Where Should You Locate Ambient Air Quality Monitoring Equipment in Alberta?

A practical guide to Alberta's Air Monitoring Directive Chapter 3, including station siting, dispersion modelling, sampling systems and common installation mistakes.

A monitoring station can satisfy Alberta's distance and height requirements yet still be poorly located to measure the air pollution it was intended to monitor.

Suppose dispersion modelling identifies an area of elevated pollutant concentrations near an industrial facility. The location looks promising until a site visit reveals nearby buildings, restricted access or unreliable power. Moving the station solves those problems, but may change what it measures.

How do you select a location that meets Alberta's Air Monitoring Directive (AMD) and produces representative, defensible data?

This guide explains how to evaluate locations for ambient air quality monitoring equipment, apply the main requirements of AMD Chapter 3 and determine whether a complete monitoring installation is suitable.

It includes a siting reference table, lessons from Calvin Consulting's monitoring audits and a practical checklist to use before committing to a location.

Start with the Monitoring Objective

The first question is straightforward: What are you trying to measure?

A monitoring station may be intended to measure:

• Maximum ambient concentrations associated with an industrial operation
• Air quality near a community or other sensitive location
• Background concentrations away from major local sources
• Long-term changes in regional air quality
• Concentrations associated with a particular source or activity
• Compliance with monitoring conditions in an environmental approval

The appropriate location depends on the answer.

For example, the highest predicted concentration from an industrial stack might occur several hundred metres from the facility...A community monitoring station may need to be located farther away, where people live or spend time.

Those two stations answer different questions

A monitoring location can provide technically accurate measurements while remaining poorly representative of the conditions it was intended to characterize.

Before selecting ambient air quality monitoring equipment or establishing a station, define the monitoring objective and the geographic area the measurements should represent.

How Dispersion Modelling Helps Choose a Monitoring Location

Example of passive sampler siting requirements

For industrial projects, air dispersion modelling can be an important part of monitoring site selection.

Models such as AERMOD and CALPUFF use information about emissions, meteorology, terrain and source characteristics to estimate pollutant concentrations at locations surrounding a facility. A modelling assessment can help identify:

• Areas with relatively high predicted concentrations
• Locations affected by particular emission sources
• Differences between short-term and long-term concentration patterns
• Potential contributions from nearby industrial operations
• Areas where monitoring would provide useful information

The site-selection requirements in AMD Chapter 3 address the use of dispersion modelling for relevant new industrial facilities, subject to the Director's direction and applicable approval requirements.

However, the highest modelled concentration is not automatically the best location for a permanent monitoring station. The modelling results must be interpreted in relation to the monitoring objective and practical siting conditions.

From model results to an actual location

Consider three possible locations near an industrial facility.

Illustrative comparison. These are hypothetical locations and do not represent an actual project I have worked on.

• A modeller may initially favour Location A because of its predicted concentrations. However, an obstruction could make it unsuitable without adjustments.
• Location B offers convenient access but may be influenced by traffic emissions unrelated to the monitoring objective.
• Location C may have a desirable concentration pattern, although maintaining the station could become expensive.

The final decision requires consideration of all these factors. Professional judgement helps determine which location will provide the most useful data over the life of the monitoring programme.

Alberta AMD Chapter 3: What Are the Siting Requirements?

Alberta's Air Monitoring Directive Chapter 3 is titled Ambient Monitoring Site Selection, Siting Criteria and Sampling System Requirements.

Ambient air quality monitoring equipment rules

The 2016 edition establishes requirements for site selection, continuous ambient analyzers, meteorological instruments, passive samplers, intermittent samplers, precipitation sampling equipment and sampling systems.

It also addresses documentation and regulatory authorization. The following table summarizes important siting considerations.

The governing chapter and its tables must be consulted for complete requirements, exceptions and exact wording.

These requirements provide a technical foundation. They should be applied to the actual ambient air quality monitoring equipment and monitoring purpose rather than treated as a generic checklist.

Continuous ambient air quality monitoring equipment

For a continuous ambient analyzer, nearby objects can alter measured concentrations in several ways. Trees can influence airflow, remove some pollutants from the passing air or contribute localized biological material. Buildings create wind wakes and turbulence. A sample inlet located close to a structure may measure conditions influenced by that structure rather than the intended surrounding atmosphere.

