Jingqiu Mao (Princeton/GFDL)

1. Uncertainties in the atmospheric oxidation of biogenic volatile organic compounds (BVOCs) : implications for air quality and climate Jingqiu Mao (Princeton/GFDL) Yale University, 02/20/2014

2. Acknowledgement Measurements: William Brune (Penn State), Xinrong Ren (NOAA/UMD) Modeling: Fabien Paulot (Harvard), Daniel Jacob(Harvard), Ron Cohen (UC Berkeley), Paul Wennberg(Caltech), Larry Horowitz(GFDL) BEARPEX science team (Biosphere Effects on Aerosols and Photochemistry Experiment) ICARTT science team (International Consortium on Atmospheric Transport and Transformation) SENEX science team (Southeast Nexus)

3. Tropospheric radical chemistry Air Quality O2 hn O3 STRATOSPHERE Climate 8-18 km TROPOSPHERE hn NO2 NO O3 hn, H2O OH HO2 H2O2 CH4,CO, VOCs Deposition NOx = NO + NO2 HOx = OH + HO2

4. VOCs affect air quality and climate Isoprene Most important non-methane VOC Global emissions ~ methane (but > 104times more reactive) ~ 6x anthropogenic VOC emissions

5. How we understand isoprene oxidation…ten years ago! h O3 NO2 HCHO + MVK + MACR + other compounds ~90% NO ~10% NOx Terminal sink for radicals RONO2 OH RO2 Alkyl nitrates Isoprene Organic peroxy radicals HO2 deposited ROOH Terminal sink for radicals Organic peroxides • OH is the main driver for isoprene oxidation! • OH concentration can be modulated by isoprene.

6. Part 1 : Uncertainties in OH concentrations

7. Model underestimates measured OH by a factor of 2-10 in forested regions. Eastern US (isoprene-rich) Southern China (isoprene-rich) Pristine forests over South America (Lelieveld et al., Nature, 2008) (Ren et al., 2008, JGR) (Hofzumahaus, Science, 2009)

8. New understanding on the fate of organic peroxides HCHO + MVK + MACR + other compounds ~90% ~10% NOx Terminal sink for radicals RONO2 OH RO2 Alkyl nitrates Isoprene Organic peroxy radicals HO2 deposited ROOH Terminal sink for radicals Organic peroxides • Epoxide is an important precursor for secondary organic aerosols. • Regeneration of OH from epoxide was not enough to close the gap. + OH Epoxide (Paulot et al., 2009, Science)

9. The third pathway proposed by Peeters et al. – unimolecular isomerization! HCHO + MVK + MACR + other compounds ~90% ~10% NOx Terminal sink for radicals RONO2 OH RO2 Alkyl nitrates Isoprene Organic peroxy radicals HO2 ROOH + OH Organic peroxides isomerization Epoxide photolysis OH To match observed OH, isomerization needs to be much faster than other channels! HPALD This was a theoretical prediction! (Peeters et al., 2009, Phys. Chem. Chem. Phys.)

10. If the isomerization is fast, the impact on global OH is huge! OH + isoprene → n OH • this increases global OH by 14%, from 1.08 to 1.22 x 106 molecules cm-3. • methane lifetime is reduced from 8.0 to 7.2 years. • Current observation-based estimate is 9.1 ± 0.9 years (Prather et al., 2012, GRL) (Taraborrelli et al., 2012, Nature Geoscience)

11. Laboratory measurements show much slower rate of isomerization… Percentage of peroxy radicals going through isomerization (Crounse et al., 2011, PCCP) OH discrepancy still exists! (Wolfe et al., 2012, PCCP)

12. A new study – BEARPEX 2007/2009 Biosphere Effects on Aerosols and Photochemistry Experiment Bitter Experimentalists Always Repairing Pieces of Equipment eXperiment Located at the University of California Berkeley Blodgett Forest Research Station

13. OH measured by the traditional Laser induced fluorescence (LIF) method … Air OH cell Laser 308 nm Vacuum Pump change wavelength between on-line (OH fluorescence) to off-line (background) every 20 sec (called OHwave).

