Plume-in-Grid Modeling for PM & Mercury Prakash Karamchandani, Krish Vijayaraghavan, Shu-Yun Chen &...
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Transcript of Plume-in-Grid Modeling for PM & Mercury Prakash Karamchandani, Krish Vijayaraghavan, Shu-Yun Chen &...
Plume-in-Grid Modeling for PM & Mercury
Prakash Karamchandani, Krish Vijayaraghavan, Shu-Yun Chen & Christian Seigneur
AERSan Ramon, CA
5th Annual CMAS ConferenceOctober 16–18, 2006
Chapel Hill, NC
Why Use Plume-in-Grid Approach?
Plume Size vs Grid Size (from Godowitch, 2004)
• Artificial dilution of stack emissions
• Unrealistic near-stack plume concentrations
• Incorrect representation of plume chemistry
• Incorrect representation of plume transport
Limitations of Purely Grid-Based Approach
Plume Chemistry & Relevance to PM and Mercury Modeling
Early Plume Dispersion
NO/NO2/O3 chemistry1
2Mid-range Plume Dispersion
Reduced VOC/NOx/O3 chemistry — acid formation from OH and NO3/N2O5 chemistry
Long-range Plume Dispersion
3
Full VOC/NOx/O3 chemistry — acid and O3 formation
Possible reduction of HgII to Hg0
Mercury Chemistry in Power Plant Plumes
• Evidence of HgII reduction in power plant plumes (Edgerton et al., ES&T, 2006; Lohman et al., ES&T, 2006)
• Reduction of HgII by SO2 (possibly via heterogeneous reaction
on particles) is compatible with the global Hg cycling budget (Seigneur et al., J. Geophys. Res., in press)
CMAQ-MADRID-APT-Hg
• Based on CMAQ v 4.5.1, March 2006 release
• MADRID: Model of Aerosol Dynamics, Reaction, Ionization and Dissolution
• APT: Advanced Plume Treatment with embedded plume model SCICHEM (state-of-the science treatment of stack plumes at the sub-grid scale)
• Mercury treatment included
• Consistent treatments for chemical transformations (gas- and aqueous-phase) and PM in the host model and the embedded plume model
Model Components
CMAQ v. 4.5.1
MADRID PM Treatment with MercuryCMAQ-MADRID-Hg
SCICHEM-MADRID-HgPM and Hg Treatment based on CMAQ-MADRID-Hg
CMAQ-MADRID-APT-Hg
SCICHEM
• Three-dimensional puff-based model
• Second-order closure approach for plume dispersion
• Puff splitting and merging
• Treatment of plume overlaps
• Optional treatment of building downwash
• Optional treatment of turbulent chemistry
• PM, gas-phase and aqueous-phase chemistry treatments consistent with host model
Atmospheric Mercury
• Mercury is present mostly as three “species” in the atmosphere
– Elemental mercury (Hg0)
– Divalent gaseous mercury:
• HgCl2, Hg(OH)2, HgO, etc.
• referred to collectively as HgII or reactive gaseous mercury (RGM)
– Particulate-bound mercury:
• HgII or Hg0 adsorbed on PM
• mostly divalent
• referred to collectively as Hgp
Application to Southeastern U.S.
