Understand the role and operation of atmospheric emission dispersion studies
Atmospheric emissions are an integral part of industrial, mining, municipal, and even agricultural activities. To ensure they do not compromise public health or the environment, the MELCCFP often requires their implementation of’Atmospheric dispersion study.
What is an Atmospheric dispersion study ?
An atmospheric dispersion study aims to predict how contaminants emitted into the air will disperse in the environment, and then to estimate the expected concentrations in places where people live, work, or travel. According to the Guide de la modélisation de la dispersion atmosphérique du MELCCFP (2025), these studies are essential to avoid the degradation of air quality and to verify compliance with Quebec standards for environmental permit applications.
In other words, they allow us to answer the following question:
« What happens to contaminants after they are released into the atmosphere? »
Atmospheric dispersion studies are necessary for what?
Dispersion studies are used to:
Assess environmental impacts before a project
The MELCCFP uses the Atmospheric emission dispersion modeling to authorize projects that could emit contaminants. The results must demonstrate that air concentrations remain below the standards Règlement sur l’assainissement de l’atmosphère (RAA).
Optimize the design or operation of a facility
The Atmospheric dispersion study allow, among other things:
- To adjust the height of a chimney;
- To correct emission rates;
- To add filters or other mitigation measures.
GCM Enviro Synergies Use these results to recommend practical solutions for improving compliance and facilitating the obtaining of ministerial authorization.
Protecting public health and ecosystems
The Atmospheric quality standards are designed to limit health risks and environmental nuisances. Dispersion studies make it possible to quantify the impacts of atmospheric emissions on the environment and to implement measures to mitigate them.
How is an atmospheric dispersion study conducted?
A comprehensive study follows several standardized steps, framed by the guide of MELCCFP.
Quantify emission sources
Several data points can be used to quantify these atmospheric emissions, such as:
- Emission factors (AP-42, material balances);
- The technical specifications of the equipment;
- The nature of the contaminants;
- Operating conditions.
Choose a dispersion model
The MELCCFP recommends AERMOD or AERSCREEN models, used in North America to simulate dispersion according to:
- Topography;
- The weather conditions;
- The characteristics of the sources (height, temperature, velocity).
AERMOD is the one that is most commonly used. GCM Enviro Synergies Use this template.
Use representative weather data
Studies often require wind, temperature, and atmospheric stability data, sometimes provided directly by the MELCCFP for AERMOD.
Simulate different scenarios
The models incorporate:
- Normal operating conditions;
- The worst dispersion conditions;
- Seasonal variations;
- Emergency situations (exceptional episodes).
Interpret ground concentrations
The results show where, when, and at what concentrations contaminants reach sensitive receptors such as:
- Residential neighborhoods;
- Schools and hospitals;
- Wetlands and sensitive habitats.
AnAtmospheric dispersion study must then be submitted to the MELCCFP for review.
A more responsible industry
Companies can identify the best technologies to reduce their environmental impact. By predicting pollution levels even before a project is built, they can prevent air quality standards from being exceeded. These studies are often made public as part of the permitting and consultation processes.
Toward more accurate and accessible modeling
According to the guides Last updated in 2025, atmospheric modeling is evolving rapidly:
- The tools are more precise,
- Weather datasets are more comprehensive.,
- Methodologies have improved significantly.
Conclusion
The Atmospheric emission dispersion studies are much more than just regulatory requirements: they are essential scientific tools for protecting our air quality.
By combining modeling, meteorological data, regulatory assessment, and technical expertise, they enable informed and responsible decisions for the environment and public health.
If you are a municipal administrator, a business leader, or an environmental professional, understanding these studies is essential for developing sustainable and compliant projects. GCM Enviro Synergies can assist you with these steps.
Daniel Lapierre, P.Eng., Project Manager - Environmental Studies and Authorizations
References:
Guide de la modélisation de la dispersion atmosphérique
Atmosphere Quality Standards and Criteria
Guide d’application du Règlement sur l’assainissement de l’atmosphère (chapitre Q 2, r 4.1)
Quebec Air Quality Standards and Criteria: Framework for Determination and Enforcement
q-2, r. 4.1 – Règlement sur l’assainissement de l’atmosphère
AP-42: Compilation of Air Emission Factors from Stationary Sources | U.S. EPA