Odour Impacts and Management

An odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans perceive by the sense of olfaction. Odours or smells are both pleasant and unpleasant. While the terms fragrance, scent, aroma and perfume are used primarily by the cosmetic industry to describe a pleasant odor, malodor, stench, reek etc. signifies bad odours.

Odour-free air contains no odorous chemicals. Fresh air is usually perceived as being air that contains no chemicals or contaminants that could cause harm, or air that smells 'clean'. Fresh air may contain some odour, but these odours will usually be pleasant in character or below the human detection limit.

The source of odours can be indoor or outdoor. The indoor odour of cooking processes may be pleasurable while cooking but not necessarily after the meal. Outdoor sources of odors are from sources where recipients have no control. Odor is a very complex matter to quantify and qualify. It varies from person to person what is considered smelly. As most samples of odorous air contain a cocktail of smelly substances with each different odour thresholds, it is nearly impossible to have an on-line analyzer or measuring system which can quantify and differentiate between these components.

The main concern with odour is its ability to cause an effect that could be considered 'objectionable' or 'offensive' depending on the frequency, intensity, duration, location and offensiveness. While odor feelings are very personal perceptions, individual reactions are related to gender, age, state of health and sensitivity in addition to meteorological conditions like prevailing wind direction and speed.

The offensive odour is usually caused by high concentrations of sources and may also be causing direct health effects such as skin, eye or nose irritation. Repeated or prolonged exposure to odour can lead to a high level of annoyance, and the receiver may become particularly sensitive to the presence of the odour.

Odour impacts that have been reported by people include nausea, headaches, respiratory problems, retching, difficulty in breathing, frustration, annoyance, depression, stress, tearfulness, reduced appetite, sleeplessness and embarrassing behaviour. All of these contribute to a reduced quality of life for the individuals who are exposed to odours. The brain function study found neuro-physicological abnormalities such as slower reaction times, color discrimination and mood alterations.

Unpleasant odors can arise from specific industrial processes, adversely affecting workers and even residents downwind of the industry. The most common sources of industrial odour arise from sewage treatment plants, refineries, specific animal rendering plants and industries processing chemicals which have odorous characteristics. For example, rotten food smells nasty and when toxic substances such as hydrogen sulphide are present, it smells like rotten eggs. Many foul smells are formed by dead and decaying matter and during the process of decay the organic material breaks down into other volatile, compounds giving rise to the smell.

People can develop physiological effects from odour even when their exposure is much lower than that typically required to cause direct health effects. This effect is sometimes termed 'odour worry' and is due to the perception that 'if there is a smell- it must be doing physical harm'.

The solution to odour control is through chemical masking and neutralizing products. Masking is the concept behind air fresheners in that a pleasant smell is introduced in high concentrations to mask the unpleasant smell. Neutralization is the process that nullifies the odour-producing chemical, including those persistently produced.

Individually people can avoid odours by closing windows and openings, being less in outdoor air, altering household setting having bedrooms away from odor sources, optimally going out of odour zone, using natural air fresheners, having more indoor and outdoor plantation etc.