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Measurement Needs for Evaluating Model Calculations of Carbonaceous Aerosol

This workshop discusses measurement needs to evaluate model calculations of carbonaceous aerosol, including questions about the fraction of PM2.5 mass that is carbonaceous, the primary vs. secondary fractions, source contributions, and transport from upwind locations.

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Measurement Needs for Evaluating Model Calculations of Carbonaceous Aerosol

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  1. Prakash V. Bhave, Ph.D. Physical Scientist EMEP Workshop – PM Measurement & Modeling April 22, 2004 Measurement Needs for Evaluating Model Calculations of Carbonaceous Aerosol

  2. Policy-Relevant Questions* • What fraction of PM2.5 mass is carbonaceous? • What fraction of carbonaceous aerosol is primary vs. secondary? • What are the source contributions to primary carbon? • What fraction of secondary organic aerosol is anthropogenic vs. biogenic? • What fraction of carbon in urban areas is transported from upwind locations? • Existing models can answer these questions, but we need measurements to evaluate the answers * NCEA Carbonaceous PM Workshop Series - 2004

  3. Carbonaceous Fraction of PM2.5 • Reconstruction of carbonaceous mass • Organic mass contains C, H, O, and N atoms • Carbon is measured; rest is estimated • OM/OC ratios of 1.2 – 2.5 have been proposed • Ratio increases with age of aerosol [Turpin & Lim, 2001] • Speciated or FTIR measurements can help • Evaluation approach • In model formulation, OM/OC ratios are known • Convert model predictions to OC, and evaluate against carbon measurements

  4. Carbonaceous Fraction of PM2.5 CMAQ Model Results – Average of 2001 Annual Simulation (TC/PM2.5,dry)

  5. Carbonaceous Fraction of PM2.5 OC/EC inter-network inconsistencies (STN vs. IMPROVE) - STN OC data are not blank-corrected - Different thermal-optical protocols STN data averaged from April ’02 – March ’03* Courtesy of Joann Rice, EPA/OAQPS

  6. Primary vs. Secondary CMAQ–2001 Annual Average (Primary Carbon / Total Carbon)

  7. Primary vs. Secondary • OCpri & OCsec cannot be measured directly • Several indirect estimation methods exist • EC tracer method • Estimate (OC/EC)pri from emissions/transport model [S.Yu, et al., 2004] • Make use of the plentiful, ambient OC and EC data

  8. OC & EC data from SEARCH network (IMPROVE TOR method) • OC/EC in source profiles must be consistent with the ambient monitors • Semi-continuous OC/EC data are needed to check model predictions of diurnal OCsec patterns • Most models predict the OCsec peak at nighttime [Pun et al., 2003] Primary vs. Secondary

  9. Primary vs. Secondary OC/EC splits in the inventory inconsistent with ambient sampling protocols

  10. Apportionment of Primary Carbon Diesel exhaust fraction Biomass combustion fraction - CMAQ results using source apportionment capability (Aug. 1, 1999) - Evaluations will provide direct feedback to emission inventory improvement - Validated results can support control strategy development

  11. Apportionment of Primary Carbon Needs for Model Evaluation • Data types • Source-specific organic tracers (e.g., levoglucosan, hopanes, cholesterol, etc.) [Schauer, et al.] • Primary biogenic carbon (e.g., carbohydrates, vegetative detritus) [M.Hernandez; W. Rogge, et al.] • Semi-continuous wood smoke source tracers? • Spatial resolution • Several urban sites (e.g., each Supersite) • Some representative rural sites • Temporal resolution • 24h data at urban sites for ~1 month per season • 2-6h composites at urban sites to check diurnal variation • Monthly composites at rural sites to check seasonality

  12. What fraction of SOA is anthropogenic? Great uncertainty within model parameterizations Nashville: July 16-18,1995 model inter-comparison yields values of 10% - 40% [Pun et al., 2003] Uncertainties too large to justify controls directed specifically at anthropogenic SOA SOA: Biogenic vs. Anthropogenic

  13. SOA: Biogenic vs. Anthropogenic Needs for Model Evaluation • Data types • 14C can help provide a measure of biogenic SOA;need collocated wood smoke & vegetative detritus data • Source-specific SOA tracers [Edney et al.] Reprinted from: Edney & KleindeinstOAQPS Model Eval Workshop, Chapel Hill, Feb.10, 2004

  14. SOA: Biogenic vs. Anthropogenic CMAQ–2001 Annual Average (Anthropogenic fraction of OCsec)

  15. Carbon fraction of PM2.5 OC, EC data are plentiful; some network inconsistencies OM/OC uncertain, but not essential for model evaluation Primary vs. secondary? Consistent definition of OC and EC across ambient networks and source data Semi-continuous OC & EC Primary source apportionment Source-specific tracers Increase spatial & temporal resolution of organic tracer measurements Anthropogenic vs. biogenic SOA Tracers for aromatic and monoterpene oxidation 14C collocated with wood smoke & detritus markers Summary of Measurement Needs

  16. Acknowledgements • Atmospheric Modeling Division (NOAA/EPA) • Emissions Monitoring & Analysis Division – Air Quality Modeling Group (OAQPS) • Computer Sciences Corporation 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.

  17. Urban Network (STN)PM2.5 = 10.5 mg/m3 CMAQ ModelPM2.5 = 11.5 mg/m3 Carbonaceous Fraction of PM2.5 2001 Network Median Values (~7000 observations)Carbon Value is “blank-corrected” by 1 mg/m3

  18. Apportionment of Primary Carbon Gasoline exhaust fraction Coal combustion fraction - CMAQ results using source apportionment capability (Aug. 1, 1999)

  19. Apportionment of Primary Carbon Oil combustion fraction Natural gas combustion fraction - CMAQ results using source apportionment capability (Aug. 1, 1999)

  20. Apportionment of Primary Carbon Food cooking fraction Paved road dust fraction - CMAQ results using source apportionment capability (Aug. 1, 1999)

  21. Apportionment of Primary Carbon Crustal material fraction Miscellaneous source fraction - CMAQ results using source apportionment capability (Aug. 1, 1999)

  22. Missoula Cleveland Bronx SLC Indy Fresno S.L. Baltimore Tulsa Richmond Charlotte Atlanta Birmingham 13 urban STN sites 16 rural IMPROVE sites Local vs. Regional Contribution Differences between urban (STN) and paired rural site (IMPROVE) Reprinted from: N. FrankOAQPS Model Eval Workshop, Chapel Hill, Feb.10, 2004

  23. Local vs. Regional Contribution Differences between urban and paired rural site(s) - Carbonaceous mass dominates the “urban excess” Reprinted from: N. FrankOAQPS Model Eval Workshop, Chapel Hill, Feb.10, 2004

  24. Urban contribution 5.4 mg/m3 Urban contribution 10.1 mg/m3 Local vs. Regional Contribution CMAQ Results at 1km resolution (OC+EC)Along Pennsylvania - New Jersey border

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