ASTM_D_6589_-_05_2015.pdf

Designation:D658905(Reapproved 2015)Standard Guide forStatistical Evaluation of Atmospheric Dispersion ModelPerformance1This standard is issued under the fixed designation D6589;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide provides techniques that are useful for thecomparison of modeled air concentrations with observed fielddata.Such comparisons provide a means for assessing amodels performance,for example,bias and precision oruncertainty,relative to other candidate models.Methodologiesfor such comparisons are yet evolving;hence,modificationswill occur in the statistical tests and procedures and dataanalysis as work progresses in this area.Until the interestedparties agree upon standard testing protocols,differences inapproach will occur.This guide describes a framework,orphilosophical context,within which one determines whether amodels performance is significantly different from othercandidate models.It is suggested that the first step should be todetermine which models estimates are closest on average tothe observations,and the second step would then test whetherthe differences seen in the performance of the other models aresignificantly different from the model chosen in the first step.An example procedure is provided in Appendix X1 to illustratean existing approach for a particular evaluation goal.Thisexample is not intended to inhibit alternative approaches ortechniques that will produce equivalent or superior results.Asdiscussed in Section 6,statistical evaluation of model perfor-mance is viewed as part of a larger process that collectively isreferred to as model evaluation.1.2 This guide has been designed with flexibility to allowexpansion to address various characterizations of atmosphericdispersion,which might involve dose or concentrationfluctuations,to allow development of application-specificevaluation schemes,and to allow use of various statisticalcomparison metrics.No assumptions are made regarding themanner in which the models characterize the dispersion.1.3 The focus of this guide is on end results,that is,theaccuracy of model predictions and the discernment of whetherdifferences seen between models are significant,rather thanoperational details such as the ease of model implementation orthe time required for model calculations to be performed.1.4 This guide offers an organized collection of informationor a series of options and does not recommend a specific courseof action.This guide cannot replace education or experienceand should be used in conjunction with professional judgment.Not all aspects of this guide may be applicable in all circum-stances.This guide is not intended to represent or replace thestandard of care by which the adequacy of a given professionalservice must be judged,nor should it be applied withoutconsideration of a projects many unique aspects.The word“Standard”in the title of this guide means only that thedocument has been approved through the ASTM consensusprocess.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisguide.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheres3.Terminology3.1 DefinitionsFor definitions of terms used in this guide,refer to Terminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 atmospheric dispersion model,nan idealization ofatmospheric physics and processes to calculate the magnitudeand location of pollutant concentrations based on fate,transport,and dispersion in the atmosphere.This may take the1This guide is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved April 1,2015.Published April 2015.Originallyapproved in 2000.Last previous edition approved in 2010 as D6589 05(2010)1.DOI:10.1520/D6589-05R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 form of an equation,algorithm,or series of equations/algorithms used to calculate average or time-varying concen-tration.The model may involve numerical methods for solu-tion.3.2.2 dispersion,absolute,nthe characterization of t