Pollution Offsets

For air pollutants of regional concern, such as the acid-forming gases of sulfur dioxide (SO2) and nitrous oxides (NOx), air quality depends more upon the net amount of a pollutant emitted within a region than on the specific quantity coming from an individual source. For pollutants of global concern, such as those that contribute to global warming, including methane (CH4), carbon dioxide (CO2), and other gases, the global emissions matter more than the local emissions. Within watersheds, key pollutants such as biological oxygen demand (BOD) or total phosphorus (TP) affect overall water quality. A unique approach to limiting the net quantities of specific pollutants in air and water is discussed in this article.

A variety of pollution control technologies exist for reducing the amount of pollutants released into air. Within the United States, industry-specific standards are established for the maximum achievable control technology (MACT). But sometimes current technology is not adequate at removing a specific pollutant, from a specific source, down to an acceptable level. When this occurs for a pollutant of regional or global concern, an equal or greater reduction in the emissions of the same pollutant from a different source, known as a pollution offset, may be an acceptable alternative for compliance with emissions standards. Offsets may also be bought by organizations or individuals interested in reducing their carbon footprint. To ensure that the actual pollution reduction occurred, third-party verification of the offset is required by all reputable offset registries.

One of the most common types of offsets available for sale or trade is a carbon offset. Carbon offsets are typically quantified in units of metric tons of carbon dioxide equivalents (CO2e). Other global warming gases may be included in carbon dioxide equivalents, such as methane, but their quantities are converted to the equivalent amount of carbon dioxide that possesses a similar potential to cause global warming. Offsets may be sold on the open market, through existing trading platforms. Offsets may also be traded and sold directly between two parties.

Offsets may be traded or sold as means of meeting emissions commitments made by signatory members of the Kyoto Protocol. The United Nations’ Clean Development Mechanism (CDM) verifies projects to ensure that the actual emission reductions occurred and requires that the projects be “additional” to normal modes of operation.

Carbon offset projects must reduce the amount of carbon dioxide, or other global warming gases, released or present in the atmosphere. A wide variety of projects may qualify for carbon offsets, some examples of which are as follows:

• The replacement of fossil fuels with noncarbon-emitting energy sources, such as wind, solar, and hydropower
• The capture and use or destruction of methane generated by the following sources, among others:
  • Municipal wastewater treatment
  • Landfill component decomposition
  • Oil and coal extraction
• The sequestration of carbon by planting trees, which utilize carbon dioxide from the air to produce biomass
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• The utilization of carbon neutral fuels. Fossil fuels take carbon that is sequestered underground and release it into the air when burned, increasing the net amount of atmospheric carbon dioxide. In contrast, burning biomass for power or heat is considered carbon neutral because biomass, such as trees, sequesters carbon from the atmosphere as it grows and releases carbon dioxide back into the atmosphere when it is burned.

These are just a few among the many projects that can create carbon offsets to help reduce the net global emissions of global warming gases.

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