Visualizing Hazard Index using AERMOD Plot Files and GIS

AERMOD is commonly used for regulatory purposes, such as in the assessment of air quality impacts for new or modified sources in support of the permitting process. Within AERMOD, a .PLT file (plot file) output contains the calculated pollutants concentration at various receptor locations for the designated percentile concentration and selected averaging periods. The .PLT file can be input into visualization software, such as Lakes Environmental's AERMOD View or Trinity Consultants' BREEZE AERMOD, to produce contour plots, charts, or tables that depict the pollutant concentration distribution over the study area.

In a recent project, we encountered a situation where the Hazard Index exceeds 1 in area near the source. However, the current modeling tools can only showcase concentration isopleths for each individual pollutant but not an aggregate. As such, we use the output from the PLT file and leverage the power of ESRI's ArcGIS tool to help us visualize the location of the Hazard Index exceeding 1 and propose mitigation measures for our clients. This article focuses on the visualization of the Hazard Index that is not currently available in AERMOD View or 3D Analyst.

1. Establish point sources and grid receptors and fence line receptors for your facilities. Ensure each source group reflects one pollutant so that you can run multiple pollutants in one AERMOD file.

2. Create a plt file for each Hazard Air Pollutant point source

3. Aggregate the plt for each pollutant using excel's pivot tables, use the X's and Y's and conc column

4. Calculate Hazard Index on excel based on the ratio of each pollutant in relation to the Threshold

5. Import points with Hazard Index with XY extracted from the PLT file and input the Hazard Index to GIS

6. Generate a TIN file in ArcGIS using the prepared Grid, which can be utilized to define the impact area. The highlight areas represents a Hazard Index exceeding 0.8 (red) and 1 (blue).

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