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The Essentials of Air Pollution Modeling

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In the environmental impact assessment, air quality consultants use a model to forecast air quality in the area around the new plant.  An EIA for a new industrial project usually consists of three cases.

You'd expect a research document of this sort to start with historical air quality observations.  Models use this data to define background pollution and establish ambient air quality.  Afterward, we parameterize the emissions of the new sources and run a second model with them.  

Planned Development Case Assessment includes all emissions counted in the second case plus any other proposed projects within the air pollution modeling domain.  Researchers could compare impact comparisons even more meaningfully if they included only the project emissions in the fourth case, which is rare but would please researchers.

The results of these air pollution modeling cases can be interpreted in a few ways. One is to compare the predicted absolute air quality concentrations with the relevant ambient air quality standards. Another interpretation method is to compare each case result with the preceding one and calculate the increments in the maximum predicted concentration as a percentage change.

Assessment of Air Quality: A Summary of Air pollution modeling

Characterization of Sources

Usually, this step of air pollution modeling looks at estimating and identifying stationary sources of:

• Sulphur Dioxide (SO₂),
• Nitrogen Dioxide (NO₂),
• Carbon Monoxide (CO),
• Particulate Matter (PM₂₀ or PM₁₀),
• Polycyclic Aromatic Hydrocarbons (PAH) and
• Volatile Organic Compounds (VOC)

...as industrial development generally increases these emissions.

Data pertaining to the exhaust stack is used to characterize emission sources.  The stack's diameter and height as well as its position in relation to nearby buildings, whose length, height, and width are also needed.  This step also involves figuring out the velocity and temperature of each emission flow.  This step also involves figuring out the velocity and temperature of each emission flow.  For air pollution modeling to work, the mass emission rate for each substance considered must be specified, typically in grams per second.

Fugitive emissions - - multiple simultaneous small leaks that can't be modeled individually - may contain contaminants.    This list often includes VOCs, CO, and hydrogen sulfide (H₂S).

Characterization of the Region

A refined air pollution modeling study needs terrain elevations.  Shuttle data (SRTM) and digital elevation models (DEM) are great sources of elevation data.  Air dispersion models can use data with a horizontal resolution of 100 m or better (i.e., less).  

Once the vegetation cover and land use information is encoded in the right formats, the model gets representative surface characterization parameters.  Depending on the model, this data may include leaf area index (LAI), albedo, and surface roughness.  Modelled dispersion and deposition are affected by the inputs, and they change with the seasons.

Meteorological modeling

Met-Data is also known as weather data.  Advanced air quality models like CALPUFF and CALMET predict temperature, wind, and turbulence fields spatially and temporally.  CALMET inputs selected from mesoscale meteorological models like MM5 should contain the needed wind and temperature profile information for CALPUFF to work.

Using this approach, you can integrate the model data with observed meteorological data.  When used to prepare five years of high-resolution weather data for CALPUFF, it works great.

Why CALPUFF?

Air quality impact assessments use this model to determine changes in ambient air quality.  It's widely available, but you have to learn how to use it before you can run any reliable models.  It's easy to get model documentation and source code.

Joe Scire, the distributor and developer of this and other air quality dispersion models, has a website called src.com.  In applications for new developments that might affect air quality, an ever-growing number of regulatory bodies and jurisdictions accept and even require CALPUFF modelling.

The Air pollution modeling Domain

When an EIA is required for a major project, air quality modeling might be justified for covering a variety of horizontal extents and densities.  Regional Study Areas (RSAs) are usually square or squarish, 100 to 400 km across, with a resolution of one or two kilometres.  Then there's a Local Study Area (LSA), usually square, with a density of 1 km out to 50 km.  There would be several smaller square grids with resolutions of 500 m, 250 m, 50 m, and even 20 m, each big enough to accommodate a few hundred or thousands of grid points.

CALPUFF run-time can be an issue for these projects, and it's roughly proportional to how many grid points are selected.  You could use another model like AERMOD instead.

An EIA could have 15,000 to 20,000 grid points, including dozens or hundreds of special receptors.  There's also a list of special air pollution modeling receptors like towns, hospitals, campgrounds, wildlife reserves, etc.

Model output

For all receptors specified, the model predicts mass per unit volume concentrations.  We can program it to give us one-hour, 24-hour, or annual concentrations, or any other averaging period we want.

A map of the area being examined is superimposed with contours of maximum (or some specified percentile) concentrations for each receptor.  In tabular format, the results for the special receptors mentioned above, commonly known as sensitive receptors, can be compared individually.  By using a map to show maximum predicted concentrations, you can see how things like hills and prevailing wind directions can affect the resulting concentrations.

A model can help decision-makers choose the conditions under which a new development should operate if done right.  It'd let industrial development happen without endangering the environment or public health.  It's a win-win for everyone.

Check out what Calvin Consulting Group Ltd. (Calgary, Alberta) can do if you need air dispersion modeling consultants for your industrial site. 

For more info, contact Calvin Consulting's air pollution and regulatory compliance experts.  Call 403-547-7557 and ask for Barry.  

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Environmental research projects will often include air quality modelling.  

What does this mean?  Find out what the models get used for and how scientists and regulators interpret the results. 

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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Thank you to my research and writing assistants, ChatGPT and WordTune, as well as Wombo for the images.