Overview 2/10/2015. Anthony J. Sadar, CCM Allegheny County Health Department Air Quality Program. MARAMA Webinar. Part 2: Go to Slide 56.

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1 MARAMA Webinar Anthony J. Sadar, CCM Allegheny County Health Department Air Quality Program Part 2: Go to Slide 56. February 11 & 12, Overview THE ATMOSPHERE Constituents Structure ATMOSPHERIC DYNAMICS Temporal/spatial scale of events AIR POLLUTION DISPERSION Sources Dispersion Receptors AIR DISPERSION MODELING Observation Theory Models Receptors = Sources / Dispersion C = Q S / U Empirical research Statistical approach: = q / ( u y z ) 2 1

2 Overview (Continued) US EPA GUIDELINES Guideline on Air Quality Models (Revised), Appdx. W Other guidance/clarification AERMOD & AERSCREEN Input requirements Output examples Interpretation of results Comparison between AERMOD and AERSCREEN ADDITIONAL MODELS & APPLICATIONS Requirements for regulatory modeling 3 The Atmosphere Constituents Structure 4 2

3 Constituents Permanent Percent Nitrogen (N2) 78.1 Oxygen (O2) 20.9 Argon (Ar) 0.9 Neon (Ne) Variable Water Vapor (H2O) 0 4 Carbon Dioxide (CO2) 0.04 Helium (He) Methane (CH4) Krypton (Kr) Structure Temperature changes with increasing altitude in atmosphere. ]- ABL Not to Scale. 6 3

4 Atmospheric Boundary Layer (ABL) Bottom layer of troposphere starting at earth s surface and extending to several km during sunny afternoons. Structure and height of ABL varies diurnally, during fair weather over land: From tens of meters on mornings with a strong surface temperature inversion (when temperature increases with altitude) to several kilometers during sunny afternoons. 7 Atmospheric Dynamics Temporal/Spatial Scales of Events Source: A World of Weather: Fundamentals of Meteorology, 4 th Edition, by Lee Grenci, Jon Nese, and David Babb, 2008, Figure

5 Conditions of Note Topography Heat Island Effect (Urban/Rural) Land/Water (Diurnal Sea Breeze / Land Breeze ) Mountain/Valley (Diurnal Effects and Channeling) Elevation 9 Conditions of Note (Continued) Overview Source: D. Carruthers, Chpt. 10, Atmospheric Dispersion and Air Pollution Meteorology, in Handbook of Atmospheric Science: Principles and Applications, C.N. Hewitt and A.V. Jackson, Editors,

6 Conditions of Note (Continued) Topography Source: D. Carruthers, Chpt. 10, Atmospheric Dispersion and Air Pollution Meteorology, in Handbook of Atmospheric Science: Principles and Applications, C.N. Hewitt and A.V. Jackson, Editors, Poll Question #1 The Heat Island Effect occurs in the Atmospheric Boundary Layer (True/False) 12 6

7 Poll Question #2 Turbulence is a meso scale temporal event. (True/False) 13 Air Pollution Dispersion Transport and Diffusion of Air Pollution Sources Dispersion Receptors 14 7

8 Air Dispersion Modeling What is Modeling? Modeling Components: Source considerations Dispersion considerations Receptor considerations 15 What Is Modeling? Ascientific model is a tentative representation of an observation based on interpretation of available information; a tool used to simulate real world conditions. Air dispersion modeling, as described by the EPA, uses mathematical formulations to characterize atmospheric processes that disperse a pollutant emitted by a source. Based on emissions and meteorological inputs, a dispersion model can be used to predict concentrations at selected downwind receptor locations. Note that verification of the truth of any model is an impossible task (ASTM International, D , 2010). Models contain assumptions and limitations. 16 8

9 What Is Modeling? (Continued) Observation Theory Models Adapted from: Numerical Weather and Climate Prediction, T. T. Warner, 2011, Fig. 1.1, p Modeling Components Sources Dispersion Receptors 18 9

