Refuse-handlers and many industries release unpleasant odors into the air which can travel for miles. Odors inside factories can also make it difficult for people to work, and pollutants can impart a strong odor to water.

Odors can be released from chemicals, chemical reactions, fires, or rotting material. The air carries odor-producing gas molecules, and they are detected by breathing or sniffing. The molecules stimulate receptor cells in the nose, which in turn send nerve impulses to the brain where they are processed into information about the odor.

Research is being performed to quantify and characterize odors. Tests such as sniff chromatography, emission rate measurement, and hedonics are being used in an effort to develop a better definition of what offensive odors are.

Scientists have found that the perception of odors is highly subjective. What one person might not like, another person might not be able...