Application of the CMAQUCD Aerosol Model to a Coastal Urban Site

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• Application of the CMAQ-UCD Aerosol Model to a
  Coastal Urban Site
• Chris Nolte
• NOAA Atmospheric Sciences Modeling Division
• Research Triangle Park, NC
• 6th CMAS Conference
• Chapel Hill, North Carolina
• October 3, 2007

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Coauthors

• Prakash Bhave NOAA/EPA
• Robin Dennis NOAA/EPA
• Jeff Arnold EPA
• Max Zhang Cornell University
• Tony Wexler UC Davis

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Motivation

• Certain ecosystems very sensitive to nitrate
  deposition
• In coastal environments, coarse sea salt
  particles may act as sinks for nitric acid
• NaCl HNO3 ? NaNO3 HCl
• Most regional air quality models either neglect
  sea salt aerosol dynamics entirely or have crude
  estimates of sea salt emissions/boundary
  conditions

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CMAQ-UCD

• Sectional aerosol module coupled to CMAQ 4.4
• 9 size bins, 0.039 20 mm.
• SO4, NO3, NH4, Na, Cl, EC, POA, SOAa, SOAb, dust,
  H, H2O
• Dynamic mass transfer between gas/aerosol phases
  (non-equilibrium)
• Simplified thermodynamics derived from AIM
• SOA treatment similar to CMAQ
• No coagulation, no heterogeneous reaction of N2O5

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Application to BRACE

• Bay Region Atmospheric Chemistry Experiment
  assess sources of nitrogen deposition to Tampa
  Bay
• Extensive measurements in May 2002rich data set
  for this application
• This evaluation is not intended as a comparison
  against the CMAQ modal aerosol model!

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Modeling Configuration

• 32 km continental U.S. domain, windowed to 8 km,
  then 2 km.
• Will present results from 8 km only.
• MM5 30 layers, Pleim-Xiu PBL and land-surface
  schemes, Grell microphysics.
• Used sea surface temperature from GOES satellite.
• US EPA 1999 National Emissions Inventory,
  projected to 2002.
• CMAQ 4.4, SAPRC99, 21 layers
• April 21 June 3, 2002

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Sea Salt Emissions

• Size-dependent fluxes of sea salt Na, Cl-, SO42-
  over open ocean and surf zone from
  parameterizations of Gong et al. and de Leeuw et
  al.
• see K.M. Zhang et al., 2005
• Initial tests with 100 m surf zone width resulted
  in too much sea salt
• Reduced surf zone width to 50 m

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Modeling Domain
8 km domain (158 x 158)
Observational Sites
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Observations

• Compare against two surface data sets
• 10- or 12-stage MOUDI (Evans et al., 2004).
• 23-h samples at 3 sites, 15 sampling days
• Semi-continuous parallel plate wetted denuder
  (Dasgupta et al., 2007)
• Inlet 50 cut point 12.5 mm.
• See Jeff Arnolds poster for comparisons against
  aircraft measurements!

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Two co-located MOUDIs at Sydney 2nd measurement
is shown in red.
Nitrate is consistently underpredicted
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Size distributions May 14
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Size distributions May 14
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Size distributions May 15
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Size distributions May 15
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Chloride Displacement by NitrateNO3 / (NO3 Cl)
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Conclusions

• Modeled size distributions of SO4, NH4, Na, and
  Cl generally in good agreement with obs, but NO3
  too low by a factor of 2.
• Missing source of NO3?
• Too rapid dry deposition?
• Though NO3 is too low, model correctly predicts
  it is predominantly in the coarse size sections.
• Cl and Na concentrations are reasonably unbiased,
  indicating sea salt emissions and transport are
  correct on average.
• Frequent overpredictions in early morning Cl (not
  shown) and underprediction of extent of chloride
  displacement by nitrate.
• Underestimated rate of mass transfer?
• Inaccurate thermodynamics?
• Other processes?

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Acknowledgments

• Met modeling
• Lara Reynolds, Nancy Hwang
• Emissions
• Charles Chang, Lucille Bender, George Pouliot
• Observational data
• Sandy Dasgupta, Ben Hartsell

Disclaimer A portion of the research presented
here was performed under the Memorandum of
Understanding between the U.S. Environmental
Protection Agency (EPA) and the U.S. Department
of Commerce's National Oceanic and Atmospheric
Administration (NOAA) and under agreement number
DW13921548. This work constitutes a contribution
to the NOAA Air Quality Program. Although it has
been reviewed by EPA and NOAA and approved for
publication, it does not necessarily reflect
their policies or views.