10 Whence Highest Concentrations? Large Emission Rate Low Plume Rise Overlapping Plumes Stack Tip Downwash Building Induced Downwash Building Cavity 19 Whence Highest Conc.? (Continued) Proximity to Source(s) Terrain Induced Downwash and Channeling High Terrain Short Ground Cover Stable/Stagnant Atmosphere Steady Wind Direction from Source(s) to Receptor(s) 20 10

11 Source Considerations Worst case conditions for emissions: Maximum particle/gas discharge Lowest release height Lowest in vent/in stack temperature Lowest exit gas velocity Shortest distance to property line 21 Dispersion Considerations Worst case meteorology: No precipitation Light winds from source to critical receptor(s) Strong ground based temperature inversion (elevated inversion can also cause problems) Note: Wind Direction is direction from which wind is blowing

12 Receptor Considerations Worst case conditions for receptors: Closest, highest off site location Plume centerline concentrations Elevated receptor for malodor investigations 23 Simple Relationship Sources Dispersion Receptors Receptors = Sources / Dispersion or R = S / D 24 12

13 Simple Dispersion Formula C = Q x S U Where, C is pollutant concentration (g/m 3 ) Q is rate of emissions exiting source (g/s) S is stability of atmosphere (m 2 ) U is horizontal wind speed (m/s) 25 How Does Emission Rate Affect C? 26 13

14 How Does Wind Speed Affect C? 27 Poll Question #3 All else being equal, a pollutant concentration at a receptor will be higher with a higher stack.(true/false) 28 14

15 Poll Question #4 All else being equal, a pollutant concentration at a receptor will be lower at low wind speed.(true/false) 29 How Does Stability Affect C? 30 15

16 Stability Conditions Traditionally, stability of lower atmosphere has been delineated as: 31 How Does Stability Affect Plumes? Smokestack emissions that continuously exhaust to the ambient air are referred to as plumes. Plumes exhibit particular patterns depending upon atmospheric stability

17 Plume Types 33 Simple Dispersion Formula C = Q x S U Where, C is pollutant concentration (g/m 3 ) Q is rate of emissions exiting source (g/s) S is stability of atmosphere (m 2 ) U is horizontal wind speed (m/s) 34 17

18 Empirical Research Field observations suggested that smokestack emissions disperse in a normal way; that is, pollutants spread away from a centerline with a typical bell shaped or Gaussian frequency distribution. 35 Plume Observations Source: Hanna, et al.,

19 Statistical Approach Bell-shaped Curve, Normal, or Gaussian Distribution Source: 37 Statistical Approach (Continued) Probability Density Function: = 1.exp[(-0.5 (x- ) 2 )/2 2 ] (2 ) 1/2 Compare with the fundamental Gaussian plume equation: = q.exp[-0.5 (H 2 / z2 )] y z u 38 19

20 Gaussian Plume Model Source: 39 Gaussian Distribution The bell shaped curves represent a distribution of contaminants across the horizontal (cross wind) and vertical axis. Source: Fundamental Gaussian Plume Equation: = q. exp [-0.5 (H 2 / z2 )] ( u y z ) 40 20

21 Gaussian Distribution (Continued) Fundamental Gaussian Plume Equation: = q. exp [-0.5 (H 2 / z2 )] ( u y z ) Where, = ambient air concentration, q = emission rate,, u = wind speed, y z = dispersion parameters, and H= effective plume height. 41 Gaussian Plume Cross Section Source: Hanna, et al.,

22 Poll Question #5 If a plume concentration is distributed normally pollutant concentration will be highest along the centerline.(true/false) 43 Dispersion Parameters ( y and z ) Source: Turner,

23 Good Engineering Practice Stack Height (H GEP ) H GEP is the greater of: 65 meters For stacks built before 1/12/1979: H GEP = 2.5 H, where H is height of nearby structure(s) For all other stacks: H GEP = H + 1.5L, where L is lesser of H or projected width of nearby structure(s). 45 Flow Around Buildings 46 23

