Prakash Bhave, Golam Sarwar, Havala Pye, George Pouliot, Heather Simon, Jeffrey Young, Chris Nolte, Ken Schere, Rohit Mathur

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Impact of ISORROPIA II on air quality model
predictions

• Prakash Bhave, Golam Sarwar, Havala Pye, George
  Pouliot, Heather Simon, Jeffrey Young, Chris
  Nolte, Ken Schere, Rohit Mathur
• U.S. Environmental Protection Agency
• CMAS Conference
• Chapel Hill, NC
• October 24 26, 2011

Acknowledgements S. Napelenok, K. Fahey, S.
Howard, S. Roselle, S. Capps
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Overview

• What is ISORROPIA?
• Motivation for ISORROPIA II
• Implementation in CMAQ v5.0ß
• model results interspersed throughout
• Summary Future Work

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What is ISORROPIA?

• Inorganic, gas/particle, thermodynamic,
  equilibrium module embedded in numerous air
  quality models (e.g., CMAQ, GEOS-Chem, CAMx,
  CHIMERE)
• Computationally efficient
• Consumes lt10 of CMAQ model run time
• Fun facts
• Developed by Thanos Nenes for his Masters thesis!
• ISORROPIA means equilibrium in Greek
• In CMAQ, subroutine is purposely misspelled
  ISOROPIA

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What is ISORROPIA?

• Schematic of PM species in CMAQs AE5 module
• ISORROPIA I treats SO4/NO3/NH4/Na/Cl/H2O system

COARSE MODE
2 FINE MODES
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Why ISORROPIA II?Motivation 1 Numerical
Stability
In previous versions of CMAQ, doubling EC
emissions in Massachusetts could cause a 1.7mg/m3
increase in NO3- over California. This
erroneous result was primarily due to ISORROPIA I
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Why ISORROPIA II?Motivation 2 Coarse NO3 Bias
Reference CMAS poster by Bhave Appel (2009)

• Hypothesis bias is due to CMAQs treatment of
  crustal species (ASOIL, ACORS) as
  thermodynamically inactive.

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Why ISORROPIA II?

• Optimized activity coefficient calculations
• to minimize model runtime and improve numerical
  stability
• Treats thermodynamics of crustal materials
• Mg2, K, Ca2
• MgSO4, Mg(NO3)2, MgCl2, K2SO4, KHSO4, KNO3, KCl,
  CaSO4, Ca(NO3)2, CaCl2
• Peer-reviewed literature Fountoukis Nenes
  (ACP, 2007)
• ISORROPIA versions released in CMAQ

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Implementation in CMAQ v5.0ß
COARSE MODE
2 FINE MODES
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Implementation in CMAQ v5.0ß

• Revised coarse-mode mass transfer (new species
  shown in red)

COARSE MODE
2 FINE MODES
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Implementation in CMAQ v5.0ß

1. Compare ISORROPIA v2.1 versus v1.7
2. Evaluate numerical stability
3. Add new species to CMAQ Mg, K, Ca

Zero emissions of K, Ca, Mg, to compare with
ISORROPIA v1.7
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ISORROPIA v1.7 vs. v2.110-day Summer Test Case
(new old)
µg m-3
ppb
?PM2.5 is driven by a NO3- decrease v2.1
partitions more NH3 HNO3 to gas phase than v1.7
in warm season. ?O3 is very small, a side effect
of ?HNO3.
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ISORROPIA v1.7 vs. v2.110-day Winter Test Case
(new old)
?PM2.5 is larger and more widespread during
winter driven by a NO3- increase opposite of
summer result ?O3 is negligible Remainder
focus on winter test period
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ISORROPIA v1.7 vs. v2.1Test of Numerical
Stability
Doubled EC emission rate in a Massachusetts grid
cell (right), and plotted the domainwide ?NO3-
(below)
v1.7
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Add New Species to CMAQ Mg, K, CaStep 1.
Anthropogenic PM2.5
S Mg, K, Ca
Fine-particulate crustal cations are concentrated
in Midwest and urban areas road dust, ag soil,
construction
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Add New Species to CMAQ Mg, K, CaStep 2.
Speciation of Sea Salt

