Environmental Impact Assessment: Air Quality, Modelling and Monitoring

An environmental impact assessment examines how a proposed project could affect the surrounding environment.

For industrial projects, the air quality assessment helps answer a practical question: could emissions from the project create unacceptable impacts, and what should be done to prevent or reduce them?

Answering that question requires more than a list of pollutants. The assessment must connect emissions, existing air quality, meteorology, dispersion modelling and applicable regulatory criteria to decisions about project design and operation.

This guide explains the main steps, the information they require and where specialist air quality expertise can make a material difference.

Identify emissions and operating scenarios to start your environmental impact assessment

Start by establishing what the facility could release into the atmosphere and under which conditions. Depending on the project, the emissions inventory may include:

• Combustion emissions such as sulphur dioxide (SO₂), nitrogen oxides (NOₓ) and particulate matter.
• Process emissions, including hydrogen sulphide (H₂S), volatile organic compounds (VOCs) and other substances specific to the operation.
• Fugitive emissions from equipment, storage and material handling.
• Construction dust, vehicle emissions and other temporary sources.
• Flaring, emergency releases, start-up, shutdown and other relevant non-routine operating conditions.
• Greenhouse gas emissions where required by the assessment scope.

Emission estimates commonly come from equipment specifications, process information and data supplied by the client. For some sources, the Alberta emissions inventory may provide relevant information for the specific source or comparable facilities. Data from similar sources can help fill gaps, provided the differences and assumptions are evaluated carefully.

EIAs for facilities like this

The important question is whether the inventory represents the operating scenarios that matter. A routine operating case may tell only part of the story when emergency flaring, equipment outages or changing process conditions could produce higher short-term emissions.

Before modelling begins, confirm: Are the emission rates, gas compositions, source dimensions and operating durations supported by suitable data?

At Calvin Consulting, we often receive multiple data sources for the same emission unit, such as database records, equipment specifications, or stack‑testing results. Having more than one source allows us to cross‑check values and assess their reasonableness, ensuring the inputs used in our assessments are both accurate and defensible.

Establish existing air quality

A new project adds emissions to an environment that already has its own sources of pollutants. Existing conditions may reflect other industrial facilities, transportation, natural sources, regional background concentrations and wildfire smoke.

Provincial monitoring networks provide measurements from stations across their territories. Those data can help establish background concentrations, but choosing a suitable dataset requires judgment. A station may be too distant, influenced by different sources or unrepresentative of the conditions around the proposed facility.

Meteorological data matter just as much. Wind speed and direction, atmospheric stability, temperature and other variables affect where emissions travel and how much they disperse. Terrain and land use can further influence local airflow.

In Alberta, regulatory modelling must follow the applicable Air Quality Model Guideline (AQMG). The appropriate data and processing methods depend on the project and the current requirements.

Background concentrations also matter when evaluating cumulative effects. The proposed project's predicted contribution must be interpreted alongside existing conditions and other sources as required by the applicable methodology.

The key question: Do the selected background and meteorological data represent the conditions relevant to the project and its receptors?

An air quality, noise, and climate impact assessment for a clean environment

Predict air quality impacts

Air dispersion modelling estimates how pollutants move from their sources and what concentrations may occur at ground level or other locations of interest.

The model needs reliable inputs, including:

• Emission rates and source characteristics
• Stack height, diameter, exit temperature and exhaust flow where applicable
• Terrain, land use and receptor locations
• Suitable meteorological data
• Relevant operating scenarios and averaging periods

Model selection depends on the problem being assessed and the applicable regulatory guidance. AERMOD is commonly used for many industrial dispersion assessments. More complex terrain, meteorology or long-range transport questions may require a different approach.

The model can help identify where concentrations may be highest, which operating scenarios matter most and whether additional controls or design changes warrant investigation.

Its results are predictions, not guarantees. As one familiar observation about forecasting puts it, nature has the final say. Models represent real processes through mathematical approximations and available data. Their value depends on how well the assessment represents the problem, how assumptions are tested and how uncertainty is handled.

That is why professional judgment matters. A model can produce precise-looking numbers from unsuitable inputs. A defensible environmental impact assessment explains why its methods and assumptions are appropriate.

Why small technical decisions can matter

A flare assessment, for example, may depend on gas composition, release rate, flare geometry, fuel gas and the duration of the release. A change in flow can also change plume rise, so ground-level concentrations may not change in direct proportion to emissions.

Meteorological assumptions can matter just as much. In complex terrain, the representation of local winds may influence the location and magnitude of predicted impacts.

Interpret results against the right criteria

Predicted concentrations have little meaning until they are compared with the appropriate benchmarks.

In Alberta, the provincial Ambient Air Quality Objectives (AAAQO) and Guidelines (AAAQG) are important references for evaluating ambient impacts. The applicable objective depends on the pollutant, averaging period and required statistical form. The current requirements should be confirmed for each assessment.

Ambient air quality objectives and occupational exposure limits serve different purposes:

• Ambient criteria are used to evaluate air quality beyond the facility and potential impacts on the general public and environment.
• Occupational exposure limits address worker exposure in the workplace under Alberta's Occupational Health and Safety (OHS) framework.

A result that is acceptable under one framework cannot automatically be treated as acceptable under the other. Near a vent, flare or process platform, the relevant assessment may need to consider worker exposure as well as ambient air quality.