24 Flow Around Buildings (Continued) Source: Saskatchewan Air Quality Modeling Guideline, March Plume Rise Plume rise is also important to pollution dispersal. Plume rise is primarily a function of exit gas temperature and momentum. Generally, Higher temperature = higher plume rise. Higher momentum = higher plume rise. Higher plumes = lower ground level pollutant concentrations

25 Poll Question #6 Buildings can cause plume downwash.(true/false) 49 Types of Mathematical Air Quality Models Lagrangian models simulate dispersion or reactions in parcels of air that move along with the wind trajectory. Eulerian approaches divide the problem domain into fixed grid cells. Various methods are then used to solve equations over the full domain. Slide adapted from: Julie McDill, MARAMA 25

26 Which Models Use Which Math? Lagrangian models Dispersion models (e.g., AERMOD) Trajectory models (e.g., HYSPLIT) Eulerian Photochemical grid models (e.g., CAMx) Slide adapted from: Julie McDill, MARAMA Summary THE ATMOSPHERE Constituents Structure ATMOSPHERIC DYNAMICS Temporal/spatial scale of events AIR POLLUTION DISPERSION Sources Dispersion Receptors AIR DISPERSION MODELING Observation Theory Models Receptors = Sources/ Dispersion C = QS/U Empirical research Statistical approach: =q/( u y z ) 52 26

27 References 53 Links to Resources Meteorology and Atomic Energy 1968: orology/meteorology%20and%20atomic%20energy.pdf Workbook of Atmospheric Dispersion Estimates, 1970: mates_1971.pdf Handbook on Atmospheric Diffusion, 1982: Handbook of Atmospheric Science: Principles and Applications, 2003: EPA s Support Center for Regulatory Atmospheric Modeling (SCRAM) Website: Guideline on Air Quality Models (Revised) (40 CFR 51):

28 55 MARAMA Webinar Anthony J. Sadar, CCM Allegheny County Health Department Air Quality Program December 4,

29 Review THE ATMOSPHERE Constituents Structure ATMOSPHERIC DYNAMICS Temporal/spatial scale of events AIR POLLUTION DISPERSION Sources Dispersion Receptors AIR DISPERSION MODELING Observation Theory Models Receptors = Sources/ Dispersion C = QS/U Empirical research Statistical approach: =q/( u y z ) Overview of Topics for Today US EPA GUIDELINES Guideline on Air Quality Models (Revised), Appdx. W Preferred and Recommended Dispersion Models Examples of Other Models (CAMx and WRF) AERMOD & AERSCREEN Input requirements Output examples Comparison between AERMOD and AERSCREEN AERSCREEN Operation MODELING GUIDANCE AND SUPPORT 29

30 U.S. EPA Guidelines Guideline on Air Quality Models (Revised) Appendix W 40 CFR 51, Nov. 9, 2005 AERMOD Established as Preferred Dispersion Model Out to 50 km EPA s Support Center for Regulatory Atmospheric Modeling (SCRAM) Website EPA Approved Models AERMOD AMS/EPA Regulatory Model CAMx Comprehensive Air quality Model with extensions CMAQ Community Multiscale Air Quality model CALPUFF Originally sponsored by CA Air Resources Board 30

31 Types of Mathematical Air Quality Models Lagrangian models simulate dispersion or reactions in parcels of air that move along with the wind trajectory. Eulerian approaches divide the problem domain into fixed grid cells. Various methods are then used to solve equations over the full domain. Slide adapted from: Julie McDill, MARAMA Which Models Use Which Math? Lagrangian models Dispersion models (e.g., AERMOD) Trajectory models (e.g., HYSPLIT) Eulerian Photochemical grid models (e.g., CAMx) Slide adapted from: Julie McDill, MARAMA 31

32 CAMx Dispersion Model Uses nested three dimensional grids Accounts for average species concentration changes over time within each grid cell volume via: Horizontal advection Vertical transport Sub grid scale turbulent diffusion Dry deposition and wet scavenging Chemical/photochemical reactions Secondary aerosol formation/partitioning CAMx Nested Grids Example of Horizontal Grid Nesting (Fig. 2-2, pg. 2-5) 32

