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Chemistry of NO x and SOA: VOC Oxidation by Nitrate Radicals

Chemistry of NO x and SOA: VOC Oxidation by Nitrate Radicals. Andrew Rollins Cohen research group, department of chemistry University of California, Berkeley, USA. NO x = NO + NO 2. O 2. O 3. h ν. Τ s.s. ~ minutes. NO. NO 2. O 2. O 3. OH, O 3. Aerosol Surface Area. SOA.

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Chemistry of NO x and SOA: VOC Oxidation by Nitrate Radicals

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  1. Chemistry of NOx and SOA:VOC Oxidation by Nitrate Radicals Andrew Rollins Cohen research group, department of chemistry University of California, Berkeley, USA

  2. NOx = NO + NO2 O2 O3 hν Τs.s. ~ minutes NO NO2 O2 O3

  3. OH, O3 Aerosol Surface Area SOA IPCC AR4

  4. Regional NOx Emission trends Measured Göteborg NO2 Estimates for total Asian emissions van Aardenne et al., Atmospheric Environment 33 (1999) 633Ð646

  5. outline • Motivations • Global/Regional changes in NOx:VOC emissions • NOx emissions as control strategy • 2 classes of NOx effects on SOA production • Product distributions / RO2 chemistry • NO3 + VOC → SOA • Nitrate Radical (NO3) • Isoprene + NO3 SAPHIR experiment • Alkyl Nitrate kinetic uptake experiments

  6. SOA NOx Dependence: effects on peroxy radical chemistry RO2 + HO2 vs RO2 + NO High NOx and VOC High NOx and VOC Unexplained / not always observed Kroll et al. Environ. Sci. Technol. 2006, 40, 1869-1877 Presto et al. Environ. Sci. Technol. 2005, 39, 7046-7054

  7. Nitrate Radical (NO3)

  8. Nitrate Radical (NO3)

  9. Nitrate Radical (NO3) Sunset [NO3]≈10’s ppt Brown et al 2004

  10. NO3 vs OH and O3 as VOC sinks 0.5 x 107 cm-3 = 0.2 ppt OH 20 ppt NO3 Brown et al 2004

  11. Blodgett Forest Research Station (Sierra Nevada Mountains, California) Summer 2007 average • Decreased but significant [BVOC] remain at night. • Isoprene emissions increase with temperature and light: ~10% isoprene processed by NO3. • Products of daytime oxidation persist with high concentrations throughout the night.

  12. Alkene Oxidation by Nitrate Radicals • Decrease in vapor pressure of parent molecule upon addition of nitrate group is comparable to products of reaction with OH. • NO3 reactions dominate at night: lower temperatures, decreased boundary layer / increased concentrations. J.H. Kroll, J.H. Seinfeld / Atmospheric Environment 42 (2008) 3593–3624

  13. Jϋlich chamber experiments • SAPHIR chamber ~ 260 m3. • Near Ambient NOx & VOC • Long chamber runs (> 12 hours) • NO3 SOA experiments: • Linomene • Β-Pinene (high and low RH) • Isoprene (seeded)

  14. Isoprene + NO3 • 15 hour run • Max 10 ppb isoprene, 30 ppb NO2, 60 ppb O3 • NH3(SO4)2 seed • AMS, SMPS, PTRMS, GC, TDLIF • Many NO3 / N2O5 measurements

  15. Isoprene C5H8 • 440-6601 TgC / ~13002 TgC total non-methane VOC (biogenic + anthropogenic) ≈ 34 – 50% total carbon. • Two double bonds/ multiple oxidation steps / high reactivity to OH, O3, NO3. • Isoprene SOA potential is poorly understood, small yields of SOA (5% by NO3) could be large Fractions of total global SOA annual production (2-3 TgC / 12-70TgC)4 • Early OH and O3 experiments (100s of ppbs isoprene and NOx) concluded Isoprene not an SOA precursor, because 1st generation oxidation products of isoprene are too volatile. More recently photochemical experiments demonstrate that Isoprene possibly contributes up to 47%5 of global SOA, by polymerization and heterogeneous chemistry of initial oxidation products • Alkyl Nitrate formation by addition of NO3 observed with high (80%) yields, increase MW and adding functionality. SOA yields reported at 4.3% - 23.8% (increasing with existing OM).6 4Kanakidou et al. 2005 5Zhang et al. 2007 6Ng et al. 2008 1Guenther et al. 2006 2Goldstein and Galbally 2007 3Calvert et al. 2000

