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Ying Xie 1 , Fabien Paulot 2 , Robert W. Pinder 1 , William P.L. Carter 3 ,

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 ,

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Ying Xie 1 , Fabien Paulot 2 , Robert W. Pinder 1 , William P.L. Carter 3 ,

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  1. Understanding the impact of isoprene nitrates and OH reformation on regional air quality using recent advances in isoprene photooxidation chemistry Ying Xie1, Fabien Paulot2, Robert W. Pinder1, William P.L. Carter3, Christopher G. Nolte1, Deborah J. Luecken1, William T. Hutzell1, Paul O. Wennberg2, and Ron Cohen4 1US EPA Office of Research & Development; 2California Institute of Technology; 3University of California Riverside; 4University of California Berkeley 9th Annual CMAS Conference Chapel Hill, NC

  2. Outline • Introduction • High NOx chemistry and isoprene nitrates • Low NOx chemistry and HOx recycling • Methodology • Results • Smog chamber evaluation • INTEX-NA 2004 • Conclusions • Current and future research

  3. ISOP + OH -> RO2 • ->RO + NO2 • formaldehyde, methyl vinyl ketone, methacrolein O3 RO2 + NO ->RNO3 yield (4 -15%)? terminal sinks or recycle NOx? Introduction • Isoprene is the predominant VOC • Global emissions ~500Tg/yr, oxidized within hours by OH • High NOx: NO • Low NOx: HO2/RO2 • High NOx:

  4. ISOP + OH -> RO2 • ->RO + NO2 • formaldehyde, methyl vinyl ketone, methacrolein O3 RO2 + NO ->RNO3 γ*secondary isoprene nitrates + (1- γ)*NO2 yield (4 -15%)? terminal sinks or recycle NOx? Introduction • Isoprene is the predominant VOC • Global emissions ~500Tg/yr, oxidized within hours by OH • High NOx: NO • Low NOx: HO2/RO2 • High NOx:

  5. ISOP + OH -> RO2 • ->RO + NO2 • formaldehyde, methyl vinyl ketone, methacrolein O3 RO2 + NO ->RNO3 γ*secondary isoprene nitrates + (1- γ)*NO2 Introduction • Isoprene is the predominant VOC • Global emissions ~500Tg/yr, oxidized within hours by OH • High NOx: NO • Low NOx: HO2/RO2 • High NOx: • Isoprene nitrates (INs) have large impact on O3 production • Increase INs yield by a factor 3 decrease global O3 production by 10% (Wu et al. 2007) • Represent a major uncertainty in determining the response of O3 to future changes in biogenic emissions • Wu et al. (2008a) found lack of sensitivity of O3 to climate change in southeastern US (12% INs , no NOx recycling) • Racherla and Adams (2006) reported a large O3 sensitivity for the same area (no INs)

  6. deposition INTEX Modeled Introduction • Low NOx: • Gap between modeled and measured OH levels ISOP + OH-> RO2 RO2 + HO2 ->ROOH (Ren et al. 2008)

  7. x x deposition INTEX Modeled Introduction • Low NOx: • Gap between modeled and measured OH levels ISOP + OH-> RO2 RO2 + HO2 ->ROOH (Ren et al. 2008)

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

  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 NOy • 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. Comparisons of the mechanisms

  11. Smog chamber evaluation • 34 experiments (UCR, UNC, CSIRO) covering ranges of VOC/NOx concentrations • 11 with initial NOx below 200 ppb • Results: • Higher and improved methyl vinyl ketone • Better O3 under NOx-limited conditions • Bias reduced from -14% to -5%

  12. NOx (ISOP – BASE) Layer 1, averaged over INTEX-NA isoprene NOx (isop > 300 ppt) formaldehyde CMAQ model evaluation – isoprene, formaldehyde, NOx

  13. Model evaluation – alkyl nitrates all data isop > 300 ppt

  14. 2-3 ppb increase 90th percentile Model evaluation – O3 ISOP – BASE Layer 1, averaged over INTEX-NA all data isop > 300 ppt

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

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

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

  18. Conclusions • Smog chamber study • Better methyl vinyl ketone • Better O3 • CMAQ simulation • Better Science • improvement in alkyl nitrates and almost all species • Slightly higher NOx and O3 concentrations due to more efficient NOx recycling • Improved O3 • more confidence in predicting the response of O3 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. 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 NOx conditions when additional source of data is available • Model future emission scenarios

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