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

– 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 ResolutionMicroscale 200m x 200mx 100 m 5 m

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

TerrainTopography

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

• Advection• Diffusion• Domain (area vs computer)• Conservative• Reactive• Kinetic• Discrete (vs continuous)• Receptor

• Albedo• Anthropogenic• Deposition

– Wet vs Dry

• Lumped parameters• Algorithm• Laminar• Photochemical

What is purpose in modeling?

Physical, Chemical, and Biological processes can be modeled

Model’s View of World• 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