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Landfill Odors and Emissions

Questions and answers about landfills and associated gases and odors.

Landfill gas is a mixture of hundreds of different gases. By volume, landfill gas typically contains 45 to 60 percent methane and 40 to 60 percent carbon dioxide. Landfill gas also includes small amounts of nitrogen, oxygen, ammonia, sulfides, hydrogen, carbon monoxide, and non-methane organic compounds.

Hydrogen sulfide, dimethyl sulfide, and mercaptans are naturally occurring gases that give the landfill gas mixture its rotten-egg odor . These gases produce a very strong rotten-egg smell—even at very low concentrations or may smell like natural gas. Of these three chemicals, hydrogen sulfide is emitted from landfills at the highest rates and concentrations. Hydrogen sulfide and other sulfur-based chemicals can be smelled at much lower concentrations than concentrations at which adverse health effects may occur. Odorous levels are not necessarily harmful levels.

Ammonia is another odorous gas that is produced by the decomposition of organic matter in a landfill. Ammonia is common in the environment and an important compound for maintaining plant and animal life. People are exposed daily to low levels of ammonia in the environment from the natural breakdown of manure and dead plants and animals. Humans are much less sensitive to the odor of ammonia than they are to sulfur-based chemical odors.

Some non-methane organic compounds (NMOCs), such as vinyl chloride and hydrocarbons, may also cause odors. In general, however, NMOCs are emitted at very low (trace) concentrations and are unlikely to pose a severe odor problem.

The levels of gases that migrate from a landfill and to which people are exposed are dependent on many factors. Systems for collecting and controlling landfill gas have the greatest impact on gas migration and exposures. If a collection or control system is in place and operating properly, migration and exposures should be minimal and no adverse health effects are expected if exposure occurs.

Landfill Gas Primer