AMD Chapter 3 therefore establishes specific separation and airflow criteria. For continuous sampling inlets, important considerations include:

• More than 20 m horizontal separation from trees
• Separation from airflow obstacles greater than twice their height above the inlet
• An elevation angle no greater than 26.5° from the inlet to the top of an obstacle
• Unrestricted airflow in the required wind quadrants
• Applicable sampling heights and roadway setbacks

Some configurations have specific provisions, so the complete clause and table should be checked.

Understanding the 26.5° obstacle rule

The angle is measured upward from the sample inlet toward the top of a nearby obstruction. It can be calculated using:

Angle = arctan(obstacle height above inlet ÷ horizontal distance)

Suppose the top of a nearby building is 8 m above the sampling inlet and the building is 20 m away. The elevation angle is approximately 21.8°. That would satisfy a 26.5° angular limit. The horizontal separation also exceeds twice the 8 m height difference.

However, meeting these two geometric criteria does not establish that every other siting requirement is satisfied. Nearby trees, airflow restrictions, roads and other conditions must still be considered.

This is why a site survey should document actual measurements rather than relying solely on appearances.

Where Should Wind Instruments Be Installed?

Wind measurements are particularly important for interpreting ambient pollutant concentrations. They help identify whether elevated measurements coincide with winds arriving from an industrial facility, roadway or other source. 

Unfortunately, wind instruments are also sensitive to poor exposure. Buildings, towers and vegetation can distort both wind speed and direction.

AMD Chapter 3, Table 3 establishes siting criteria for wind instruments, including:

• Height greater than 2.5 times the monitoring shelter height, with a minimum of 10 m above ground
• Appropriate clearance above obstacles and uniform exposure within the specified surrounding area
• Alternatively, separation from obstacles greater than ten times obstacle height, as provided in the table
• Orientation of wind direction instruments relative to true north

These requirements need to be interpreted together. A wind sensor mounted 10 m above ground does not automatically satisfy the full siting criteria.

A useful site survey should identify nearby obstacles, their dimensions and their relationship to the proposed sensor.

A lesson from an AMD audit

During a review of ambient monitoring procedures, Calvin Consulting identified an inconsistency involving wind-instrument siting.

An operating procedure described obstacle separation using a distance of twice the obstacle height, while the relevant AMD Table 3 provision specified greater than ten times obstacle height.

The discrepancy demonstrated why operating procedures should be checked against the governing directive. It did not, by itself, establish that the physical instruments had been installed incorrectly.

The lesson is practical: a monitoring programme needs accurate instructions as well as correctly installed equipment.

Passive and Intermittent Sampler Locations

Passive samplers collect pollutants over an extended exposure period without continuously pumping air through an analyzer.

Data collection at precise locations

Intermittent samplers collect samples during defined periods using equipment appropriate to the monitored contaminant.

Both types can provide useful information, particularly when multiple locations are needed to examine spatial differences.

Passive samplers - AMD Chapter 3 includes requirements for diffusion barrier height, obstruction exposure and mounting arrangements.

• The diffusion barrier surface is generally positioned 1.5–4 m above ground, with additional requirements described in Table 4.
• Airflow should reach the sampling surface without inappropriate restriction from nearby structures.
• Replicate samplers also need suitable separation and comparable exposure.

Intermittent samplers - Intermittent sampler siting requirements appear in Table 5.

• They address sampling height, obstruction clearance and airflow conditions.
• The requirements depend on the method and should be reviewed before installation.

Why actual sampling height matters

In another portion of Calvin's AMD audit, a passive sampling procedure described the required diffusion barrier height while elsewhere referring to samplers mounted on much taller towers.

That apparent inconsistency required clarification. A tower's overall height and the height of the sampling element are different measurements. The correct installation information must be established from the monitoring configuration and documented accordingly.

This is a good example of why an audit examines the equipment records and procedures together.

Follow the Alberta air monitoring directive to ensure representative measurements

Precipitation Sampling Equipment

Precipitation chemistry monitoring introduces another set of siting considerations. Rain and snow samples can be influenced by nearby vegetation, surfaces, wind turbulence and contamination from local sources.

Where precipitation collectors share a location with gas analyzers or particulate monitors, the requirements of different equipment types must be considered together. AMD Chapter 3 includes provisions for precipitation sampling equipment addressing:

• Height of the collection opening
• Ground conditions and nearby paved surfaces
• Obstruction exposure
• Snow accumulation
• Equipment orientation and installation
• Power supply and associated precipitation measurements

Background precipitation monitoring has additional criteria intended to reduce unwanted local influences.

