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
U.S. EPA Office of Research & Development
October 25, 2011
Overview
1. What is ISORROPIA?
2. Motivation for ISORROPIA II
3. Implementation in CMAQ v5.0β
• model results interspersed throughout
4. Summary & Future Work
1
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
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 <10% 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
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
What is ISORROPIA?
• Schematic of PM species in
CMAQ’s AE5 module
• ISORROPIA I treats
SO4/NO3/NH4/Na/Cl/H2O system
HNO3
EC
POC
NO3NH4+
=
SOA
SO4
Na+ equiv’s
Cl-
SVOCs
Other
NO3NH4+
SO42ClNa+ equivalents
NH3
H2SO4
Soil & PMCanth
HCl
H 2O
H 2O
H 2O
2 FINE MODES
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
COARSE MODE
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
ΔEC
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
ΔNO3-
Why ISORROPIA II?
Motivation #2: Coarse NO3 Bias
Grand Canyon National Park: May 1 – 31, 2003 (n = 15)
Great Smoky Mountains NP: July 22 – Aug. 19, 2004 (n = 14)
NH4+
Na+
NO3-
Cl-
Mass concentration dM/dlnD p (μg/m3)
Mass concentration dM/dlnD p (μg/m3)
SO4=
SO4=
Aerodynamic diameter (μm)
NH4+
Na+
NO3-
Cl-
Aerodynamic diameter (μm)
Reference: CMAS poster by Bhave & Appel (2009)
• Hypothesis: bias is due to CMAQ’s treatment of crustal
species (ASOIL, ACORS) as thermodynamically inactive.
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
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
CMAQ
v4.5 v4.6 v5.0
ISORROPIA v1.5 v1.7 v2.1
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
Implementation in CMAQ v5.0β
HNO3
EC
POC
SOA
NO3NH4+
SO4
Na+
=
ClSVOCs
Other
NO3NH4+
SO42ClNa+ equivalents
NH3
H2SO4
Soil & PMCanth
HCl
H 2O
H 2O
H 2O
2 FINE MODES
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
COARSE MODE
Implementation in CMAQ v5.0β
• Revised coarse-mode mass
transfer (new species shown in
red)
HNO3
EC
POC
NCOM
SOA
SVOCs
NO3NH4+
=
SO4
Na+, Mg2+,
K+, Ca2+
Fe, Al, Si,
ClTi, Mn,
Other
H 2O
NH3
NO3NH4+
SO42ClSEACAT includes
Na+,Mg2+,K+,Ca2+
H2SO4
Soil & PMCanth
also include
Na+,Mg2+,K+,Ca2+
HCl
H 2O
H 2O
2 FINE MODES
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
COARSE MODE
Implementation in CMAQ v5.0β
1. Compare ISORROPIA v2.1
versus v1.7
2. Evaluate numerical stability
Zero emissions
of K, Ca, & Mg,
to compare with
ISORROPIA v1.7
3. Add new species to CMAQ: Mg, K, Ca
9
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
ISORROPIA v1.7 vs. v2.1
10-day Summer Test Case (new – old)
ΔPM2.5
µg m-3
ΔO3
ppb
ΔPM2.5 is driven by a NO3- decrease
• v2.1 partitions more NH3 & HNO3 to gas phase than v1.7 in warm season.
ΔO3 is very small, a side effect of ΔHNO3.
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
ISORROPIA v1.7 vs. v2.1
10-day Winter Test Case (new – old)
ΔPM2.5
ΔPM2.5 is larger
and more
widespread
during winter
driven by a NO3increase
• opposite of
summer result
ΔO3 is negligible
Remainder:
focus on winter
test period
µg m-3
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
ISORROPIA v1.7 vs. v2.1
Test of Numerical Stability
ΔEC
Doubled EC emission rate in a Massachusetts grid cell (right),
and plotted the domainwide ΔNO3- (below)
v1.7
v2.1
* Numerical stability of ISORROPIA v2.1 is greatly enhanced relative to v1.7
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
Add New Species to CMAQ: Mg, K, Ca
Step 1. Anthropogenic PM2.5
Σ Mg, K, Ca
Fine-particulate crustal cations are
concentrated in Midwest and urban areas:
road dust, ag soil, construction
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
Add New Species to CMAQ: Mg, K, Ca
Step 2. Speciation of Sea Salt
SO4
7.7%
Other
0.6%
Na
30.7%
• Previously, we had to scale up Na+
emissions from sea salt to balance
the negative charges of Cl- & SO42because 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.
Mg
3.6%
Cl
55.0%
Fine-mode Speciation
Ca
1.2%
K
1.1%
• 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)
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
Add New Species to CMAQ: Mg, K, Ca
Step 3. Speciation of Coarse PM Emissions
NO3
Cl
NH4
H2O
SO4
Na
Mg
Al
Si
Other
K
Ca
EC
NCOM
OC
Ti
Mn
Fe
Anthropogenic PMC
• 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
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
Add New Species to CMAQ: Mg, K, Ca
Step 3. Speciation of Coarse PM Emissions
NO3
Cl
• 5 coarse-mode
species are tracked
explicitly in CMAQ.
NH4
H2O
SO4
Na
Mg
Al
Si
Other
K
Ca
EC
NCOM
OC
Ti
Mn
Fe
Anthropogenic PMC
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
• Rest are lumped into
ACORS &
disaggregated only
when needed within
CMAQ
Add New Species to CMAQ: Mg, K, Ca
Step 3. Speciation of Coarse PM Emissions
• Speciation profile (left) is composited
from 4 desert soil PM10-2.5 profiles in
SPECIATE database.
Cl NH4
H2O
NO3
SO4
Na
Mg
Al
• Only SO4, NO3, Cl, NH4, & H2O are
tracked explicitly in CMAQ.
• Rest are disaggregated from ASOIL
only when needed in CMAQ.
Si
Other
K
Ca
OC
EC
Ti
Mn
Fe
NCOM
Coarse Windblown Dust
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
CMAQ Results
10-day Winter Test Case (new – old)
Coarse NO3 (ANO3K)
Fine NO3 (ANO3I+J)
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.
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
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
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
19
Appendix
20
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division
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
U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division