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U.S. EPA Office of Research & Development October 25, 2011 Prakash Bhave, Golam Sarwar, Havala Pye, George Pouliot, Heather Simon, Jeffrey Young, Chris.

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Presentation on theme: "U.S. EPA Office of Research & Development October 25, 2011 Prakash Bhave, Golam Sarwar, Havala Pye, George Pouliot, Heather Simon, Jeffrey Young, Chris."— Presentation transcript:

1 U.S. EPA Office of Research & Development October 25, 2011 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 Acknowledgements: S. Napelenok, K. Fahey, S. Howard, S. Roselle, S. Capps

2 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 1 Overview 1.What is ISORROPIA? 2.Motivation for ISORROPIA II 3.Implementation in CMAQ v5.0β model results interspersed throughout 4.Summary & Future Work

3 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

4 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 SO 4 /NO 3 /NH 4 /Na/Cl/H 2 O system NO 3 - NH 4 + SO 4 = Na + equiv’s Cl - H 2 O POC SOA EC Other HNO 3 NH 3 H2OH2O SVOCs NO 3 - NH 4 + SO 4 2- Cl - Na + equivalents Soil & PMC anth H 2 O COARSE MODE2 FINE MODES H 2 SO 4 HCl

5 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Why ISORROPIA II? Motivation #1: Numerical Stability In previous versions of CMAQ, doubling EC emissions in Massachusetts could cause a 1.7  g/m 3 increase in NO 3 - over California. This erroneous result was primarily due to ISORROPIA I ΔECΔNO 3 -

6 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Hypothesis: bias is due to CMAQ’s treatment of crustal species (ASOIL, ACORS) as thermodynamically inactive. Reference: CMAS poster by Bhave & Appel (2009) Why ISORROPIA II? Motivation #2: Coarse NO 3 Bias

7 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 –Mg 2+, K +, Ca 2+ –MgSO 4, Mg(NO 3 ) 2, MgCl 2, K 2 SO 4, KHSO 4, KNO 3, KCl, CaSO 4, Ca(NO 3 ) 2, CaCl 2 Peer-reviewed literature: Fountoukis & Nenes (ACP, 2007) ISORROPIA versions released in CMAQ

8 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Implementation in CMAQ v5.0β NO 3 - NH 4 + SO 4 = Na + Cl - H 2 O POC SOA EC Other HNO 3 NH 3 H2OH2O SVOCs NO 3 - NH 4 + SO 4 2- Cl - Na + equivalents Soil & PMC anth H 2 O COARSE MODE2 FINE MODES H 2 SO 4 HCl

9 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Implementation in CMAQ v5.0β Revised coarse-mode mass transfer (new species shown in red) NO 3 - NH 4 + SO 4 = Na +, Mg 2+, K +, Ca 2+ Cl - H 2 O POC NCOM SOA EC Fe, Al, Si, Ti, Mn, Other HNO 3 NH 3 H2OH2O SVOCs NO 3 - NH 4 + SO 4 2- Cl - SEACAT includes Na +,Mg 2+,K +,Ca 2+ Soil & PMC anth also include Na +,Mg 2+,K +,Ca 2+ H 2 O COARSE MODE2 FINE MODES H 2 SO 4 HCl

10 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 9 Implementation in CMAQ v5.0β 1. Compare ISORROPIA v2.1 versus v Evaluate numerical stability 3. Add new species to CMAQ: Mg, K, Ca Zero emissions of K, Ca, & Mg, to compare with ISORROPIA v1.7

11 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division ISORROPIA v1.7 vs. v day Summer Test Case (new – old) ΔPM 2.5 µg m -3 ppb ΔO3ΔO3 ΔPM 2.5 is driven by a NO 3 - decrease v2.1 partitions more NH 3 & HNO 3 to gas phase than v1.7 in warm season. ΔO 3 is very small, a side effect of ΔHNO 3.

12 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division ISORROPIA v1.7 vs. v day Winter Test Case (new – old) ΔPM 2.5 µg m -3 ΔPM 2.5 is larger and more widespread during winter driven by a NO 3 - increase opposite of summer result ΔO 3 is negligible Remainder: focus on winter test period

13 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division ISORROPIA v1.7 vs. v2.1 Test of Numerical Stability ΔEC v1.7 Doubled EC emission rate in a Massachusetts grid cell (right), and plotted the domainwide ΔNO 3 - (below) v2.1 * Numerical stability of ISORROPIA v2.1 is greatly enhanced relative to v1.7

14 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Add New Species to CMAQ: Mg, K, Ca Step 1. Anthropogenic PM 2.5 Σ Mg, K, Ca Fine-particulate crustal cations are concentrated in Midwest and urban areas: road dust, ag soil, construction

15 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division Fine-mode Speciation Previously, we had to scale up Na + emissions from sea salt to balance the negative charges of Cl - & SO 4 2- 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 SO 4. To minimize #transported spcs in CMAQv5.0, coarse sea salt is speciated into Cl, SO 4, 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) Add New Species to CMAQ: Mg, K, Ca Step 2. Speciation of Sea Salt

16 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 Anthropogenic PM C In NEI, anthropogenic coarse PM (PM C ) 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%) PM profiles taken from SPECIATE database, for sources above Composite speciation profile shown on left

17 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 Anthropogenic PM C 5 coarse-mode species are tracked explicitly in CMAQ. Rest are lumped into ACORS & disaggregated only when needed within CMAQ

18 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 Coarse Windblown Dust Speciation profile (left) is composited from 4 desert soil PM 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.

19 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division CMAQ Results 10-day Winter Test Case (new – old) Left. The increase in ANO3K across the Midwest and central California is likely due to partitioning of HNO 3 to coarse soil/dust particles. Right. We see a corresponding decrease in fine-mode NO 3 at the same locations. Not shown. Other species are affected to a much smaller degree. Coarse NO 3 (ANO3K)Fine NO 3 (ANO3I+J)

20 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 NO 3 - in the gas phase during summer. –puts slightly more NO 3 - 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 NO 3 increases inland, at the expense of fine NO 3. 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 19

21 U.S. EPA Office of Research & Development, Atmospheric Modeling & Analysis Division 20 Appendix

22 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


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