For detailed requirements, consult AMD Chapter 3, Section 2.5 and Table 6, together with Chapter 4's precipitation monitoring requirements.

The best location for an ambient gas analyzer may not provide suitable exposure for precipitation chemistry sampling. A combined monitoring station therefore needs a coordinated layout.

Sampling System Integrity: Does the Air Reach the Analyzer Unchanged?

Selecting a suitable location for ambient air quality monitoring equipment is only part of establishing a reliable monitoring system. Air collected at the inlet must reach the analyzer without unacceptable changes in composition or concentration.

Sample tubing, manifolds, pumps, filters and shelter conditions can affect the measurements.

For example, sulphur dioxide can be lost from a sample under certain conditions if condensation occurs in the sample line. Particulate matter can also deposit within tubing, depending on particle characteristics and sampling-system design.

The appropriate materials and arrangements depend on the pollutant and monitoring method. Changes should be evaluated against the applicable technical requirements.

The complete monitoring system should be documented in the Quality Assurance Plan and supporting operating procedures. A well-positioned sampling inlet provides limited value if the sampling system changes the air before it is measured.

How Can You Tell Whether an Existing Monitoring Location Is Still Suitable?

An established monitoring station may deserve a review when the facility changes, new sources appear or the collected data raise questions about representativeness. Useful evaluation methods include:

• Site inspections: Compare current conditions with the original documentation, including photographs, inlet heights and nearby obstructions.
• Wind roses and pollution roses: Examine relationships between pollutant concentrations, wind speed and wind direction to help understand source influences.
• Comparison with nearby stations: Look for concentration patterns that may indicate localized influences or differences in measurement conditions.
• Dispersion modelling: Compare expected concentration patterns with observations, considering the limitations of both the model and the measurements.
• Supplementary monitoring: Passive samplers, mobile measurements or other suitable methods may help investigate spatial differences before relocating a permanent station.

Each method addresses a different part of the problem. An unexpected measurement does not automatically mean the station is poorly located. It may indicate an emission event, instrument problem, meteorological effect or genuine local concentration difference.

An experienced review examines these possibilities before recommending changes.

What Should a Defensible Site Selection Assessment Include?

For an industrial operation establishing a new monitoring station, a documented assessment should explain the reasons for the proposed location.

Depending on project scope and regulatory requirements, useful deliverables may include:

Provide the necessary information for applicable authorization and approval processes

The assessment should provide enough information for another qualified professional or regulator to understand how the location was selected.

How Calvin Consulting Can Help

Calvin Consulting Group Ltd. has experience in air dispersion modelling, meteorological assessment, regulatory air-quality compliance and evaluation of monitoring programmes.

Our work includes interpreting predicted air-quality impacts, assessing monitoring requirements, preparing Quality Assurance Plans and conducting AMD audits. For a proposed or existing monitoring location, Calvin can help:

• Establish the monitoring objective and applicable requirements
• Review facility emissions and nearby sources
• Interpret dispersion modelling results
• Compare potential monitoring locations
• Assess meteorological conditions, terrain and obstructions
• Review AMD siting criteria and supporting documentation
• Identify practical installation and operating constraints
• Recommend further investigation or improvements where needed

A site-selection assessment can help identify technical or regulatory problems before significant investments are made in equipment, buildings, utilities and installation.

It can also help establish whether an existing monitoring location remains suitable as conditions change.

Recommended Official References

The following Alberta government documents provide the governing requirements and supporting guidance.

Regulatory note: This article summarizes key requirements from AMD Chapter 3. The official documents and applicable approval conditions govern. Readers should check for subsequent amendments, written authorizations and other project-specific requirements.

Explore Related Stuff in the Air Articles

These related topics provide additional information about ambient air quality monitoring equipment, meteorology and the science behind air-quality assessments.

These topics are available through the Stuff in the Air sitemap and related technical pages.

Need Help Choosing an Alberta Air Monitoring Location?

The right monitoring site should satisfy Alberta's siting requirements and provide the measurements the monitoring programme actually needs.

Getting that decision right can require dispersion modelling, meteorological interpretation, field measurements, technical documentation and an understanding of the facility's regulatory obligations.

A suitable location can support reliable environmental information for many years. A poorly selected site may require additional investigation, modification or relocation.

Calvin Consulting Group Ltd. can help evaluate the technical and practical suitability of proposed monitoring locations before equipment is purchased or installed.

