Modeling For Managers aq-ppt5-11
Types of Models Near-field *Preferred: EPA AERMOD model 50km CLASS II; Increment Far-field CALPUFF 50km 100+km CLASS I; Chemical Transformation What is used at MPCA
History of Modeling Point Source Modeling Gaussian Plume Model (1930 s) Maximum ground-level impacts/distance Still in use! (AERMOD) Urban/Large Scale Photochemical Urban/Large Scale problems (1970 s) Lagrangian Modeling Puff (Sulfur) CALPUFF Eulerian Modeling V/H grid cells (Ozone) Large-scale air quality models Long-range transport Chemical and physical properties Local, regional, national & global scale (CMAQ, CAMX, UAM) >1980
Air Dispersion Models Exist to Move pollution from a modeled source to a modeled world Images courtesy Lakes Environmental
Source Types
Point Source Characteristics Emission Rate Grams/Second Stack Height Stack Diameter Exit Temperature Exit Velocity
Model World Characteristics Wind blows Sun creates thermals Terrain Interacts Image courtesy Lakes Environmental Building creates eddies Pollutants transform Image courtesy Lakes Environmental NO + O3 => NO2 + O2 Nearby sources Background
Grams/Second Air Quality Model NO + O3 => NO2 + O2
Receptors Definition: the locations where impacts are predicted. uniform, polar grid uniform, Cartesian grid discrete, Cartesian grid
Final Results
Modeled Source Emission Rate How much stuff is being emitted each second Image courtesy Lakes Environmental Concentration is proportional to Emission Rate
Modeled Source Stack Height How high the release point is above ground level Partially determines how much pollution can reach the ground General rule: as stack height increases ( ), concentration decreases (fl)
Modeled Source Stack Diameter How wide the vent is at the release point Partially determines exit velocity General rule: as diameter increases ( ), concentration increases ( )
Modeled Source Exit Velocity How fast the material exits the stack Partially determines plume rise. General rule: as exit velocity increases ( ), concentration decreases (fl)
Modeled Source Exit Temperature How hot the material is as it exits the stack Partially determines plume rise General rule: as exit temperature increases ( ), concentration decreases (fl)
Plume Rise Warm plume rises until it s temperature is the same or cooler than the air above it Plume Rise Partially determines how much pollution reaches the ground
Image courtesy Lakes Environmental Model World Wind
Model World Stability Unstable Stable Image courtesy Lakes Environmental Unstable Image courtesy Lakes Environmental Stable Cool Warm Warm Cool
Model World Stability Sunny Afternoon Partly Cloudy Aftn. Cloudy Anytime Foggy Morning Clear Morning Partly Cloudy Mrng. Images courtesy Lakes Environmental The sun and cloud layers drive how these patterns set up. The model ingests these data from weather balloons.
Model World Terrain Stable Atmosphere Air can go over or around depending on how fast the air is moving
Model World Terrain Unstable Atmosphere All air moves over the hill
Model World Terrain
Image courtesy Lakes Environmental Model World Buildings
Model World Buildings Image courtesy Lakes Environmental Image courtesy Lakes Environmental
Model World Buildings Image courtesy Lakes Environmental If stack is at least 2.5 times building height, downwash will not come into play.
Model World Buildings L = Lesser of the BH or PBW BH = Building Height PBW = Projected Building Width Image courtesy Lakes Environmental If building is 5L away from stack then downwash also not in play.
Model World Chemical Transformation Ozone Limiting Method (OLM) Plume Volume Molar Ratio Method (PVMRM) Same Chemistry for both Methods: NO + O3 => NO2 + O2 Single Stacks Multiple Stacks 2D - Ambient ozone applied at each receptor 3D - Ozone mixed across volume of the plume.
Model World Nearby Sources
Nearby Source Tool
Background Background air quality includes pollutant concentrations due to: (1) Natural sources; (2) nearby sources other than the one(s) currently under consideration; and (3) unidentified sources. 40 CFR Part 51, Appendix W to Part 51 Guideline on Air Quality Models
Background Criteria Pollutant Monitors Ozone (O 3 ) Fine Particles (PM 2.5 ) Carbon Monoxide (CO) Sulfur Dioxide (SO 2 ) (Courtesy: G Pratt, MPCA)
Facility + Nearby Sources + Background
How we use Air Dispersion Modeling Today MPCA/Regulatory Uses: Evaluate compliance with NAAQS and regulatory requirements Determine extent of emission reductions required Evaluate sources in permit applications Risk assessment Industry/Other Uses: Assist in design of effective control strategies Emergency planning by public safety responders/emergency management
Levels of Modeling: Screening How we use Air Dispersion Modeling Today NAAQS PSD SIL Refined Analysis of these Critical Values
How we use Air Dispersion Modeling Today MPCA/Regulatory Uses - Programs Supported Prevention of Significant Deterioration (PSD) Air Quality Permits Non-PSD: Federal Part 70 and Title V and State Only-Permits State Implementation Plan (SIP) Environmental Review (EAW & EIS)
How we use Air Dispersion Modeling Today
Questions Models Try to Answer Will a new source degrade air quality? Will Minnesota stay in attainment of air quality standards? Will human health be protected from hazardous pollutants?
AERMOD Can t Tell Us Exact location of an exceedance Exact time of an exceedance Exact concentration of an exceedance
Key Issues & Challenges New short-term NAAQS Background concentrations Emission inventories Model limitations Timeliness of EPA
Key Issues Current Actions EPA Guidance is scheduled to change Modification of model Clarify definitions MPCA Workgroup Modification of MPCA Modeling Guidance
Future Directions Modeled Background using MnRisks Modeling more involved and complicated Attainment issues Gridded met/terrain data Regional & photochemical modeling will be more common SIP components Environmental Justice and Air Quality (City of Minneapolis)
Disclaimer: Some images used throughout the presentation are courtesy of Lakes Environmental. Use of these images is not an endorsement for the use of Lakes Environmental s products.