  16. 3-4% 70-80% 3-4% Isoprene + NO3 Products

  17. Chamber Experiment Additions < 10% of isoprene consumed by O3

  18. SOA from: • NO3 + initial oxidation products? • RO2 + RO2 vs RO2 + NO3?

  19. Chamber RO2 fate RO2 + NO3 not expected to produce Less volatile products than RO2 + RO2

  20. Modeling Chemistry NO3 kfit Second generation oxidation produts

  21. Role of secondary chemistry NO3 NO3 Isoprene → X → Y 2% Yield Secondary oxidation products Initial oxidation products

  22. Role of secondary chemistry NO3 NO3 Isoprene → X → Y 2 0% Yield 10% Yield Secondary oxidation products Initial oxidation products

  23. Importance of NO3 / nighttime oxidation SAPHIR Ambient Apel et al 2002, JGR VOL. 107, NO. D3, 10.1029/2000JD000225

  24. 3-4% 70-80% 3-4% Aerosol Composition NO3 NO3 NO3 RO2 NO3 Observed SOA Composition polymerization, decomposition

  25. High correlation between AMS nitrate, AMS organic and total alkyl nitrates signals indicates condensation of organic nitrate is responsible for majority of SOA High initial yield of nitrate formation from initial reaction Total mass observed requires SOA by oxidation of one of the organic nitrate products of isoprene + NO3, not just MVK and MACR. Aerosol Composition

  26. AMS indicates 15% mass is nitrate mass High yield of nitrates from initial rxn and correlation of nitrate formation with SOA suggest multiple NO3 additions lead to aerosol. 2 observations indicate underestimation of aerosol nitrate, or NOx release upon SOA condensation

  27. Thermal Dissociation Laser Induced Fluorescence of Aerosol Nitrates • Thermal desorption of semivolatiles • Thermal dissociation of nitrates: • LIF detection of NO2 • Measurements of total aerosol bound nitrate mass in: • HNO3 • Organic Nitrates

  28. TD-LIF Aerosol Organic Nitrate Remove gas phase NOy, pass aerosol • Coupled to entrained aerosol flow tube for measurement of uptake coefficients

  29. Pneumatic Nebulizer, (NH4)2SO4 droplets NOy Bubbler Diffusion Dryer Entrained Aerosol Flow Tube

  30. HNO3 on NH3(SO4)2 particles ω = 34100 cm/s A = 5 x 10-3 cm2/cm3 γ = 0.006

  31. Uptake of synthesized organic nitrates • Salts • Organic particles

  32. NOx / Aerosol Research Questions • Effects of changing NOx / VOC emissions on the total SOA production, and speciation. • Total yield changes? • Aerosol composition? If composition, is CCN affected? • Current research: • Chamber SOA and organic nitrate aerosol yields / mechanisms from NO3 oxidation of BVOC’s. • Flow tube uptake measurements of organic nitrates / nitric acid on aerosol surfaces.

  33. Take Home Points • Regulation of NOx emissions is a primary control strategy and we should expect NOx / VOC ratios will change with significant regional differences. • NO3 chemistry important for producing higher MW organics, is active at night when concentrations of primary VOC’s are lower compared to oxidation products providing an increased opportunity for multiple oxidation steps, temperatures are lower. • Yields for SOA produced from VOC’s requiring multiple oxidations to achieve low enough vapor pressure for condensation may be underestimated.

  34. Cohen Group Juliane Fry (Reed College, Oregon) Ronald Cohen Paul Wooldridge F.Z. Jϋlich scientists Astrid Kiendler-Scharr Steve Brown, Hendrik Fuchs, Bill Dubé (NOAA) Sarpong Group (UCB) Walter Singaram Massoud Motamed Thanks to…

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