitrogen oxides derived directly from vehicle emissions is an area of ongoing research.
The primary constituents in diesel particulate matter are soot, organic particulates, and sulfates. These particles can come in a wide range of sizes.
Human health can be negatively affected by particulates‹especially by fine particulates that can be carried deep into the lungs. Possible health problems include respiratory disease, heart disease, and cancer.
Particulates are emitted to the environment via a number of sources. The impact on human health and the environment of particulates derived directly from vehicle emissions is an area of ongoing research.