Intro to Modeling – Terms & concepts
Marti Blad, Ph.D., P.E.
ITEP 5.29.13
AP models vary in complexity
• Mathematically simulate environmental
processes to predict pollution movement and
concentrations
– More than one way to describe w #’s
• Physical, Chemical and Biological World
• Solar radiation is energy or process driver
– The Sun
The Sun’s impact on Earth’s surface
AP Physical Scale
• Determine Limitations & Assumptions
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Scale = size of area modeled
Resolution = level of detail
Other Physical processes; meteorology, source types
Topography; urban vs rural, water bodies, mountains
Detail for Inputs and outputs of model
Model
Domain Scale
Resolution
Microscale
200m x 200mx 100 m
5m
Mesoscale (urban)
100Km x 100Km x 5Km
2 Km
Regional
1000Km x 1000Km x 10Km
20 Km
Synoptic (continental)
3000Km x 3000Km x 20Km
80 Km
Global
65000Km x65000Km x20Km
AP Model Time periods
• Long term or short term temporal period
• Affects resolution (spatial detail)
– Data input and data output
– Minutes vs hours vs days
• Physical processes match time scales
– Atmospheric temperature profiles
• Chemical reactions affected by solar intensity
– Changes every second!
• Emission source rates continuous or changing
– Equilibrium or steady state
Large Scale
• Advection: Movement with bulk flow (wind)
Small Scale
• Diffusion: Molecular mixing because of
concentration differences.
• High concentration moves to lower
concentration
Where large and small meet
• Dispersion: Total plume spread caused by three
dimensional advection (turbulence) and diffusion
This…
…or That
Dispersion affected by stack height, building locations, and topography
Surface conditions
Topography
Terrain
Planetary boundary layer and surface roughness
Convection
• Plume rise = buoyancy
Ambient vs exit temperature affect air movement
Turbulence & eddies
Moving objects move air molecules - cause currents
Physics & chemistry meet
• Reflection, absorption and deposition
Which Chemicals?
• Source type
• Chemical Reactions
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
Mechanisms: Oxidation and reduction, thermal, photochemical, hydrolysis
Understand model limits & assumptions
Many Models Available
• Dispersion Models: HYSPLIT, AERMOD,
ISCST3, CALPUF
• Photochemical Models: CMAQ, CAMx,
REMSAD, UAM-V®
• Receptor Models: CMB, UNMIX, PMF
• Many, many others
Terms & Concept review
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Advection
Diffusion
Domain (area vs computer)
Conservative
Reactive
Kinetic
Discrete (vs continuous)
Receptor
• Albedo
• Anthropogenic
• Deposition
– Wet vs Dry
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Lumped parameters
Algorithm
Laminar
Photochemical
What is purpose in modeling?
Physical, Chemical, and Biological processes can be modeled
Model’s View of World
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Chemical Processes
Reactive or conservative
Chemical of Concern
Biological impact
Mathematical Processes
– Eulerian, Lagrangian,
– Gaussian
– Time scale
• Physical Processes
• Meteorology
– Wind Speed, Direction
– Solar energy = reactions
– Precipitation
• Topography/Geography
• Deposition mechanisms
• Source Type
Summary
• Models convert numerical representation of system to
concentration map or picture
– Scale of problem; time and space
– Controlling processes; meteorology, topography, and source
– Available data; quality and quantity