• Simulation period: 2002
• Grid resolution: 12 km x 12 km, 19 layers (up to ~15 km)
• Meteorology and emissions inventory from Georgia EPD and VISTAS
• Non-Hg ICs/BCs from Georgia EPD – 5 day model spinup for each quarter
• Two annual simulations with CMAQ-MADRID-APT-Hg
– With SO2 + HgII reduction reaction
– Without this reaction
Boundary Conditions for Mercury Species
• Boundary conditions (BCs) for mercury were obtained from a 2001 simulation conducted over the United States with the Trace Element Analysis Model (TEAM)
• Spatially and temporally (hourly) varying BCs of Hg0, HgII, and Hgp
Preliminary Results from Plume Event Evaluations
• Several power plant plume events observed at SEARCH monitoring locations (Edgerton et al., ES&T, 2006)
• To compare the modeled plume events with observations, the plume information in the embedded plume model is used to calculate subgrid-scale concentrations downwind of the power plant impacting a SEARCH monitoring location
• Plume concentrations are sampled at an array of receptors along an arc; the center of the arc is the power plant of interest and the arc extends to 30o on each side of the monitoring location
• The receptor location with the closest match of modeled SO2 peak increment to the observed peak increment is used for comparison purposes
Monitoring Stations in SEARCH networkhttp://www.atmospheric-research.com/studies/SEARCH/index.html
operated by Atmospheric Research & Analysis, Inc. (ARA)
Comparison of Measured and Simulated Peak SO2 Increments
DateMonitoring
LocationMeasured Peak (ppb)
Simulated Peak (ppb)
MADRID MADRID-APT
July 5 YRK 49 19 42
July 18 PNS 12 11 21
July 19 PNS 9 4 4
July 20 BHM 11 16 11
July 21 YRK 67 12 21
July 21 BHM 13 1 < 1
July 27 CTR 34 3 13
July 30 BHM 19 11 19
July 31 BHM 10 15 13
July 31 YRK 8 5 8
Comparison of Measured and Simulated Peak SO2 Increments
DateMonitoring
LocationMeasured Peak (ppb)
Simulated Peak (ppb)
MADRID MADRID-APT
Jan 3 YRK 18 8 10
Jan 4 YRK 9 4 4
Jan 7 YRK 7 3 7
Jan 9 YRK 11 8 13
Jan 10 YRK 16 5 4
Jan 11 CTR 11 5 11
Jan 15 YRK 8 7 7
Plume Event on July 5, 2002Hg Plume Increments
ModelHg0 (pg m-3) HgII (pg m-3) HgII/(Hg0 + HgII)
Obs. Model Obs. Model Obs. Model
MADRID-APT-Hg with HgII reduction reaction 411 190 46 9 0.1 0.05
MADRID-APT-Hg without HgII reduction reaction
411 60 46 119 0.1 0.67
MADRID-Hg with HgII reduction reaction
411 20 46 23 0.1 0.54
MADRID-Hg without HgII reduction reaction
411 20 46 27 0.1 0.58
Source: Plant Bowen; Monitoring Location: Yorkville
Plume Event on July 21, 2002Hg Plume Increments
ModelHg0 (pg m-3) HgII (pg m-3) HgII/(Hg0 + HgII)
Obs. Model Obs. Model Obs. Model
MADRID-APT-Hg with HgII reduction reaction 188 70 79 42 0.29 0.37
MADRID-APT-Hg without HgII reduction reaction
188 60 79 96 0.29 0.62
Source: Plant Bowen; Monitoring Location: Yorkville
Power-Plant Contributions to 24 hr Average Sulfate Concentrations on July 5
CMAQ-MADRID-Hg CMAQ-MADRID-APT-Hg
Conclusions
• Observed plume events are better captured in the plume-in-grid approach than in the purely gridded approach
• Preliminary evaluation results suggest that observed RGM to TGM ratios during plume events are well simulated only when a plume-in-grid approach is used and a pathway for reducing HgII to Hg0 by SO2 is included
• A purely gridded approach typically overestimates power plant contributions to PM2.5 because SO2 to sulfate and NOx to nitrate conversion rates are overestimated (Karamchandani et al., Atmos. Environ., in press)
• A purely gridded approach will also overestimate power plant contributions to RGM concentrations and depositions if a mechanism exists to reduce HgII to Hg0 in power plant plumes
Ongoing Work
• Complete simulations for entire calendar year
• Complete model performance evaluation:
– SEARCH: Continuous gas, PM mass and components, Hg
– Other air quality networks: AQS, IMPROVE, CASTNET
– Wet deposition: NADP, MDN
• Control scenario simulations