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

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

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

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

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

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

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

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

Controlling Processes (2) Plume rise Turbulence

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

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

Controlling Process (5) Deposition

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

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

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

Planetary Boundary Layer Convective Boundary Layer Planetary Boundary Layer Stable Boundary Layer

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

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

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

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.

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

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

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

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

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

Dispersion Model - HYSPLIT Where did it come from?

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