Postprocessing Model Output for Comparison to Ambient Data

1. Prakash V. Bhave, Ph.D. Physical Scientist PM Model Performance Workshop February 10, 2004 Postprocessing Model Output for Comparison to Ambient Data

2. 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

3. 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

4. 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

5. 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

6. Ambient Equilibration

7. PM2.5 Inlet Simulation PM2.5 = 16.7 mg/m3

8. PM2.5 Inlet Simulation PM2.5 = 15.5 mg/m3

9. PM2.5 Inlet Simulation

10. PM2.5 Inlet Simulation PM2.5 = 14.9 mg/m3

11. 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)

12. 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.

13. Photo- chemistry Cloud Processing Chemical Reactions Horizontal Transport Vertical Mixing Condensation & Evaporation Gas-Phase Emissions Aerosol Emissions Deposition Atmospheric Processes Modeling