An olfactometer is used to determine the odour concentration of an air sample during olfactometry. The odour concentration is defined through the dilution, which is needed in order to distinguish the diluted odourous air from clean, odourless air, by 50% of a trained and calibrated panel.
An odour immission concentration
The odour emission from the source will result in a certain odour concentration at the surrounding buildings. The concentration of the odour at living height is called the odour immision concentration.
The odourimmission concentration is usually detrmined using dispersion modeling based on the odour emission from the source and the charachteristics of the source (e.g. emission flow rate, location, temperature of the emitted air...)
Odour immision concentrations are expressed as percentile values (98 percentile for 1 se/m³) and are a measure for the impact of an odour source on its environment.
Odour emission (se/s or ouE/s)
Multiplication of the odour concentration (se/m³ or ouE/m³) and the flow rate (m³/s)
The odour threshold distance or maximal odour perceivable distance
The maximal distance downwind of the source where the odour is perceived under specific meteorological conditions.
An odour concentration
Amount of se/m³ (determined through field panel measurements), or the amount of ouE/m³ (determined by olfactometry).
Emission - Immision
Emmision is the discharge of pollutants, which are ejected by the source (e.g. a chimney).
The way in which the contaminated material is then dispersed in the atmosphere will depend on the height of the chimney, the wind direction, the turbulence, the temperature, the nautre of the pollutant, ... The emitted substances are dilluted, dispersed and transported in the environment.
Finaly, the substances dwell on living height (1.5 m above the ground), present in a certain concentration as the immission.
A field panel measurement
A field panel measurement is based on the registration of an odour plume through the observation of an objective and trained panel. Only the typical odour of a certain company is taken into account during the registration of an odour plume, odours from other sources are neglected. Before the start of a field panel measurement, the panel has to get acquainted with the typical odour(s) of the company. The team starts downwind of the source and tries to cross the direction of the wind in perpendicular at different distances. On a topographical map the locations are marked where the odour was perceived. Using this methodology an idea about the size of the impact area as well as the maximal odour threshold distance can be determined.
A sniffing unit
A sniffing unit per cubic meter (se/m³) is by definition the odour concentration in the field at the location where the of the source is just perceived by the field panel measurement, so at the maximal perceivable distance.
The odour emission of the source is given in sniffing untis per time unit (se/s).
A percentile value
The percentage of time a certain average concentration is not exceeded. The fraction of the measured or calculated values which exceed a certain predetermined threshold. During odour impact assessment the 98-percentile of 1 se/m³ is often used, this indicates the area where during 2% of the time (based on 1 year) a concentration of 1 se/m³ or higher is perceived.
An odour unit
One European odour unit per cubic (ouE/m³) is the concentration of an odourous compound which is perceived by an average person. No difference is made depending on the odour type.
The odour emission of the sources is given in odour units per time unit (ouE/s).
An odour control plan
An odour control plan is a combination of an impact analysis and a remediation study. During the impact analysis, the effect of the odour source on the surroundings of the company is estimated (e.g. by field panel measurements). The investigation of the importance of different odour emission points (e.g. through olfactometry) is the first part of the remediation study. The second part contains technical adjustments to reduce the emissions and recommendations on timing of the proposed changes.
An odour control plan has a wide approach and contains:
An odour audit
An odour audit is a 'light' version of an odour control plan. A screening of the company is made based on activities, products and services with emphasis on odour emissions. During the audit, interest goes to environmental-technical, organizational, environmental-hygienic and (mostly) managing aspects. An odour audit has the intention to result in an internal code of good practice for the company with tips and recommendations for managing the odour.
The Code of Good Practices "Determination of odour dispersion through field panel measurements
The odour policy of the Flemish government is based on field panel measurements to quantify odour emissions and immissions. This code of good practices describes the way to perform field panel measurements, the calculation of odour emmisions and the calculation of odour immissions.
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