33 CAMx Horizontal Grid Nesting km 0 04 km km ACHD Proposed CAMx Domain 36 km 148 x 112 (-2736, -2088) to (2592, 1944) 12 km 174 x 117 ( 72, -540) to (2160, 864) 04 km 54 x 60 ( 1296, 48) to (1512, 288) 0.8 km 75 x 60 ( 1392, 144) to (1452, 192) Source: ENVIRON Weather Research and Forecasting (WRF) Model State of the science mesoscale numerical weather prediction system developed by NCAR, NOAA, et al. Used worldwide for both operational forecasting and atmospheric research Community model that undergoes continuous evaluation and frequent updates Operates like CAMx, using 3 D grid cells 33

34 AERMOD vs. CAMx AERMOD CAMx Gaussian, straight line dispersion Concentrations within 3 D box Generally non reactive plume Chemical/photochemical reactions Impact distance limited to 50 km Practically unlimited distance Models impact from individual sources to specific receptor points Simple construction, direct and quick operation Generally does not model direct impact of point sources to nearby receptors Complex construction and more sophisticated, time consuming operation Poll Question #7 CAMx is used for permit modeling of stationary industrial sources.(true/false) 68 34

35 What is Dispersion Modeling? Lagrangian Model Purpose: Estimate effect of local sources near field receptors local atmosphere pollutants not affected by chemical transformation Example: AERMOD Slide adapted from: Julie McDill, MARAMA Source: U.S.EPA 35

36 AERMOD Modeling System/Inputs Source: U.S.EPA AERMOD System Inputs/Outputs Source: U.S.EPA 36

37 AERMODModelingSystemAlgorithms Dispersion in Convective and Stable ABLs Plume Rise and Buoyancy PlumeIncursionIntoElevatedInversionsandRe entrainment ComputationofVerticalProfilesofTemp.,Wind,andTurbulence Site specific meteorology beneficial AERMODSystemAlgorithms (Continued) Urban Nighttime Boundary Layer Receptor Considerations On All Types of Terrain Building Wake Effects Improvement in Characterizing Basic ABL Parameters Treatment of Plume Meander 37

38 Poll Question #8 AERMOD is used for permit modeling of stationary industrial sources.(true/false) 75 Poll Question #9 Site specific meteorology is preferred if available.(true/false) 76 38

39 AERMOD Run Example How Is AERMOD Used In Regulatory Work, Such As SIP Preparation? Allegheny County Nonattainment Area 39

40 AERMOD Example Output N Modeling Results for 2011 (Contours every 100 g/m 3 ) Slide adapted from: ACHD s AWMA Presentation, 2014 Q Q Plot of Results Source: ACHD s AWMA Presentation,

41 Source: U.S.EPA AERMOD & AERSCREEN Comparison between AERMOD and AERSCREEN 41

42 AERMOD vs. AERSCREEN Input Bla nkr rr Output examples AERMOD 42

43 Output examples AERSCREEN AERSCREEN Operation What is AERSCREEN? Model Run Demonstration 86 43

44 What Is AERSCREEN? Screening model based on AERMOD Estimates "worst case" 1 hour concentrations from a single source Does not need hourly meteorological data (MAKEMET) Includes conversion factors to estimate "worst case" 3 hour, 8 hour, 24 hour, and annual concentrations (Note: These conversion factors are conservative!) Estimated concentration = or > than AERMOD Degree of conservatism depends on application What s So Good About AERSCREEN? EPA approved (replaced SCREEN3) Provides more realistic, yet conservative values more sophisticated treatment of building wake effects handles winds at 0.5 m/s, et al. incorporates terrain impacts Familiar operation Quick and easy to run But, plug & chug can be GI/GO 44

45 AERSCREEN vs. SCREEN3 Building Wake Effects Modeled With BPIPPRM Incorporates More Detailed Meteorology Albedo, Bowen Ratio, Surface Roughness More Realistic/Site Specific Terrain Impacts Modeled Poll Question #10 AERSCREEN is more conservative than AERMOD (T/F) 45