14. and also by a second method … Air OH scrubber OH cell Laser 308 nm Vacuum Pump • remove OH with an OH reactant (called chemical modulation or OHchem) every two minutes

15. The results were really shocking…! Traditional measured OH OH measured by the new method, “true” OH • The high OH measured in forests are likely biased due to some instrumental interference. • This interference is confirmed by other instruments. (Mao et al., 2012, ACP)

16. The interference signal increases with temperature, pointing to the evidence of BVOCs! Traditional measured OH OH measured by the new method, “true” OH Temperature (K) OH does not deplete at high temperature (high BVOCs), suggesting some level of OH recycling in the atmosphere. (Mao et al., 2012, ACP)

17. One possible candidate for causing this interference is Criegee Intermediate Criegee Intermediate is found to be ubiquitous in forests. (Mauldin et al. Nature, 2013)

18. Summary on OH uncertainties • OH discrepancy between measurements and modeling may be largely due to the instrumental inferences, likely from oxidation products from BVOCs. • OH recycling from isoprene oxidation does exist, but not as strong as theoretical study suggested.

19. Part 2: Uncertainties in ozone production

20. Uncertainties on ozone production HCHO + MVK + MACR + other compounds ~90% ~10% NOx Terminal sink for radicals RONO2 OH RO2 Alkyl nitrates Isoprene Organic peroxy radicals HO2 ROOH + OH Organic peroxides isomerization Epoxide photolysis OH HPALD

21. h O3 Competition between ozone production and suppression NO2 HCHO + MVK + MACR + other compounds ~90% NO ~10% NOx Terminal sink for NOx and HOx RONO2 OH RO2 Alkyl nitrates Isoprene • Major uncertainties lie in two aspects: • How much RONO2 is produced, experimental results vary from 4% to 12%. • What is fate of RONO2? Will they release NOxafter degradation?

22. Response of summer surface ozone to an increase in BVOC emissions caused by a 5K temperature increase… If these nitrates act as HNO3, they will be a sink for both NOx and HOx (0% recycling). If they react with OH/O3 and release NOx, they will recycle NOx (100% recycling). The conclusion can differ by more than 10 ppb depending on different assumptions on the recycling efficiency. (Ito et al., 2009, JGR)

23. First generation of isoprene nitrates degraded to second generation nitrates! First generation isoprene nitrates (C5) Laboratory measurements show that recycling efficiency is around 55%! Second generation isoprene nitrates (C3-C4) (Paulot et al., 2009, ACP)

24. The International Consortium on Atmospheric Transport and Transformation (ICARTT) aircraft study: July-August 2004 Chemical transport model (GEOS-Chem) Extensive measurements on isoprene oxidation products, including total alkyl nitrates (∑ANs)

25. What is so unique for Eastern US? Anthropogenic + Natural HCHO is mainly produced from biogenic emissions (isoprene in particular) Surface NOx is mainly produced from anthropogenic activities (Martin et al., 2008, AE) (Millet et al., 2008, JGR)

26. A new isoprene chemistry for global models ISOPO2 + NO is based on Paulot et al. (2009, ACP). ISOPO2 + HO2 is based on Paulot et al. (2009, Science). Isomerization of ISOPO2 is based on Peeters et al. (2009, PCCP) and Crounse et al. (2011, PCCP) . (Mao et al., JGR, 2013)

27. This chemistry was implemented in GEOS-Chem Ozone in the boundary layer during ICARTT 2004 Model Observations Obs vs. Model Improved O3-CO correlations due to: Recycling of NOx from isoprene nitrates HO2 uptake (lower OH and increase NOx lifetime). (Mao et al., 2013, JGR)

28. Observations Model (GEOS-Chem) Mean vertical profiles during ICARTT O3 has no bias in boundary layer and free troposphere. HCHO provides good constraint on isoprene emissions. (Mao et al., 2013, JGR)

29. Total alkyl nitrates (∑ANs) during ICARTT Vertical profiles Speciation of ∑ANs Model well reproduced ∑ANs. ∑ ANs is dominated by secondary organic nitrates (C3-C4). ∑ANs vs. HCHO ∑ANs vs. O3 Model well reproduced ∑ANs vs. HCHO and ∑ANs vs. O3 correlations. These correlations cannot be reproduced by a fast isomerization channel of RO2. (Mao et al., 2013, JGR)

