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Air Toxics Program

IDEM Air Toxics > Modeling > Site Specific Modeling Information Site Specific Modeling Information

When IDEM and other regulatory agencies perform air toxics modeling they want to get as accurate a picture of the modeled facility as they can. To this end, site-specific modeling parameters are often collected about a facility to aid in the modeling process. Some of the more common site-specific information is illustrated and explained below:

  • Site Location:
    • The geographic coordinates of the site. This is important to be sure that other inputs used are appropriate.
  • Emission Rate:
    • The amount of each pollutant emitted by the source. This is one of the most important pieces of information since this greatly affects the concentrations that will be breathed in at ground level.
  • Stack Height:
    • The height of the smokestack from which the pollutant is released. The higher the stack, the farther the pollutant will travel, and the more it will spread out, before it reaches ground level where people will be exposed to it.
  • Stack Diameter:
    • Looking down on the smokestack, this is the distance from one side of the stack to the opposite side of the smokestack. This plays a roll in calculating how fast the emissions exit the smokestack.
  • Exit Temperature:
    • The temperature of the gas exiting the stack. If the gas exiting the stack is hotter than the air around the smokestack, it is more likely to rise, meaning longer travel before it reaches ground level. If it is cooler than the surrounding air, it is likely to more quickly sink to ground level.
  • Meteorology:
    • While site-specific meteorology is rarely collected to aid in modeling, weather conditions representative of the area are used to calculate ground-level concentrations of pollutants. For example, if IDEM is modeling a source located in Indianapolis the weather information collected at the Indianapolis International Airport is often used in the process.