For assistance with ambient air quality monitoring equipment siting, AMD compliance, dispersion modelling or monitoring programme reviews, contact:

Calvin Consulting Group Ltd.
Calgary, Alberta
403-547-7557

Email:

Bring your monitoring objectives, relevant EPEA approval conditions and any preliminary candidate locations to the discussion. They provide an excellent starting point for a defensible site-selection assessment.

Additional lists for Reference:

These questions ensure that air quality monitoring systems are effective and comply with regulations:

• What is the Air Monitoring Directive (AMD)?
• What's new with AMD amendments?
• Where's the best place to put ambient air quality monitoring equipment?
• Siting criteria for air monitoring equipment?
• What's the deal with continuous ambient air monitoring?
• What's the best place for wind instruments?
• What's the best way to position passive and intermittent samplers?
• Precipitation sampling sites?

Five common air-monitoring siting mistakes

1. Choosing the location before understanding the monitoring objective.

2. Treating the AMD distance requirements as the entire siting exercise.

3. Ignoring nearby sources, roads, buildings or terrain.

4. Selecting a technically compliant site that is impossible to maintain year-round.

5. Assuming the closest available location is the most representative location.

The dangerous part? A monitoring site can satisfy a checklist and still fail to address the real problem.

FOR YOUR CONVENIENCE: Before You Select a Monitoring Site

Ask yourself:

✓ What pollutant am I trying to measure?

✓ Am I measuring maximum impacts or community exposure?

✓ Is this station intended for compliance or trend monitoring?

✓ Will future construction change airflow?

✓ Can technicians safely access it year-round?

✓ Will utilities remain available?

✓ Can calibration gases be transported there?

✓ Will vegetation change over the next decade?

✓ Does the location satisfy both AMD and the monitoring objective?

Need to select a monitoring location?

→ Understand the AMD siting criteria
→ Identify potential locations
→ Use emissions/source information
→ Consider meteorology and terrain
→ Use dispersion modelling where appropriate
→ Evaluate candidate monitoring locations
→ Develop the QAP
→ Implement and audit the monitoring network

A location can satisfy the basic distance requirements and still be a poor monitoring site. We often look beyond the checklist to determine whether the station will actually measure the air quality question the network was designed to answer.

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

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Monitoring Site Pre-Approval Checklist

Before finalizing a monitoring location, verify:

□ Monitoring objective defined (e.g., maximum impact, community exposure, source attribution or background monitoring)
□ What pollutants and averaging periods are relevant?
□ Relevant AMD siting criteria identified
□ Approval requirements reviewed
□ Required regulatory authorization obtained (where applicable)
□ Nearby emission sources mapped
□ Dispersion modelling considered where appropriate
□ Meteorological sensor exposure, orientation and height verified (if applicable)
□ Prevailing wind conditions assessed
□ Terrain reviewed
□ Trees and buildings assessed
□ Potential future obstructions or operational changes considered
□ Roadway influence assessed
□ Sample inlet height confirmed
□ Sampling system design preserves sample integrity (line losses, residence time, contamination, heated lines where required)
□ Obstruction angles/distances checked
□ Power available
□ Communications available
□ Security addressed
□ Year-round access confirmed
□ Snow/ice considerations addressed
□ Generator exhaust considered
□ Landowner/access permissions confirmed
□ QAP implications considered
□ Documentation /photos/site plan prepared

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Five Common Monitoring Site Selection Mistakes

1. Selecting a location before defining the objective - A station installed for convenience may fail to represent the intended industrial impact, community exposure or background conditions. Better approach: Establish what the monitoring programme needs to measure before evaluating locations.
2. Treating minimum setbacks as the entire decision - AMD siting criteria are essential, but they cannot answer every question about representativeness. Better approach: Evaluate the regulatory requirements alongside meteorology, terrain, emission sources and modelling results.
3. Ignoring nearby or changing pollution sources - Traffic, temporary construction, equipment exhaust and future development may introduce unwanted influences. Better approach: Survey nearby sources and consider how the surroundings may change during the station's operating life.
4. Overlooking maintenance and winter conditions - An excellent technical location may become impractical when snow blocks access, power is unreliable or calibration equipment cannot be transported safely. Better approach: Include year-round operation, utilities, communications and site security in the selection process.
5. Failing to review the site after installation - Vegetation grows, structures are added and industrial operations change. Better approach: Conduct periodic site inspections, maintain photographs and review whether the location remains representative of the intended monitoring objective.

These issues can arise even when the original installation was carefully planned.