46 AERMOD & AERSCREEN Comparison AERMOD simulates numerous sources simultaneously while AERSCREEN is limited to a single source Both models: Vertical or horizontal stack, capped stack, rectangular or circular area, flare stack, volume release Building downwash option AERSCREEN results typically more conservative than AERMOD results Operation Of AERSCREEN Interactive command prompt application that runs via interfaces with: site specific matrix of meteorology, terrain and building input, and AERMOD Release conditions: Vertical uncapped or capped stack, horizontal stack, rectangular or circular area, flare, or volume source Models NO x to NO 2 conversion Default values When in doubt follow the instructions The Usual Suspects (typical pitfalls) Does the answer make sense? 46

47 Default Values Model Mode = Rural (+ try Urban) Min/Max Temperatures = K / K Stack Temperature = 0, for ambient temperature Minimum Wind Speed = 0.5 m/s Anemometer Height = 10.0 m Surface Characteristics = 2, AERMET seasonal tables Dominant Surface Profile = 6, grassland (+ try others) Dominant Climate Type = 1, Average Moisture Others The Usual Suspects Mistyping Misconstruing instructions Mixed or incorrect units Mis assigning file names or extensions Misunderstanding wind direction Others Don t Forget to Ask Yourself: Does the answer make sense? 47

48 Modeling Issues Malodors Air toxics Guideline on Air Quality Models, 40 CFR Part 51, Appendix W Others Modeling Demo Before using AERSCREEN, users must have the latest AERMOD executable (09292 or later) AERMAP terrain preprocessor BPIPPRIME executables. These can be downloaded from the AERMOD Modeling System section. [Source: SCRAM Website.] 48

49 Nominal Industrial Source Example Input File (AERSCREEN 11126) Note that the most recent version of the model is AERSCREEN

50 AERSCREEN Modeling Results (Without and With Building) Building Downwash Figure 11. Stack and building orientation for a building oriented 90 degrees to north and stack oriented 45 degrees to north. (Source: AERSCREEN User s Guide, U.S.EPA, 3/2011, p. 20) 50

51 Plane View of Building and Stack Orientation for Example AERSCREEN Run (Source: AERSCREEN User s Guide, U.S. EPA, 3/2011, Figure 35, pg. 56) AERMET Guidance: Albedo 51

52 AERMET Guidance: Bowen Ratio AERMET Guidance: RoughnessLength 52

53 AERSCREEN Results Better ingredients 53

54 Modeling Guidance and Support Guideline on Air Quality Models (Revised) Appendix W 40 CFR 51, Nov. 9, 2005 EPA s Support Center for Regulatory Atmospheric Modeling (SCRAM) Website Model formulation documents, user guides; addendums Model Change Bulletins Clarification memos (Ex., September 30, 2014 memo) pdf Model Clearinghouse State and Local Modeling Guidance Summary THE ATMOSPHERE Constituents Structure ATMOSPHERIC DYNAMICS Temporal/spatial scale of events AIR POLLUTION DISPERSION Sources Dispersion Receptors AIR DISPERSION MODELING Observation Theory Models Receptors = Sources/ Dispersion C = QS/U Empirical research Statistical approach: =q/( u y z ) 54

55 Summary (Continued) US EPA GUIDELINES Guideline on Air Quality Models (Revised), Appdx. W Other guidance/clarification AERMOD & AERSCREEN Input requirements Output examples Interpretation of results Comparison between AERMOD and AERSCREEN ADDITIONAL MODELS & APPLICATIONS Requirements for regulatory modeling References 55

56 Links to Resources Meteorology and Atomic Energy 1968: orology/meteorology%20and%20atomic%20energy.pdf Workbook of Atmospheric Dispersion Estimates, 1970: mates_1971.pdf Handbook on Atmospheric Diffusion, 1982: Handbook of Atmospheric Science: Principles and Applications, 2003: EPA s Support Center for Regulatory Atmospheric Modeling (SCRAM) Website: Guideline on Air Quality Models (Revised) (40 CFR 51):