AERMOD: DESCRIPTION OF MODEL FORMULATION1On assignment to the Atmospheric Research and Exposure Assessment Laboratory, U.S. Environmental Protection Agency.2 EPA-454/R-03-004 September 2004AERMOD: DESCRIPTION OF MODEL FORMULATION By:Alan J. Cimorelli, U. S. Environmental Protection Agency, Region 3Steven G. Perry1, Atmospheric Sciences Modeling Division/Air ResourcesLaboratory/NOAA, MD-80, USEPAAkula Venkatram, College of Engineering, University of California at RiversideJeffrey C. Weil, Cooperative Institute for Research in Environmental Sciences,University of ColoradoRobert J. Paine, ENSR CorporationRobert B. Wilson, U. S. Environmental Protection Agency, Region 10Russell F. Lee, Charlotte, NC 28269Warren D. Peters, U.S. Environmental Protection Agency, OAQPSRoger W. Brode, MACTEC Federal Programs, Inc. Durham, NC, 27709James O. Paumier MACTEC Federal Programs, Inc. Durham, NC, 27709U.S. Environmental Protection AgencyOffice of Air Quality Planning and StandardsEmissions Monitoring and Analysis DivisionResearch Triangle Park, North Carolina3DisclaimerThis report has been reviewed by the Office of Air Qualtiy Planning and Standards, U.S.Environmental Protection Agency, and has been approved for publication. Mention of tradenames or commercial products does not constitute endorsement or recommendation for use.4AcknowledgmentsThis project was made possible through the continued support of Mr. Joe Tikvart, of EPA’sOffice of Air Quality Planning and Standards (OAQPS), and Mr. Frank Schiermeier, of NOAA’sAtmospheric Sciences Modeling Division. The authors are particularly grateful to Dr. GaryBriggs, and Mr. John Irwin, of NOAA’s Atmospheric Sciences Modeling Division, for theirthorough and constructive review of an earlier version of this document. Finally, we would liketo thank the many scientists who participated in peer reviews and beta testing.5Table of Contents1 Introduction ..............................................................81.1 Background .........................................................81.2 The AERMIC Focus: A Replacement for the ISC3 Model ......................91.3 Model Development Process ...........................................101.4 Purpose of Document .................................................112 Model Overview ..........................................................123 Meteorological Preprocessor (AERMET) .....................................153.1 Energy Balance in the PBL ...............................................153.1.1 NET RADIATION .............................................163.1.2 TRANSITION BETWEEN THE CBL AND SBL ....................163.2 Derived Parameters in the CBL ............................................173.2.1 FRICTION VELOCITY (u*) & MONIN OBUKHOV LENGTH (L) IN THE CBL...............................................................173.2.2 CONVECTIVE VELOCITY SCALE (w*) .............................183.3 Derived Parameters in the SBL ............................................193.3.1 FRICTION VELOCITY (u*) IN THE SBL ............................193.3.2 SENSIBLE HEAT FLUX (H) IN THE SBL............................213.3.3 MONIN OBUKHOV LENGTH (L) IN THE SBL .......................213.4 Mixing Height ......................................................213.4.1 CONVECTIVE MIXING HEIGHT (zic) ...............................223.4.2 MECHANICAL MIXING HEIGHT (zim) ..............................224 Vertical Structure of the PBL - AERMOD’s Meteorological Interface .............244.1 General Profiling Equations ...........................................244.1.1 WIND SPEED PROFILING ........................................244.1.2 WIND DIRECTION PROFILES .....................................274.1.3 PROFILES OF THE POTENTIAL TEMPERATURE GRADIENT .........274.1.4 POTENTIAL TEMPERATURE PROFILING ..........................294.1.5 VERTICAL TURBULENCE CALCULATED ..........................304.1.6 LATERAL TURBULENCE CALCULATED BY THE INTERFACE .......334.2 Vertical Inhomogeneity in the Boundary Layer as Treated by the INTERFACE ...365 The AMS/EPA Regulatory Model AERMOD ..................................405.1 General Structure of AERMOD Including Terrain ..........................415.2 Concentration Predictions in the CBL ....................................455.2.1 DIRECT SOURCE CONTRIBUTION TO CONCENTRATIONCALCULATIONS IN THE CBL ....................................5265.2.2 INDIRECT SOURCE CONTRIBUTION TO CONCENTRATIONCALCULATIONS IN THE CBL ....................................535.2.3 PENETRATED SOURCE CONTRIBUTION TO CONCENTRATIONCALCULATIONS IN THE CBL ....................................545.3 Concentrations in the SBL .............................................545.4 Treatment of Lateral Plume Meander ....................................555.5 Estimation of Dispersion Coefficients ....................................575.5.1 DISPERSION FROM AMBIENT TURBULENCE ......................585.5.2 BUOYANCY INDUCED DISPERSION (BID) COMPONENT OF Fy AND Fz...............................................................625.5.3 TREATMENT OF BUILDING DOWNWASH .........................625.6 Plume Rise Calculations in AERMOD ...................................635.6.1 PLUME RISE IN THE CBL ........................................635.6.2 PLUME RISE IN THE SBL ........................................645.7 Source Characterization ..............................................665.8 Adjustments for the Urban Boundary Layer ...............................666 List of Symbols ...........................................................707 APPENDIX: Input / Output Needs and Data Usage ............................757.1 AERMET Input Data Needs ............................................757.1.1 METEOROLOGY ................................................757.1.2 DIRECTIONALLY AND/OR MONTHLY VARYING SURFACECHARACTERISTICS ............................................757.1.3 OTHER ........................................................757.1.4 OPTIONAL .....................................................767.2 Selection and Use of Measured Winds, Temperature and Turbulence in AERMET..................................................................767.2.1 THRESHOLD WIND SPEED .......................................767.2.2 REFERENCE TEMPERATURE AND HEIGHT .......................767.2.3 REFERENCE WIND SPEED AND HEIGHT