30. NOy budget in eastern U.S. boundary layer for July 2004 Export of ∑ANs > Export of PANs (Mao et al., 2013, JGR)

31. Surface ozone response to isoprene emissions NOx emissions↓ Sensitivity of ozone to isoprene emissions ↓ New chemistry Isoprene↑ NOx ↓ OH ↓ O3 ↓ due to O3+ISOP Previous studies without NOx recycling Reduce current anthroNOx emissions by 50% Current anthroNOx emissions (2004) (Mao et al., 2013, JGR)

32. Summary on ozone uncertainties • Current best estimate of isoprene nitrate yield is 12%, with ~50% recycling efficiency of NOx. • This results in a positive dependence of ozone on isoprene emissions throughout the U.S. • Good agreement between observed and modeled total alkyl nitrates provides additional evidence on the isomerization rates.

33. Part 3: Uncertainties in nighttime chemistry

34. Nighttime chemistry Nighttime yield of organic nitrates is 70%>> daytime yield (11.7%)

35. NO3 oxidation dominates organic nitrate production R4N2 is mainly produced at night (Mao et al., 2013, JGR) (Horowitz et al., 2007, JGR) All current models show that a large portion of daytime alkyl nitrates are from nighttime oxidation.

36. Sunset Sunrise How does nighttime chemistry affect global nitrogen/ozone budget? Entrainment zone Boundary layer structure by Stull (1988).

37. Part 4 : New effort on understanding BVOCs oxidation

38. Field studies over Southeast US in the summer of 2013 SENEX (NOAA) Two aircrafts based at Smyrna, TN and a tower located at Centerville, Alabama. Measurements include VOC, NOx, ozone, aerosols, CCN etc. GFDL provided C180 nudge simulations to SENEX data archive. A modeling workshop to be held in GFDL this summer. NOMADSS (NCAR) SOAS (NSF & EPA)

39. GFDL AM3 configuration for SENEX • Fully coupled chemistry-climate model • Parameterizes aerosol activation into liquid cloud droplets • solves both tropospheric and stratospheric chemistry over the full domain • Nudging wind with GFS meteorological field • High resolution (50 x 50 km) and coarse resolution (200 x 200 km) • MEGAN biogenic emissions (process-based emission) • Anthropogenic emissions use RCP 8.5 scenario (0.5 x 0.5 degree) • New isoprene chemistry (Mao et al., 2013 JGR) C180 (50 x 50km) C48 (200 x 200km) Monthly mean ozone for July of 2012

40. NOx emissions has been reduced by 34% from 2005 to 2011 OMI NO2 column in 2005 (summer) OMI NO2 column in 2011 (summer) difference (Russell et al. 2012, ACP)

41. Based on our current understanding… HCHO + MVK + MACR + other compounds ~90% ~10% NOx Terminal sink for radicals RONO2 OH RO2 Alkyl nitrates Isoprene Organic peroxy radicals HO2 ROOH + OH Organic peroxides isomerization Epoxide photolysis OH HPALD Can we see a shift from high NOx pathway to low NOx pathways? Would that mean we will have more SOA with the reduction of NOx?

42. SENEX (Southeast) flight track Preliminary model results

43. Next step: Organic aerosols over Southeast US Global sources in Tg C y-1 20 K OH, O3,NO3 SOG SOA VOC Two-product ? POA Aqueous reactions isoprene terpenes oxygenates… ? 50 Uptake on aerosols 20 100 700 alkenes aromatics oxygenates… 30 vegetation fuel/industry open fires fuel/industry open fires VOC EMISSION PRIMARY EMISSION SOA ≡ secondary organic aerosol POA ≡ primary organic aerosol

44. Temperature trend over past century 1950-2006 for May-June (Unit: K/Decade) 1930-1990 change in Annual Mean Surface Temperature (Leibensperger et al., 2012, ACP) Current hypothesis: this warming hole is, at least partially, due to the secondary organic aerosols over the eastern US(Goldstein et al., 2009, PNAS). This temperature trend cannot be explained by the change in precipitation or dynamic patterns (El Niňo, NAO) (Portmann et al., 2009, PNAS).

45. Thanks!

46. Model of Emission of Gases and Aerosols from Nature (MEGAN) • Process-based emission inventory Leaf age Leaf Area Index Temperature dependence Light dependence Fractional coverage Emission factor