Assessment of SAPRC07 with Updated Isoprene Chemistry against Outdoor Chamber Experiments

1. Assessment of SAPRC07 with Updated Isoprene Chemistry against Outdoor Chamber Experiments Yuzhi Chena, Roger Jerrya, Kenneth Sextona, Jason Surratta, William Vizuetea aUniversity of North Carolina at Chapel Hill 13th Annual CMAS Conference, Chapel Hill, NC 27 Oct 2014 1

2. Introduction

3. Motivation - Updated SAPRC07 in CMAQ Xie et al. (2013) updated SAPRC07 with more explicit isoprene chemistry with additional OH and NO3 oxidation pathways that produce SOA precursors. • Isoprene epoxydiols (IEPOX) • OH/HO2 from Hydrox-peroxy aldehydes (HPALD) • Isoprene nitrates more explicit Updated isoprene oxidation scheme for isoprene + OH [Xie et al., 2013, ACP] Yuzhi Chen 3

4. Chemistry Good Enough?Compensating Error? • CMAQ runs suggest improved model performance • Uncertainties Remain: isoprene nitrates yield from ISOPO2 + NO pathway & NOX recycling efficiency • Objective • Can Xie model ozone? • How radical budgets and nitrogen cycling altered? [Xie et al., 2013, ACP] 4

5. Methodologies • Experimental: • 24 isoprene runs • Compounds measured: O3, NOX, Isoprene,CO, HCHO… UNC dual gas-phase chamber, Pittsboro, NC, 1994 • Modeling: • MORPHO (UNC) • PERMM (Python-based Environment for Reaction Mechanisms/Mathematics) 5

6. Result

7. Model Performance Ozone Peak NO-NO2 crossover time time 7

8. NO/NO2 Crossover Time High NOX Lower NOX 8

9. NO/NO2 Crossover Time High NOX Lower NOX • Xie predicts earlier NO-NO2 crossover for all isoprene runs 9

10. Ozone Peak High NOX Lower NOX • Xie is better • But not significant • Both over-predict • Xie is worse 10

11. Ozone Peak High NOX Lower NOX • Xie predicts higher ozone for all isoprene runs 11

12. Model Performance Summary • For All Runs: • Xie predicts earlier crossover • Xie predicts higher ozone • For Lower NOX experiments • Xie pushes the performance towards the wrong direction However, statistics doesn’t tell us the story! 12

13. Case Study

14. High NOX Lower NOX O3, NOX, isoprene concentration times series 0.97 ppm 0.85 ppm 0.75 ppm 0.57 ppm 0.64 ppm 0.61 ppm 0.53 ppm 0.53 ppm 0.52 ppm ISOP: 0.26 ppm, NOX: 0.45 ppm, (ISOP/NOX: 0.58) ISOP: 1.26 ppm, NOX: 0.35 ppm (ISOP/NOX: 3.73) 14

15. Reaction Rate of VOCs + OH High NOX ISOP: 1.26 ppm, NOX: 0.35 ppm (ISOP/NOX: 3.73) 15

16. Integrated Reaction Rate of VOCs + OH High NOX Lower NOX 16

17. High NOX Lower NOX OH conc. HO2 from Aldehydes 17

18. Lower NOx High NOx Why Xie makes more Ozone? Sources of NO2 • High NOX — 65% NO2 made through NO + O3 for SAPRC07; 47% made through recycling from NOZ for Xie • Lower NOX — 77% more NO2 recycled from NOZ for Xie 18

19. NO2 Recycling Rate Lower NOX • Xie predicts 64% more PANs than SAPRC07 • Which accounts for 85% of the total increase in recycled NO2 Yuzhi Chen 19

20. Summary

21. Conclusion • Xie predicts earlier NO-NO2 crossover time and higher ozone peak than original SAPRC07; • The cause is increased VOC + OH reactions and thus elevated HOX (OH & HO2) production from aldehydes; • Under low NOX condition, Xie goes in the wrong direction (bias 4.92% to 11.08%); • Over-prediction of second ozone peak driven by increased NO2 recycling from organic nitrates, mostly PANs (85%). Future Work • Modeling gas-phase SOA precursors (Methacrolein) • Incorporating the CMAQ SOA module into MORPHO and test the Xie mechanism against aerosol chamber experiments 21

22. Acknowledgment We thank Dr. Ying Xie and Deborah Luecken at EPA for providing the CMAQ source code of the Xie mechanism and CSQY file. We are also grateful to Blaine Heffron for technical assistance in modeling, and our former colleague Dr. Haofei Zhang, who provided insight and expertise that greatly assisted this research. • Special Thanks • Dr. William Vizuete, Dr. Jason Surratt, Dr. Ken Sexton, Dr. Evan Couzo, MAQ/CHAQ group, Dr. Harvey Jeffries, Dr. Harshal Parikh Yuzhi Chen 22

23. References • Xie et al., 2013, Atmos. Chem. Phys., 13(16):8439–8455. Available at: http://www.atmos-chem-phys.net/13/8439/2013/ • Hutzell et al., 2011, Atmos. Environment, 46: 417-429. • Crounse et al., 2011, PCCP, 13:13607-13613. • da Silva et al., 2010, Environ. Sci. & Tech. 44 (1) :250-6. • Henderson et al., 2009, Poster at the 8th CMAS Conference, Chapel Hill, NC. 23

24. Thank you!Questions?

25. Backup Slides

26. Sensitivity Runs Lower NOX case: JN2697RED * K = (4.07e+8*EXP(-7694/TK) cm3/s • Halving ISOPO2 isomerization rate has no impact on O3 • ISOPN yields zero-out reduces O3 peak by 5.5% Yuzhi Chen 26

27. Radical Cycle High NOX Lower NOX OH NO 27

28. Radical Cycle Overview High NOx ————> Lower NOX 28

29. hv Radical Cycles OH cycle = Q/q ＋ H2O Termination Loss of Radicals Propagation Products New Radical hv q Q O3 Production NO —> NO2 hv Oxidation, Photolysis & Reaction Nitrogen products Loss of NO and NO2 e E New NO O3 Reaction Loss (NOZ) Net O3 Production NO cycle = E/e organic processes inorganic processes 29

30. hv Radical Cycles - High NOX Case OH cycle = Q/q ＋ H2O Termination Loss of Radicals Propagation Products New Radical hv q Q O3 Production NO —> NO2 hv Oxidation, Photolysis & Reaction Nitrogen products Loss of NO and NO2 e E New NO O3 Reaction Loss (NOZ) Net O3 Production NO cycle = E/e organic processes inorganic processes 30

31. Generic Atmospheric Ozone Chemistry RONO2 VOC + OH RO2 OH (ISOP + OH) + NO2 + NO HNO3 O2 RO HO2 hv RCHO O3P O2 O3 NO + O3 NO2 hv 31