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Atmospheric Dispersion Modeling: The Need and How to Use AERMOD for Air Quality Impacts Analysis

Updated: Mar 30, 2023

Air quality is a critical factor in maintaining a healthy and sustainable environment. Businesses, industries, and governments all play a role in ensuring that air quality standards are met, and one key aspect of this is understanding how pollutants disperse in the atmosphere. Atmospheric dispersion modeling is a valuable tool for predicting the spread of pollutants and assessing their impacts on the environment and public health. In this blog post, we will discuss why atmospheric dispersion modeling is often needed and provide an overview of the general steps to use the AERMOD model for air quality impacts analysis.



AERMOD is the Environmental Protection Agency's (EPA's) preferred short-range (<50 kilometers) dispersion modeling system, and is described like this:

"A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain."

Steady-state plume model: A plume model is a mathematical representation of how a plume disperses in the air. In a steady-state model, the concentration of the substance and the atmospheric conditions are assumed to be constant over time, simplifying the analysis.


Air dispersion based on planetary boundary layer (PBL) turbulence structure: The planetary boundary layer is the lowest part of the atmosphere that is directly influenced by the Earth's surface. This layer is characterized by turbulence, which is caused by the interaction of air with the surface and various obstacles (mountains and such). In this model, the turbulence structure within the PBL is used to describe how the pollutants disperse in the air.


Scaling concepts: Scaling is a technique used in modeling to make the problem more manageable by simplifying certain aspects. In this case, scaling concepts are applied to the turbulence structure to create a more manageable model that still captures the essential features of the dispersion process.


Treatment of both surface and elevated sources: This model considers both sources of pollution at ground level (surface sources) and those above ground level (elevated sources), such as emissions from stacks.


Simple and complex terrain: The model takes into account the effects of different types of terrain on the dispersion of the substance. Simple terrain refers to relatively flat areas with few obstructions, while complex terrain includes features such as hills, valleys, or urban environments with many buildings.


Why Atmospheric Dispersion Modeling is Often Needed

  1. Regulatory compliance: Air quality regulations require industries and other sources of emissions to demonstrate compliance with established standards. Atmospheric dispersion models, like AERMOD, help assess the concentration of pollutants at various distances from the source and determine if they meet the required standards. One such set of standards is the National Ambient Air Quality Standards (NAAQS). Atmospheric dispersion modeling is often a mandatory requirement for obtaining permits when emissions exceed specific thresholds defined by the regulatory agency, ensuring that air quality standards are maintained and potential impacts are assessed.

  2. Environmental Assessments (EA) & Environmental Impact Statements (EIS): EIAs or EISs are used to analyze the potential environmental impacts of proposed projects. Atmospheric dispersion modeling is an essential component of these assessments, helping to predict the dispersion of pollutants and identify potential risks to human health and the environment.

  3. Incident response: In cases of accidental releases of hazardous substances, dispersion models can predict the spread and concentration of pollutants, providing valuable information for emergency response teams and decision-makers.

  4. Urban planning: Dispersion models can help urban planners to determine the optimal location for new industrial facilities, taking into account existing pollution sources and the potential impacts on air quality.

  5. Air quality management: By identifying pollution hotspots and understanding the behavior of pollutants in the atmosphere, dispersion models can support the development of effective air quality management strategies and emission reduction measures.

General Steps to Use AERMOD for Air Quality Impacts Analysis


AERMOD (American Meteorological Society/Environmental Protection Agency Regulatory Model) is a widely used atmospheric dispersion model. Here are the general steps for using AERMOD in air quality impacts analysis:

  1. Define the problem: Identify the emission sources, pollutants, and receptors (e.g., residential areas, schools, sensitive ecosystems, or other areas the public may have access to) that need to be analyzed.

  2. Gather input data: Obtain the necessary meteorological, topographical, and land use data for the study area. This includes wind speed and direction, temperature, humidity, and terrain elevation. Depending on the project, this data could be provided by the agency, purchased from a third party, or collected onsite.

  3. Emission data: Collect detailed information on the emission sources, including the location, height, and exit velocity of the emission point, as well as the emission rates and characteristics of the pollutants.

  4. Set up the model: Configure the AERMOD model according to the study requirements, selecting the appropriate options for meteorological data processing, terrain analysis, and receptor grids.

  5. Run the model: Input the gathered data into the model and run the simulations, generating output files containing predicted pollutant concentrations at each receptor location.

  6. Analyze the results: Evaluate the model results by comparing predicted pollutant concentrations to regulatory standards and assessing the potential impacts on human health and the environment.

  7. Validate the model and document the: If possible, compare the model predictions with available monitoring data to verify the accuracy of the results and make adjustments if necessary.

Conclusion


Atmospheric dispersion modeling, specifically using the AERMOD model, is an essential tool for assessing air quality impacts and ensuring compliance with regulations. By understanding how pollutants disperse in the atmosphere and evaluating their potential impacts on human health and the environment, decision-makers can develop effective strategies for managing air quality and minimizing risks.

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