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. O3O3 O2O2 O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CH 4, CO, VOCs NO 2 STRATOSPHERE TROPOSPHERE 8-18 km Tropospheric radical chemistry Air Quality Climate h h NO x = NO + NO 2 HO x = OH + HO 2

4. VOCs affect air quality and climate Isoprene Most important non-methane VOC Global emissions ~ methane (but > 10 4 times more reactive) ~ 6x anthropogenic VOC emissions

5. How we understand isoprene oxidation…ten years ago! OH Organic peroxy radicals NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds HO 2 Organic peroxides deposited Terminal sink for radicals Isoprene RO 2 ROOH RONO 2 OH is the main driver for isoprene oxidation! OH concentration can be modulated by isoprene. NO 2 O3O3 NO h

6. Part 1 : Uncertainties in OH concentrations

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

8. OH Organic peroxy radicals NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds HO 2 Organic peroxides deposited Terminal sink for radicals Isoprene RO 2 ROOH RONO 2 New understanding on the fate of organic peroxides + OH (Paulot et al., 2009, Science) Epoxide Epoxide is an important precursor for secondary organic aerosols. Regeneration of OH from epoxide was not enough to close the gap.

9. OH Organic peroxy radicals NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds HO 2 Organic peroxides Terminal sink for radicals Isoprene RO 2 ROOH RONO 2 + OH (Peeters et al., 2009, Phys. Chem. Chem. Phys.) The third pathway proposed by Peeters et al. – unimolecular isomerization! isomerization OH photolysis HPALD To match observed OH, isomerization needs to be much faster than other channels! Epoxide This was a theoretical prediction!

10. If the isomerization is fast, the impact on global OH is huge! (Taraborrelli et al., 2012, Nature Geoscience) this increases global OH by 14%, from 1.08 to 1.22 x 10 6 molecules cm -3. methane lifetime is reduced from 8.0 to 7.2 years. o Current observation-based estimate is 9.1 ± 0.9 years (Prather et al., 2012, GRL) OH + isoprene → n OH

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

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

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

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

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

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

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

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. OH Organic peroxy radicals NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds HO 2 Organic peroxides Terminal sink for radicals Isoprene RO 2 ROOH RONO 2 + OH isomerization OH photolysis HPALD Epoxide Uncertainties on ozone production

21. OH NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds Terminal sink for NO x and HO x Isoprene RO 2 RONO 2 NO 2 O3O3 NO h Competition between ozone production and suppression 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 NO x after degradation?

22. If these nitrates act as HNO3, they will be a sink for both NO x and HO x (0% recycling). If they react with OH/O 3 and release NO x, they will recycle NO x (100% recycling). The conclusion can differ by more than 10 ppb depending on different assumptions on the recycling efficiency. (Ito et al., 2009, JGR) Response of summer surface ozone to an increase in BVOC emissions caused by a 5K temperature increase…

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

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

25. What is so unique for Eastern US? (Millet et al., 2008, JGR) (Martin et al., 2008, AE) Surface NO x is mainly produced from anthropogenic activities HCHO is mainly produced from biogenic emissions (isoprene in particular) Anthropogenic + Natural

26. A new isoprene chemistry for global models (Mao et al., JGR, 2013) 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).

27. This chemistry was implemented in GEOS-Chem Ozone in the boundary layer during ICARTT 2004 Observations Model Obs vs. Model Improved O 3 -CO correlations due to: 1.Recycling of NO x from isoprene nitrates 2.HO 2 uptake (lower OH and increase NO x lifetime). (Mao et al., 2013, JGR)

28. Mean vertical profiles during ICARTT O 3 has no bias in boundary layer and free troposphere. HCHO provides good constraint on isoprene emissions. Observations Model (GEOS-Chem) (Mao et al., 2013, JGR)

29. Total alkyl nitrates (∑ANs) during ICARTT Model well reproduced ∑ANs. ∑ ANs is dominated by secondary organic nitrates (C3-C4). ∑ANs vs. HCHO∑ANs vs. O 3 Model well reproduced ∑ANs vs. HCHO and ∑ANs vs. O 3 correlations. These correlations cannot be reproduced by a fast isomerization channel of RO 2. Vertical profiles Speciation of ∑ANs (Mao et al., 2013, JGR)

30. NO y budget in eastern U.S. boundary layer for July 2004 SpeciesEmission Chemical (P-L) Dry Deposition Wet Deposition Net Export NO x 386-33744------5 PANs 2413------11 ∑ANs ANs 187.43.67 R 4 N 2 100.5-------10 HNO 3 277180110-3 Export of ∑ANs > Export of PANs (Mao et al., 2013, JGR)

31. New chemistry Previous studies without NO x recycling Current anthro NO x emissions (2004) Reduce current anthro NO x emissions by 50% Isoprene↑ NO x ↓ OH ↓ O 3 ↓ due to O 3 +ISOP Surface ozone response to isoprene emissions NO x emissions↓ Sensitivity of ozone to isoprene emissions ↓ (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. (Horowitz et al., 2007, JGR) (Mao et al., 2013, JGR) R4N2 is mainly produced at nightNO 3 oxidation dominates organic nitrate production All current models show that a large portion of daytime alkyl nitrates are from nighttime oxidation.

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

37. Part 4 : New effort on understanding BVOCs oxidation

38. Field studies over Southeast US in the summer of 2013 SENEX (NOAA) SOAS (NSF & EPA) NOMADSS (NCAR) Two aircrafts based at Smyrna, TN and a tower located at Centerville, Alabama. Measurements include VOC, NO x, ozone, aerosols, CCN etc. GFDL provided C180 nudge simulations to SENEX data archive. A modeling workshop to be held in GFDL this summer.

39. GFDL AM3 configuration for SENEX Fully coupled chemistry-climate model o Parameterizes aerosol activation into liquid cloud droplets o 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) C48 (200 x 200km) C180 (50 x 50km) Monthly mean ozone for July of 2012

40. NO x emissions has been reduced by 34% from 2005 to 2011 OMI NO 2 column in 2005 (summer) OMI NO 2 column in 2011 (summer) difference (Russell et al. 2012, ACP)

41. OH Organic peroxy radicals NO x ~10% ~90% Alkyl nitrates HCHO + MVK + MACR + other compounds HO 2 Organic peroxides Terminal sink for radicals Isoprene RO 2 ROOH RONO 2 + OH isomerization OH photolysis HPALD Epoxide Based on our current understanding… Can we see a shift from high NO x pathway to low NO x 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 fuel/industry open fires OH, O 3,NO 3 SOGSOA POA K vegetation fuel/industry open fires 700 isoprene terpenes oxygenates… 30 alkenes aromatics oxygenates… VOC EMISSIONPRIMARY EMISSION VOC 50 20100 20 Global sources in Tg C y -1 Two-product SOA ≡ secondary organic aerosol POA ≡ primary organic aerosol Aqueous reactions ? ? Uptake on aerosols

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

45. Thanks!

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