Odour impact assessment
James A. Nicell, PhD, PEng (Professor)
Department of Civil Engineering and Applied Mechanics
Of the various categories of air pollutants, odours have been ranked as the major generators of public complaints to regulatory agencies in North American communities. These complaints originate as a result of a wide variety of industries and operations including agriculture, sewage treatment works, paint, plastics, resin and chemical manufacturers, refining operations, rendering plants, pulp mills and landfills, among others.
In communities exposed to odorous emissions, even though there may be no apparent diseases or infirmities, there certainly is not an atmosphere of complete mental, social, or physical well-being. It is recognized that prolonged exposure to foul odours usually generates undesirable reactions in people. These reactions can vary from emotional stresses such as unease, discomfort, irritation or depression to physical symptoms, including sensory irritations, headaches, respiratory problems, nausea, or vomiting. Sub-irritant levels of odorants may trigger acute symptoms through non-toxicological, odour-related mechanisms. These mechanisms have been postulated to include innate odour aversions, odour exacerbation of underlying conditions, odour-related aversive conditioning, stress-induced illness, and mass psychogenic illness.
Odour problems occur with sufficient frequency and sufficient impact to warrant intervention. As such, regulatory agencies and industries are often expected to deal with community odour problems. However, to date they have no truly objective strategies for assessing the impacts of odorous emissions on populations. The lack of such methods prevents authorities from establishing standards which would eliminate, or at least minimize, community odour nuisances. In addition, the offending industries lack a methodology to aid them in predicting their potential impact and for testing odour reduction technologies prior to full-scale implementation.
Even though it is possible to use measurements based on the dilution-to-threshold principle as indicators of potential odour impacts on communities, there are some doubts about the validity of their use. For example, the measurement of a threshold fails to provide any information related to the impact of an odorous stimulus on a neighbourhood in terms of complaint potentials or degrees of annoyance. In addition, detection threshold measurements fail to take into account the potency or the persistence of certain odours. That is, with large changes in concentrations, some odours are accompanied by relatively small differences in perceived odour magnitude. These variables are the extremely important dimensions for quantifying an odour nuisance in a locality.
Therefore, current research is focusing on the development of a new odour impact assessment method that combines dose-response relationships for odours with improved dispersion modelling techniques. This method will provide a better basis for odour impact assessment by incorporating the effects of odour concentration, volumetric emission rate, odour offensiveness and persistence, community and source characteristics, and meteorological conditions into estimates of the impact on a community.
Using the proposed method, the severity of the impacts from different sources in a neighbourhood can be assessed and ranked. Subsequent analyses can provide regulatory agencies and plant personnel with a basis for prioritizing their approach to resolving impacts originating from odour sources. The proposed methodology is of practical significance to any facility which produces or has the potential to produce odours. The method can be used by industries who are considering the implementation of various process changes, feedstock changes, or emissions control technologies to reduce odorous emissions. In many cases, the effectiveness of these strategies in reducing odour impact is not usually known until after they have been implemented at the full scale. However, through use of the proposed procedure, industries will be able to collect data from pilot plant studies and apply the odour impact assessment procedure to predict the odour impact on a surrounding community. The procedure will facilitate the choice of the most effective approach to reducing odour impact before implementation at the full scale. This can translate into monetary savings and improved relations with surrounding populations by allowing industries to quickly resolve conflicts concerning odour impact and by avoiding the implementation of ineffective odour control strategies. In order to assist the practitioner with this process of assessment, a software tool called OdorCalc has been developed (see figure).
Examples of graduate theses
Gorgy, Tamer Alexan (2003) Validation of an air dispersion model for odour impact assessment.
Ma, Yue (2003) Software development for odour impact assessment.
Sikdar, Anamika (2001). An objective method for the assessment of the impact of odorous emissions from stationary sources. MASc thesis, Dept of Civil & Environmental Engineering, University of Windsor. Co-supervised by P. Henshaw (Windsor).
Tsakaloyannis, Mike (1997). Development of a regulatory strategy for odour impact assessment. MEng thesis, Dept. of Civil Engineering and Applied Mechanics, McGill University.