1. Introduction to Modeling – Part II
Rodney S. Skeen, Ph.D., P.E.
Confederated Tribes, Umatilla

2. Objective
Provide a general understanding of regulatory air dispersion modeling tools
Where will it go and should I care?

3. Uses for Air Models Facility permitting
EXAMPLE: Site a new source, regulatory requirements and thresholds
Regulatory and policy assessments
EXAMPLE: Decide between options for national auto emissions
Identify potential sources for a daily air quality exceedance
Forecasts pollutant concentrations
EXAMPLE: Air quality index forecasting

4. Air Pollution Models
Mathematically simulate physical and chemical processes to predict pollution movement
Modeling approach varies to fit requirements
Computational speed
Size of model region
Spatial and temporal resolution
Time period of concern
Controlling processes
POINT: One size DOES NOT fit all

5. Model’s View of World Meteorology Topography and Geography
COPC Particles
COPC Vapors
COPC Vapors
Topography and Geography

6. Model’s View of World (cont…)
COPC phases
Vapor
Particle
Particle-bound
Deposition mechanisms
Wet
Dry
Meteorology
Wind Speed, Direction
Temperature profile
Solar energy
Precipitation
Topography/Geography

7. Model’s View of World (cont…)
Calculate concentration map

8. Controlling Processes (1)
Diffusion: Molecular mixing because of concentration differences
Advection: Movement with bulk flow (wind)

9. Controlling Processes (2)
Plume rise
Turbulence

10. Controlling Processes (3)
Dispersion: Total plume spread caused by three dimensional advection (turbulence) and diffusion
This…
…or That

11. Controlling Processes (4)
Chemical Reaction
Flow restrictions
CH4 + OH ---> CH3 + H2O
     CH3 + O2 ---> CH3OO
     CH3OO + NO ---> CH3O + NO2
     CH3O + O2 ---> HCHO + HO2
       hn (l <330 nm)      HCHO ---> HCO + H
     HCO + O2 ---> CO + HOO
      H + O2 ---> HOO

12. Controlling Process (5)
Deposition

13. Many Models Available
Dispersion Models: HYSPLIT, AERMOD, ISCST3, CALPUF
Photochemical Models: CMAQ, CAMx, REMSAD, UAM-V®
Receptor Models: CMB, UNMIX, PMF
Many, many others

14. Model Types
Dispersion Models: Estimate pollutants at ground level receptors
Photochemical Models: Estimate regional air quality, predicts chemical reactions
Receptor Models: Estimate contribution of multiple sources to receptor location based on multiple measurements at receptor

15. Dispersion Models - AERMOD
Steady-state (Gaussian) plume model
Planetary boundary layer turbulence structure and scaling
Multiple sources, source types
Building downwash
Limited to 50 km radius
Replaced ISCST3 as preferential dispersion model

16. Planetary Boundary Layer
Convective
Boundary
Layer
Planetary
Boundary
Layer
Stable
Boundary
Layer

17. Gaussian Plume Model
Plume assumed to spread in a Gaussian manner in both horizontal and vertical dimension
Plume moves in single direction

18. Gaussian Plume Model
Meteorological conditions sets dispersion in y- and z-dimensions
Expressed in standard deviation (σ)

19. AERMOD Applications
Predicting near source impacts of a contaminant plume (< 50 km).
EXAMPLE: Permitting a new source
From Subject Received
StuartHarris FW: Tribal Energy Funding Opportunities 9/29/2006

20. Dispersion Model - CALPUF
Non-steady state model
Time/space varying meteorological conditions
Gaussian “puff” approach to dispersion
Applicable to hundreds of meters
EPA preferred model for simulating long-range transport of pollutants
Primary and secondary pollutants
Many features similar to AERMOD
Similar features include building downwash, multiple sources, multiple source types, complex terain.

21. Gaussian Puff Model
“Puffs” of pollutants are acted upon by hourly meteorological data
Puff W2 W1
S.S. Plume

22. Dispersion Model - CALPUF
Many features similar to AERMOD
Multiple sources and source types
Building downwash
Plume rise
Complex terrain

23. Dispersion Model - CALPUF
Unique Applications
Class I impact studies
Evaluate impacts of forest fire
Reservation wide impact study (multiple sources)
Overwater transport and coastal situations

24. Dispersion Model - HYSPLIT
HYSPLIT a modeling tool used for computing both
Wind trajectories in three dimensions
Complex pollutant dispersion, deposition patterns
Provides short-term forecasts using National Weather Service data

25. Dispersion Model - HYSPLIT
Forward predication (dispersion) in short-term
Do I allow a proscribed burn?

26. Dispersion Model - HYSPLIT
Where did it come from?

27. Summary
Models convert numerical representation of system to concentration map
Scale of problem
Controlling processes
Available data
Many specialty models are available for specific applications – know your need
AERMOD: Long-term, within 50 km
CALPUF: Long-term, >50 km, more complex weather
HYSPLIT: Short-term impacts