Assessing Odour Compliance

Industrial odours are regulated provincially in Ontario under the Ontario Environmental Protection Act (R.S.O., 1990, Ch. E19). Section 14 (1) states that “… no person shall discharge a contaminant or cause or permit the discharge of a contaminant (including odour) into the natural environment that causes or is likely to cause an adverse effect (complaint).”

The Ministry of the Environment (MOE) has established an odour impingement guideline that is used to assess existing and proposed plant emissions for the likelihood of causing an adverse effect. Currently, the guideline value is 1 (ou/m3) which represents the odour concentration at which 50% of the population would be able to detect odour in the air.

Analysis of industrial odours is facilitated by extracting and collecting gaseous samples from the source and then presenting the samples to trained assessors called odour panelists who “sniff” the samples and report whether they can detect an odour.

A dynamic dilution olfactometer is used at Pinchin to dilute the odorous samples with odour free air to sub-detection levels (i.e. below the detection level of all assessors). Sequentially, each panelist is presented with three samples, one containing the diluted odour sample and two that are odour free. Panellists are asked to state, which of the three sample presentations was different, by recording a Guess, Detect, or Recognize response. The concentration of odour in the next set of three presentations is doubled and re-presented to each of the panelists where they are once again asked to record their Guess, Detect or Recognize response. The presentation sequence of doubling the odour concentration is repeated until each of the panelists has detected the odour. Statistically, the dilution at which 50% of the panelist respond with a Detect is known as the odour threshold value (OTV). This statistical approach is known as triangular forced-choice ascending concentration method.

OTV can be considered as the odour concentration of an emission source. Generally, high OTV sources require enhanced atmospheric dilution, or possibly emission control, to prevent adverse effects.

Prediction of off-property or neighbourhood odour impact is accomplished using atmospheric dispersion models such as SCREEN3, ISCST3, or AERMOD. These models use emission source specific information such as discharge rates, exhaust height, distance to buildings and property lines, and meteorological data, to predict the amount of dilution that can be expected before the odorous sample impacts the ground. Comparison of the maximum predicted impact value to the odour guideline establishes compliance.

Once the assessment and modelling is complete, a wide range of control options exist if the source is not in compliance. Once the control is implemented, a re-assessment must be performed to demonstrate compliance.