• Previously, we had to scale up Na emissions from
  sea salt to balance the negative charges of Cl-
  SO42- because CMAQ could not track Mg, K, and Ca.
• In CMAQv5.0 AE6, fine-particulate sea salt is
  entirely speciated into Na, Mg, K, Ca, Cl, and
  SO4.
• To minimize transported spcs in CMAQv5.0, coarse
  sea salt is speciated into Cl, SO4, and a new
  lumped species (ASEACATK) that represents total
  sea-salt cations.
• ASEACAT is disaggregated in CMAQ only when
  individual species are needed (e.g., ISORROPIA,
  CLDPROC, postproc)

Fine-mode Speciation
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Add New Species to CMAQ Mg, K, CaStep 3.
Speciation of Coarse PM Emissions

• In NEI, anthropogenic coarse PM (PMC) is
  dominated by
• Unpaved Road Dust (47.5)
• Agricultural Soil (25.3)
• Paved Road Dust (11.4)
• Construction Dust (9.6)
• Mining Quarrying Dust (6.1)
• PM10-2.5 profiles taken from SPECIATE database,
  for sources above
• Composite speciation profile shown on left

Anthropogenic PMC
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Add New Species to CMAQ Mg, K, CaStep 3.
Speciation of Coarse PM Emissions

• 5 coarse-mode species are tracked explicitly in
  CMAQ.
• Rest are lumped into ACORS disaggregated only
  when needed within CMAQ

Anthropogenic PMC
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Add New Species to CMAQ Mg, K, CaStep 3.
Speciation of Coarse PM Emissions

• Speciation profile (left) is composited from 4
  desert soil PM10-2.5 profiles in SPECIATE
  database.
• Only SO4, NO3, Cl, NH4, H2O are tracked
  explicitly in CMAQ.
• Rest are disaggregated from ASOIL only when
  needed in CMAQ.

Coarse Windblown Dust
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CMAQ Results10-day Winter Test Case (new old)
Coarse NO3 (ANO3K)
Fine NO3 (ANO3IJ)
Left. The increase in ANO3K across the Midwest
and central California is likely due to
partitioning of HNO3 to coarse soil/dust
particles. Right. We see a corresponding
decrease in fine-mode NO3 at the same
locations. Not shown. Other species are
affected to a much smaller degree.
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• Summary
• Compared to v1.7, ISORROPIA v2.1
• is more numerically stable!
• puts slightly more NO3- in the gas phase during
  summer.
• puts slightly more NO3- in particle phase during
  winter.
• ISORROPIA v2.1 is fully implemented in CMAQ v5.0,
  taking advantage of its capabilities to handle
  Mg, K, Ca.
• In CMAQv5.0, coarse-mode NO3 increases inland, at
  the expense of fine NO3.

• Future Work
• Evaluate CMAQv5.0 against impactor measurements
• Refine estimates of coarse PM emissions
• Explore computational burden of v2.1 prelim
  analysis suggests 12 slowdown

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Appendix
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CMAQ details

• CMAQv4.7.1 uses ISORROPIA 1.7
• Implemented ISORROPIA 2.1 in CMAQv4.7.1
• Test period covered for 10 days in 2002
• January - winter
• July - summer
• Continental US domain with 36-KM grid-cells
• Used same IC and BC
• Several tests were conducted (with ISORROPIA 1.7
  ISORROPIA 2.1)
• Normal emissions (without Ca, Mg, and K)
• Sensitivity runs by doubling EC emission in one
  grid-cell in Massachusetts
• Normal emissions Ca, Mg, and K however these
  were not included in ISORROPIA
• Normal emissions Ca, Mg, and K these were
  included in ISORROPIA