The invisible assault on our air - How is Air Pollution Caused

How we pollute the air, you ask? I shall demystify Rather than tracking a criminal, you're tracking an invisible foe - air pollution. How is air pollution caused?

Our actions, from driving around to mismanaging dusty roads, can pollute the air in surprising ways. Scientists who model air quality have to deal with tricky culprits, like windblown dust. We're getting closer to understanding this complex issue with advanced tools and clever techniques. Put on your detective hat and we can see a bit about air pollution!

Dust in the WindThe invisible trail of pollution

What's so interesting about this page?

  • It's unusual! We breathe air every day, but how it gets polluted can surprise us.
  • This is relevant! Understanding a bit more about air pollution's sources empowers you.
  • Hopeful! Understanding the challenges and solutions gives you a sense of agency, the ability to devise solutions.

It's part of a series on air quality dispersion modelling that covers the regulations and guidelines provided by each western province. Here's how professional dispersion modellers should handle emissions that don't come from normal smokestacks and chimneys (known as point sources), or flares.

Emission set-ups like this can take the form of a collection of several similar sources or tiny leaks in a facility's infrastructure, or a stack whose design prevents plumes from going straight up.

Keeping British Columbia's Air Clean: Advanced Modelling Techniques

Fugitive sources, like dust from unpaved areas or process changes, are hard to pin down because they're variable and hard to control. These are usually close to the ground and affect nearby areas the most. It's important to identify these sources and any nearby sensitive spots. Their emissions are often estimated based on uncertain factors, like AP-42 guidelines, published by the United States Environmental Protection Agency.

Fugitive Emission MonitoringParticulates in air pollution

AERMOD and CALPUFF, the dispersion models we use most often, can handle these sources, including dust deposition from gravel pits. To gauge their impact and effectiveness, it's common to use ambient monitoring and dispersion modelling together. Modelling results from fugitive sources should be separated from more certain ones, like point sources.

And important answer to how is air pollution caused is stack design.  For instance, when there are horizontal stacks or rain caps on a stack, the effluent doesn't have vertical velocity, but it may still rise due to buoyancy if it's warmer than the air around it.

AERSCREEN and AERMOD can handle this with options like POINTCAP and POINTHOR, which adjust for capped and horizontal plumes. CALPUFF adjusts the vertical momentum flux factor (the extra "ooomph" you get with a fast exit velocity) to manage these sources.

The factor ranges from a perfect 1 for a vertical stack to 0 for a horizontal/capped stack if emissions are constant. CALPUFF's input files also account for changes in emissions over time.

Modelling fugitive emissions and merging plumes in Alberta to address complexity

The plumes from nearby stacks can sometimes merge when emissions come from different sources, enhancing plume rise. Models don't explicitly address this, so treating sources separately is often a conservative approach. However, if similar stacks are close together and their characteristics are similar, they can be treated as one.

Here's a tip from the Alberta modelling guideline: For each stack you can calculate a parameter, M, based on its height, flow rate, temperature, and emission rate:

Plume Merging: When Stacks Team Up

It's assumed that all emissions from merged stacks come from the stack with the lowest M value. All relevant information about merged stacks must be included in the report, and include the combined emission rate for all sources in the model input.

Enhanced plume riseMy thoughts on merging Stack plumes

How is air pollution caused? One common way is fugitive emissions.

It's hard to pinpoint fugitive emissions because they change with wind speed, temperature, and time of day. Trying to estimate their control efficiency adds another layer of uncertainty. Estimates can come from reputable sources like AEIR, CAPP, or AP-42 emission factors when better data isn't available. It's important to choose the right source type, like area or volume sources, and consider seasonal variations if necessary.

In AERSCREEN, AERMOD, and CALPUFF, you can model non-vertical releases and stacks with caps. A point source stack with horizontal stacks or rain caps doesn't have vertical velocity. The plume may still rise, however, if the effluent is warmer than the surrounding air. The exit velocity can even be negative, meaning downward, causing the plume to rise from a lower point than the actual stack exit.

Finding out How is Air Pollution Caused with Multi-source air quality modelling in Saskatchewan

Air quality models need to take into account different types of sources and their characteristics.

For example vehicular dust emission rates are affected by road types, silt loading, and dust suppressants. Modelling emissions from haul roads can be helped by the Haul Road Workgroup Final Report Submission to EPA OAQPS.

Ground-level emissions like those from parking lots or storage piles can have a big impact on air quality. They're hard to characterize because of varying factors like wind speed and temperature. It's important to choose the right source type and take seasonal variations into account when modeling them.

Road and dust suppressantSaskatchewan's air models account for every dust source.

Wind erosion: Emissions from sources like storage piles vary throughout the year depending on wind speed and material moisture. AERMOD can handle variable emissions based on wind speed categories, which is crucial for modelling PM10 exceedances.

Combining individual sources: Sometimes, facilities have lots of small sources. Similar sources can be combined into volume or area sources to simplify modeling. An approach like this requires careful consideration of source characteristics, location, and operating periods.

Emissions from horizontal stacks and capped vertical stacks (with rain caps) usually don't move upwards much at first. Buoyancy, caused by temperature differences, is the main factor in vertical motion. There are even times when the exit velocity from a rain cap stack is downward, causing the plume to start lower than the physical stack height.

These sources need adjustments to minimize momentum effects while keeping buoyant plume calculations accurate. Both AERMOD and AERSCREEN have options (POINTHOR for horizontal and POINTCAP for capped sources). These options keep plume buoyancy when there is minimal vertical momentum. The models adjust for plume rise and downwash based on input stack parameters.

CALPUFF manages these sources using the vertical momentum flux factor (FMFAC). For a vertical stack, 1 means full momentum, while 0 means horizontal or capped. FMFAC is equivalent to TIDATA(7) which allows you to define how the FMFAC changes over time for varying emissions.

In other models, the recommended approach is similar to Environmental Protection Agency and Joseph A. Tikvart - Proposal for Calculating Plume Rise for Stacks with Horizontal Release or Rain Caps

Calvin Consulting Group Ltd. can help you with air quality

Are you worried about air quality regulations and permits? There's no need to feel alone. Modelling air dispersion can seem complicated, but Calvin Consulting Group Ltd. makes it easy.

We are like pollution detectives determining how is air pollution caused and how to minimize it easily. Our team of experienced scientists at Calvin Consulting has been helping companies keep the air clean for over 30 years by using special tools to track this kind of stuff. As a result, everyone benefits from cleaner air. 

Calvin Consulting: Why should you choose us?

  • Our meteorologists and dispersion modellers are some of the best in Canada. We'll guide you through every step, from understanding complex regulations to getting approvals.
  • AERMOD and CALPUFF are cutting-edge tools we use to accurately assess potential air emissions from your facility. As a result, you'll meet regulatory requirements and minimize environmental impact.
  • You can run your business with confidence knowing you're compliant with environmental regulations when Calvin Consulting is on your side.

Don't let air quality worries hold you back. Let's talk! Contact Calvin Consulting today!

Barry at Calvin Consulting will help you navigate air quality regulations

PS. We know air dispersion modelling can be expensive. The costs of non-compliance, including fines and delays, can be much higher. We've got competitive rates and a proven track record. With Calvin Consulting, you'll be able to navigate air quality regulations with confidence.

Clean air is our Passion...Regulatory Compliance is our Business.

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Why does the air feels thick sometimes?

Or is it just your imagination? I doubt it; the sneaky culprit of air pollution lurks everywhere. We could benefit from exploring how our daily living and the world around us contribute to this threat, though we may not see it right away.

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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