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Prakash V. Bhave, Ph.D. Physical Scientist PM Model Performance Workshop February 10, 2004 Postprocessing Model Output for Comparison to Ambient Data
Air Quality Model Photo- chemistry Input Cloud Processing Chemical Reactions Model Output Horizontal Transport Meteorology Model Vertical Mixing Gridded Values of: Aerosol ConcentrationParticle Size DistributionChemical Composition Condensation & Evaporation Emissions Model Air Quality Model AmbientSampling Laboratory Analysis Input Gas-Phase Emissions Aerosol Emissions Deposition AmbientSampling LaboratoryAnalysis Observations Point Values of: PM2.5 Mass ConcPM2.5 Chemical Comp. Traditional PM Model Evaluations Model Evaluation
Model Tuning Model Postprocessing Modification of model outputs to simulate ambient sampling conditions, sampling artifacts, and analytical biases. Notes: • Inputs are unchanged • Atmospheric processing is unchanged • No need to rerun the air quality model Modification of model inputs or atmospheric chemical & physical formulae to improve agreement between model results and observations. e.g., multiply NH3 emissions by 2 and rerun the model e.g., raise or lower the minimum eddy diffusivity and rerun the model e.g., modify a rate constant and/or reaction probability and rerun the model
Postprocessing Air Quality Model Photo- chemistry Input - Adjust for site T,RH - Inlet Collection - Substrate Artifacts - Lab Analyses Cloud Processing Chemical Reactions Horizontal Transport Meteorology Model Vertical Mixing Condensation & Evaporation Output for Eval. Emissions Model PM2.5 Mass ConcPM2.5 Chemical Comp. Gas-Phase Emissions Aerosol Emissions Deposition Model Evaluation AmbientSampling LaboratoryAnalysis Observations Point Values of: PM2.5 Mass ConcPM2.5 Chemical Comp. Enhancing PM Model Evaluations
H2O NO3 Nonvolatile Material SVOC Ambient Equilibration • Models predict both gas and particle-phase concentrations • Gas/particle partitioning of semi-volatile species is a function of T, RH • What if the met model provides a gridded temperature field that is warmer than at the site?i.e., Tmodel > Tambient
PM2.5 Inlet Simulation PM2.5 = 16.7 mg/m3
PM2.5 Inlet Simulation PM2.5 = 15.5 mg/m3
PM2.5 Inlet Simulation PM2.5 = 14.9 mg/m3
Other Postprocessing Steps • Substrate Artifacts • Adsorption/desorption from substrate during sampling • Have been characterized experimentally • Can be estimated with moderate difficulty • Chemical Analyses • Lab conditions = 20-23 ºC, 30-40% RH • Exceeds CRH of NH4HSO4, NH4NO3, NaHSO4, • Aerosol water content can be estimated • Organic Mass/Carbon Ratio • Measurements reported as Organic Carbon • Models assume some ratio (e.g., POA = 1.2 in NEI, SOAb = 1.475 in CMAQ, SOAa = 1.67 in CMAQ)
Acknowledgements Pete Finkelstein, ORD John Irwin, OAQPS Brian Timin, OAQPS Rob Gilliam, ORD Brian Eder, ORD Ken Schere, ORD S.T. Rao, ORD Disclaimer Notice: • This work has been funded wholly by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for presentation.
Photo- chemistry Cloud Processing Chemical Reactions Horizontal Transport Vertical Mixing Condensation & Evaporation Gas-Phase Emissions Aerosol Emissions Deposition Atmospheric Processes Modeling