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Impact of ISORROPIA II on air quality model predictions






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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.
Impact of ISORROPIA II on air quality model predictions

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Slide 1

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

Slide 2

Overview

What is ISORROPIA?

Motivation for ISORROPIA II

Implementation in CMAQ v5.0β

model results interspersed throughout

Summary & Future Work

1

Slide 3

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

Slide 4

NO3-

NH4+

SO42-

Cl-

Na+ equivalents

Soil & PMCanth

H2O

HNO3

EC

What is ISORROPIA?

  • Schematic of PM species in CMAQ’s AE5 module

  • ISORROPIA I treats SO4/NO3/NH4/Na/Cl/H2O system

NO3-

NH4+

SO4=

Na+ equiv’s

Cl-

H2O

NH3

POC

SOA

H2SO4

Other

HCl

SVOCs

H2O

2 FINE MODES

COARSE MODE

Slide 5

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

ΔNO3-

Slide 6

Why ISORROPIA II?Motivation #2: Coarse NO3 Bias

Reference: CMAS poster by Bhave & Appel (2009)

  • Hypothesis: bias is due to CMAQ’s treatment of crustal species (ASOIL, ACORS) as thermodynamically inactive.

Slide 7

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

Slide 8

NO3-

NH4+

SO42-

Cl-

Na+ equivalents

Soil & PMCanth

H2O

HNO3

EC

Implementation in CMAQ v5.0β

NO3-

NH4+

SO4=

Na+

Cl-

H2O

NH3

POC

SOA

H2SO4

Other

HCl

SVOCs

H2O

2 FINE MODES

COARSE MODE

Slide 9

NO3-

NH4+

SO42-

Cl-

SEACAT includes Na+,Mg2+,K+,Ca2+

Soil & PMCanth

also include Na+,Mg2+,K+,Ca2+

H2O

HNO3

EC

Implementation in CMAQ v5.0β

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

NO3-

NH4+

SO4=

Na+, Mg2+, K+, Ca2+

Cl-

H2O

NH3

POC

NCOM

SOA

H2SO4

Fe, Al, Si, Ti, Mn, Other

HCl

SVOCs

H2O

2 FINE MODES

COARSE MODE

Slide 10

Implementation in CMAQ v5.0β

Compare ISORROPIA v2.1 versus v1.7

Evaluate numerical stability

Add new species to CMAQ: Mg, K, Ca

Zero emissions of K, Ca, & Mg, to compare with ISORROPIA v1.7

9

Slide 11

ISORROPIA v1.7 vs. v2.110-day Summer Test Case (new – old)

ΔPM2.5

ΔO3

µg m-3

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.

Slide 12

ISORROPIA v1.7 vs. v2.110-day Winter Test Case (new – old)

ΔPM2.5 is larger and more widespread during winter

driven by a NO3-increase

• opposite of summer result

ΔO3 is negligible

Remainder: focus on winter test period

ΔPM2.5

µg m-3

Slide 13

ISORROPIA v1.7 vs. v2.1Test 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

Slide 14

Add New Species to CMAQ: Mg, K, CaStep 1. Anthropogenic PM2.5

Σ Mg, K, Ca

Fine-particulate crustal cations are concentrated in Midwest and urban areas: road dust, ag soil, construction

Slide 15

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

Slide 16

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

Slide 17

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

Slide 18

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

Slide 19

CMAQ Results10-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.

Slide 20

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

Slide 21

Appendix

Slide 22

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


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