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Insights into Biogenic Volatile Organic Compounds Emissions and Products

Explore emission characteristics and modeling of biogenic compounds, including terpenes and oxygenated VOCs, for better air quality understanding. Learn about their reactions and secondary organic aerosol formation.

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Insights into Biogenic Volatile Organic Compounds Emissions and Products

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  1. Review of Biogenic Volatile Organic Compounds and Their Products Brian Lamb(1), Daniel Grosjean(2), Betty K. Pun(3), and Christian Seigneur(3) Biogenic Day 9-10 December 1999 (1) Washington State University, Pullman, WA (2) DGA, Inc., Ventura, CA (3) AER, San Ramon, CA

  2. Condensable products Emissions Atmospheric reactions Gas/particle partition PM O3 Introduction Biogenic compounds are precursors to ozone (O3) and particulate matter (PM)

  3. Biogenic Volatile Organic Compounds Emission % in North America • Isoprene 31% • Methylbutenol (MBO) 5% • Monoterpenes + sesquiterpenes 22% • Reactive oxygenates 16% • Less reactive oxygenates 26%

  4. Isoprene • Sampling, analytical, eddy covariance flux methods are well-developed Emission Characteristics • Dominant VOC • From deciduous species and spruce • During day-light hours only • Depends on leaf temperature and PAR

  5. Isoprene Data Needs • Vegetation types other than oaks, poplars, aspen, and spruce • Effects of temperature history and season • Landcover data

  6. Monoterpenes • Predominant compounds: a-, b-pinene, limonene, and D3-carene Emission Characteristics • From conifers and some deciduous species • Depends on temperature • Some Mediterranean oaks emit terpenes with isoprene-like light, temperature dependence

  7. Monoterpene Data Needs • Emission capacities of individual monoterpene compounds • Characterization of emission response to • rainfall / humidity • herbivory • Canopy-scale measurements • Comparison of measurements and inventory models

  8. Sesquiterpenes • Semivolatile, low emission capacities • May contribute up to 16% of total BVOC landscape-scale flux Data Needs • Identification of individual sesquiterpenes and their emission capacities • Canopy-scale measurements • Regional emissions estimates

  9. Oxygenated VOC • Methylbutenol, emitted via the light-dependent chloroplast mechanism • Other oxygenates emitted by defense mechanisms or cut and drying vegetation • Regional emissions difficult to quantify due to intermittent emissions • No canopy-scale information • No evaluation at landscape scale

  10. Biogenic Emissions Modeling e = area-average emission capacity D = foliar density g = activity factor for light, temperature, leaf age d = activity factor for other factors r = canopy escape efficiency

  11. Canopy Modeling • Microclimate within a forest canopy as a function of height • temperature (heat flux) • PAR

  12. Measurements and Modeling (Isoprene) • Measurement scale-up studies • 40% difference between leaf and canopy scales • Reconciliation of measurements with models • 30% difference between flux measurement and model for site specific applications • factor of 1.2 to 2 using inverse modeling of ambient concentrations

  13. Chemical Functionality • Saturated aliphatics • Alkanes, alcohols, aldehydes, ketones, acids, esters, ethers • Aromatics • Unsaturated Aliphatics • Alkenes, dienes, terpenes (1 to 3 C=C), sesquiterpenes (1 to 3 C=C) • Unsaturated Oxygenates • alcohols, esters, aldehydes, ketones

  14. Kinetics of Saturated Aliphatics and Aromatics • Saturated aliphatics react only with OH • Aromatics react mainly with OH, NO3 may be a minor pathway • Missing kinetic data for hexanal, camphor, cineole, and p-cymene can be estimated by structure-reactivity relationships • Acetone has the maximum t1/2(1) = 36 days • Hexanal has the minimum t1/2(1) = 6 hours (1) OH = 106 molec/cm3

  15. Kinetics of Unsaturated Compounds Unsaturated VOC react with OH, O3, and NO3 t1/2,OH(1) (hours) t1/2, O3(2) (hours) alkenes 3.0 - 23 1.3 - 160 isoprene 1.9 20 terpenes 0.53 - 3.6 0.01 - 280 sesquiterpenes 0.65 - 4.1 0.02 - >500 oxygenates 1.2 - 6.6 0.60 - 130 (1) OH = 106 molec/cm3; (2) O3 = 30 ppb

  16. Highly Reactive Compounds a-terpinene a-humulene Linalool Reaction with O3 may be the dominant removal process for the more reactive BVOC

  17. First-Generation Products • Example: OH + a-pinene • Pinonaldehyde, acetone, formaldehyde • Organic nitrates, hydroxy nitrates, dihydroxy nitrates, dihydroxycarbonyls • For O3 and OH reactions • Detailed information for alkenes, a-, and b-pinene, and unsaturated alcohols • Limited or no information for >20 BVOC • Less information on NO3 reaction

  18. SOA Formation • 14 BVOC known to form SOA • 10 terpenes (a-pinene most studied) • 2 sesquiterpenes • 2 unsaturated alcohols • Isoprene does not form SOA • SOA composition studied for 5 BVOC (reactions with O3 and OH only): a-, b-pinene, d-limonene, terpinolene, D3-carene

  19. Reactions of First-Generation Products • Kinetic data for first-generation products are limited • Aldehydes removed rapidly by OH reaction • Unsaturated carbonyls react with O3 • Product studies conducted for only 6 first-generation compounds • Very limited information on second-generation products

  20. Detailed BVOC Mechanisms • With the exception of isoprene and a-pinene, detailed mechanisms cannot be constructed for BVOC

  21. CH3CH2 CH2CH2OH + OH C = C H H · CH3CH2CH CHCH2CH2OH OH HO2 NONO2 CH3CH2CH(OH)CCH2CH2OH O + HO2 O3 O · CH3CH2CHOH + HCCH2CH2OH O2 HO2 O CH3CH2CHO HO2 + HOCH2CH2CH(OH)CCH2CH2OH O3 Formation from BVOC · CH3CH2CHCHCH2CH2OH OH NO2 NO2 O2, NO O2, NO CH3CH2CHCH(OH)CH2CH2OH CH3CH2CH(OH)CHCH2CH2OH O O · · Isom. + O2 u.d. · CH2CH2CH(OH)CH(OH)CH2CH2OH NO2 O2, NO · OCH2CH2CH(OH)CH(OH)CH2CH2OH Isom. · HOCH2CH2CH(OH)C(OH)CH2CH2OH O2

  22. Organic Aerosol Partition Theories • Saturation • Fixed yield approach • Absorption into an organic phase • Aqueous dissolution Total concentration (Ctot) Cgas = Psat Cparticle = Ctot - Psat Psat Gas phase only Cgas = Ctot K Cparticle Cgas H Cparticle Cgas

  23. Existing SOA Modules

  24. OC (g) OC (aq) OC (g) OC (l) Modules Under Development • Externally Mixed Aerosols • Surrogate Species Type A (Aqueous) Type B (Organic) e.g., Malic acid, e.g., Octadecanoic acid Glyoxalic acid

  25. Data Needs Chemistry • Products studies • Mechanisms • SOA composition SOA Partition Emissions • Identity of SOA species • Theoretical development • Individual terpene species • Sesquiterpenes and oxygenates • Need instrument development work

  26. Acknowledgement This work is funded by the Coordinating Research Council (CRC), Contract Number A-23

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