1. Understanding the impact of isoprene nitrates and OH reformation on regional air quality using recent advances in isoprene photooxidation chemistry Ying Xie 1, Fabien Paulot 2, Robert W. Pinder 1, William P.L. Carter 3, Christopher G. Nolte 1, Deborah J. Luecken 1, William T. Hutzell 1, Paul O. Wennberg 2, and Ron Cohen 4 1 US EPA Office of Research & Development; 2 California Institute of Technology; 3 University of California Riverside; 4 University of California Berkeley 9 th Annual CMAS Conference Chapel Hill, NC

2. 2 Outline Introduction –High NO x chemistry and isoprene nitrates –Low NO x chemistry and HO x recycling Methodology Results –Smog chamber evaluation –INTEX-NA 2004 Conclusions Current and future research

3. 3 Introduction Isoprene is the predominant VOC –Global emissions ~500Tg/yr, oxidized within hours by OH –High NO x : NO –Low NO x : HO 2 /RO 2 High NO x : -> RO + NO 2 formaldehyde, methyl vinyl ketone, methacrolein RO 2 + NO -> RNO 3 ISOP + OH -> RO 2 O3O3 yield (4 -15%)? terminal sinks or recycle NO x ?

4. 4 Introduction Isoprene is the predominant VOC –Global emissions ~500Tg/yr, oxidized within hours by OH –High NO x : NO –Low NO x : HO 2 /RO 2 High NO x : -> RO + NO 2 formaldehyde, methyl vinyl ketone, methacrolein RO 2 + NO -> RNO 3 ISOP + OH -> RO 2 γ*secondary isoprene nitrates + (1- γ)*NO 2 O3O3 yield (4 -15%)? terminal sinks or recycle NO x ?

5. 5 Isoprene nitrates (INs) have large impact on O 3 production – Increase INs yield by a factor 3 decrease global O 3 production by 10% (Wu et al. 2007) Represent a major uncertainty in determining the response of O 3 to future changes in biogenic emissions – Wu et al. (2008a) found lack of sensitivity of O 3 to climate change in southeastern US (12% INs, no NO x recycling) – Racherla and Adams (2006) reported a large O 3 sensitivity for the same area (no INs) Introduction Isoprene is the predominant VOC –Global emissions ~500Tg/yr, oxidized within hours by OH –High NO x : NO –Low NO x : HO 2 /RO 2 High NO x : -> RO + NO 2 formaldehyde, methyl vinyl ketone, methacrolein RO 2 + NO -> RNO 3 ISOP + OH -> RO 2 γ*secondary isoprene nitrates + (1- γ)*NO 2 O3O3

6. 6 Introduction Low NO x: –Gap between modeled and measured OH levels ISOP + OH -> RO 2 RO 2 + HO 2 -> ROOH (Ren et al. 2008) deposition INTEX Modeled

7. 7 Introduction Low NO x: –Gap between modeled and measured OH levels ISOP + OH -> RO 2 RO 2 + HO 2 -> ROOH (Ren et al. 2008) INTEX Modeled deposition x x

8. 8 Objective Incorporate the recent advancements in isoprene photooxidation chemistry into the SAPRC07 photochemical mechanism within the CMAQ model –isoprene nitrates –HO x recycling Evaluate the new scheme with chamber experiment data Compare CMAQ predictions to observations from the summer 2004 INTEX-NA campaign

9. 9 Methodology 2004 INTEX-NA campaign –NASA DC8 (regional scale), NOAA WP-3D (local plumes) –The most spatially extensive observations of alkyl and multifunctional nitrates (∑AN), 12-20% of NO y CMAQ domain and simulation period –36 km US, 148 x 112 horizontal grid cells –July 1 - Aug 15, 2004 Chemical mechanism – BASE: SAPRC07 – ISOP: SAPRC07 + new isoprene scheme CMAQ simulation based on sensitivity studies results

10. 10 Comparisons of the mechanisms

11. 11 Smog chamber evaluation 34 experiments (UCR, UNC, CSIRO) covering ranges of VOC/NO x concentrations –11 with initial NO x below 200 ppb Results: –Higher and improved methyl vinyl ketone –Better O 3 under NO x -limited conditions Bias reduced from -14% to -5%

12. 12 CMAQ model evaluation – isoprene, formaldehyde, NO x NO x (ISOP – BASE) Layer 1, averaged over INTEX-NA isoprene formaldehyde NO x (isop > 300 ppt)

13. 13 Model evaluation – alkyl nitrates all dataisop > 300 ppt

14. 14 Model evaluation – O 3 all dataisop > 300 ppt ISOP – BASE Layer 1, averaged over INTEX-NA 90 th percentile 2-3 ppb increase

15. 15 Biogenic SOA (AISO + ATRP + ASQT+ AOLGB + AORGC) ISOPBASE (ISOP – BASE)/BASE

16. 16 OH all dataisop > 300 ppt isoprene vs OH (Ren et al. 2008) INTEX Modeled

17. 17 OH isoprene vs OH (Ren et al. 2008) INTEX Modeled

18. 18 Conclusions Smog chamber study –Better methyl vinyl ketone –Better O 3 CMAQ simulation –Better Science improvement in alkyl nitrates and almost all species –Slightly higher NO x and O 3 concentrations due to more efficient NO x recycling –Improved O 3 more confidence in predicting the response of O 3 to changes in biogenic emissions Improved OH, but levels are still too low at high isoprene levels –Need mechanism which results in net formation of OH instead of just recycling (Peeters et al. 2009)?

19. 19 Current and future Research Testing Peeters isoprene scheme –Impact on OH level –Reduce its uncertainties based on observational constrains (alkyl nitrates, methyl vinyl ketone, methacrolein) Investigation of new SOA precursors (Epoxide, MPAN) Smog chamber evaluation for low NO x conditions when additional source of data is available Model future emission scenarios