1. Cristina Gonzalez-Maddux ITEP
Intro to AERMOD
If using preferred models, don’t need to demonstrate applicability
If you use models other than those preferred, the responsibility is on you to prove to EPA that the model you’ve chosen to use is appropriate. EPA has already evaluated the performance of these models, so you don’t have to. It has evaluated several models and decided to recommend them for use in specific circumstances.
Cristina Gonzalez-Maddux
ITEP, Research Specialist

2. + = AERMIC AERMOD Origins
AMS/EPA Regulatory Model Improvement Committee – formed in 1991; goal of introducing boundary layer met into regulatory dispersion models – introduced planetary boundary layer (PBL) parameterizations
1991 American Meteorological Society and USEPA initiated a formal collaboration AERMIC
AMS/EPA Regulatory Model
= AERMIC

3. What is AERMOD?
Recall: Preferred/Recommended models listed in Appendix W
AERMOD – “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.”
Two data input processors: AERMET – met preprocessor and AERMAP – terrain preprocessor characterizes terrain and generates receptor grids using USGS digital elevation data
Proposed by EPA in April 2003 as a replacement for the ISCST3 model (Industrial Source Complex Short Term Model)
June 2003, EPA released AERMOD: Latest Features and Evaluation Results (EPA-454/R )

4. What is AERMOD?
What do AERMOD results look like? And what does the output file tell me?
What are the inherent assumptions behind AERMOD?

5. AERMOD Adoption
Previous model: ISCST3  In 2000 EPA proposed replacing with AERMOD
Improvements?
Many!
New and improved algorithms: Building downwash (PRIME – uses Pasquill-Gifford stability class in and beyond downwash wake to assess mixing and dispersion); dispersion in both convective and stable boundary layers; plume rise and buoyancy; plume penetration into elevated inversions; treatment of receptors on all types of terrain; treatment of elevated, near-surface and surface level sources; computation of vertical profiles of wind, turbulence, and temperature

6. What does the model output tell us?
Put simply  Location map and an isopleth – An isopleth map generalizes and simplifies data with a continuous distribution(AEGIS, Jackson State University)
Kesarkar et al. 2007, Atmos. Env.

7. When do we use AERMOD? US EPA Preferred Models
AERMOD – recommended for regulatory use for
Point, volume or area sources
Rural or urban areas
Simple or complex terrain
Transport distance up to 50 km (31 miles)
Specifically??  permits: i.e. oil & gas, hard rock mining, coal mining
For distances over 50 km – CALPUFF
Consider: AERMOD distance limitations are theoretically 50 km
Plume would have to travel at 50 km/hr to arrive at the receptor in a one hour run time
50 km

8. What are the limitations of AERMOD?
Steady-state model
“If the model represents the average state of a variable (e.g. wind direction) over a certain period of time, the model is termed steady-state.”
Suitable for circumstances in which “time and space scales are sufficiently large that variability in the emissions, meteorology, or effects can be ignored or averaged.”
Are most of these variables actually stable? That depends.
CALPUFF is a non-steady state, time-and-space dependent Gaussian puff model.

9. Case Studies
Tribal lands – Confederated Tribes of the Umatilla Indian Reservation
Public lands – Rosemont Copper Mine in AZ