Predicted concentrations and deposition rates may also inform subsequent human health or ecological evaluations. Those evaluations can require additional expertise and evidence beyond dispersion modelling itself.

The interpretation must account for background concentrations and cumulative effects where required. A project may contribute only part of the total concentration at a receptor, yet that contribution can still matter when existing air quality is already elevated.

Current Alberta references include the AAAQO/AAAQG, the AQMG and the associated guidance for interpreting regulatory modelling assessments.

The decision to support: Do the results demonstrate compliance with applicable criteria, and are there locations or scenarios that require further analysis or mitigation?

Choose mitigation and understand residual impacts

When an assessment identifies a potential concern, the next step is to determine what can reasonably reduce it.

Options depend on the source and pollutant. They may include:

• process changes,
• lower-emission equipment,
• improved combustion,
• flare modifications,
• vapour recovery,
• leak detection and repair,
• dust suppression or
• restrictions

...on particular operating conditions.

The best option is the one that addresses the identified problem while remaining technically feasible and consistent with applicable requirements. A control measure should be evaluated using appropriate evidence, such as equipment performance data, source testing, monitoring or revised dispersion modelling.

Even effective mitigation leaves uncertainty and may leave residual impacts. Background pollution persists, control systems have operating limits and unusual meteorological conditions can produce concentrations that differ from typical predictions. Start-up, shutdown and emergency conditions may also require separate consideration.

Nice and clean

A sound assessment identifies these limitations and explains how remaining risks will be managed.

Example: evaluating a sour-gas facility

For one Alberta sour-gas facility, Calvin Consulting assessed routine emissions alongside emergency flaring and blowdown scenarios. The analysis considered pollutants including SO₂, H₂S and NO₂ and compared predicted concentrations with applicable AAAQO.

The engineering information was important to the outcome. Release rates, gas composition, operating duration and proposed equipment changes all influenced the scenarios being assessed. Modelling then helped determine whether the proposed cases met the relevant criteria and whether changes to the operating or engineering design warranted consideration.

In one assessment, the predicted concentrations for the evaluated flaring scenarios complied with the applicable objectives. That finding supported the assessment of the proposed operating conditions; it did not guarantee the same result for every possible event.

This is the practical purpose of modelling: to connect engineering information with an environmental decision before that decision is made.

Plan monitoring and follow-up

Monitoring can establish actual conditions, identify trends and help evaluate whether mitigation is working. It may also provide information that improves future assessments.

A monitoring program should have a defined purpose. Depending on the project, that may involve measuring a particular pollutant near a source, assessing conditions in a nearby community, establishing regional background or investigating a specific operating event.

The choice of location, pollutants, instruments and monitoring duration should follow the assessment objectives and applicable requirements. Trigger levels and response procedures may be appropriate where monitoring is intended to support operational management.

In Alberta, the Air Monitoring Directive sets requirements for applicable air quality monitoring and reporting programs. Its current provisions and any project-specific approval conditions should be checked when designing the program.

Monitoring and modelling provide different kinds of evidence. Modelling estimates concentrations for specified scenarios; monitoring records conditions at particular places and times. Comparing the two can be informative, provided the differences in location, timing and conditions are considered.

Need an air quality assessment you can defend?

An environmental impact assessment needs a clear line of reasoning from source data to predicted impacts and from predicted impacts to practical decisions. That requires appropriate methods, reliable inputs and the judgment to recognize when an assumption needs further investigation.

Calvin Consulting Group Ltd. helps industrial clients assess air emissions, conduct dispersion modelling and interpret results for regulatory and operational decisions. Our work includes industrial facility assessments, sour-gas flaring and blowdown scenarios and other situations where the details of the emissions and release conditions matter.

A defensible assessment can help identify problems before they become expensive, focus engineering effort where it matters and provide a clear technical basis for discussions with regulators.

Contact Calvin Consulting Group Ltd. to discuss the air quality component of your environmental impact assessment. Provide the project location, facility type, proposed operating conditions and any existing emissions or modelling information. We can help identify the assessment requirements, the data gaps and the work needed to reach a defensible conclusion.

There are thousands of pages in most of environmental impact assessments I have worked on.  For help with the air quality portion of your company's assessment, please email Barry J. Lough at Calvin Consulting Group Ltd. right here:

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A practical checklist for project proponents

Before submitting an air quality assessment, ask:

• Have the important emission sources and operating scenarios been identified?
• Are emission rates based on reliable data or clearly documented estimates?
• Are the background air quality and meteorological data suitable for the site?
• Is the modelling approach appropriate for the terrain, sources and regulatory requirements?
• Have the correct criteria, averaging periods and statistical forms been applied?
• Have cumulative effects been considered where required?
• Are material uncertainties and limitations explained?
• Have practical mitigation options been evaluated where necessary?
• Are monitoring and follow-up measures appropriate to the remaining risks?

Unresolved questions at this stage can lead to additional modelling, redesign, regulatory questions or delays. Identifying them early is usually more efficient than discovering them after an application has been submitted.

Do you have concerns about air pollution in your area??

Perhaps modelling air pollution will provide the answers to your question.

That is what I do on a full-time basis.  Find out if it is necessary for your project.

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