1. 1 Biogenic Hydrocarbons Lecture AOSC 637 Atmospheric Chemistry Russell R. Dickerson Finlayson-Pitts Chapt. 6 & 9 Seinfeld Chapt. 6 OUTLINE History Nomenclature and structure Sources and Sinks Global Chemistry & Trends Remaining Challenges References

2. Biogenic hydrocarbons History Zimmerman et al., (1978) showed that oxidation of VOC’s, especially isoprene produces CO. Chameides et al., (1988) showed that isoprene dominates the VOC chemistry of smog in Atlanta. But removal of trees makes smog worse. Robinson et al., (2007) showed that most of the organic aerosol in the troposphere is secondary.

3. Isoprene (C 5 H 8 ) Monoterpenes(C 10 H 16 ) Sesquiterpenes (C 15 H 24 ) WHICH VOC’s ARE IMPORTANT SOA PRECURSORS? Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller) Three factors: 1.Atmospheric Abundance 2.Chemical reactivity 3.The vapor pressure (or volatility) of its products

4. Biogenic Hydrocarbons Roughly 400 organic compounds are known to be emitted by plants. Most abundant are terpenes  Isoprene and various isoprene dimers called monoterpenes Pine emissions: 20% 21.5% 42 %

5. Biogenic Hydrocarbons Double bonds allow reactions with O 3 and NO 3 as well as OH Ozone formation potential for terpenes in ~3 times that of butene.  Butene: 10 NO 2  Terpenes have the potential to make 30 ozone per molecule! Total U.S. emissions of terpenes is ~ 20 Tg/yr. Emissions related to temp and soil moisture.

6. MAPPING OF VOC EMISSIONS FROM SPACE using satellite measurements of HCHO columns confirms dominance of biogenic over anthropogenic VOCs

7. COMPARING SOA POTENTIALS SpeciesGlobal (Tg/yr) Aromatics Benzene Toluene Xylene Other 21.7 5.8 6.7 4.5 4.7 SOA pot’l (15%)3.2 Monoterpenes130.6 SOA pot’l (10%)13.1 Sesquiterpenes? SOA pot’l (75%)? Isoprene341 SOA pot’l (3%)10.2 EDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes)

8. What is the partitioning between ozone and SOA formation? Terpenoids: Griffin et al., 1999: Photo-oxidation: Y=1.6-84.5% NO 3 oxidation: Y=12.5-89.1% O 3 oxidation: Y=0-18.6% Isoprene: Kroll et al., 2005 Photo-oxidation (OH): Y=0.9-3% Aromatics: Ng et al., 2007 High NOx: Y=4-28% Low NOx: Y=30-36%

9. Published by AAAS A. L. Robinson et al., Science 315, 1259 -1262 (2007) This is what you get is you download directly from Science Fig. 1. Partitioning data and volatility distribution of diesel POA measured at 300 K

10. Previous emissions studies overestimated Primary OA.

11. Effective Saturation Concentration

12. Published by AAAS A. L. Robinson et al., Science 315, 1259 -1262 (2007) Fig. 3. Maps of predicted ground-level OA concentrations for four PMCAMx simulations: (A) a traditional model with nonvolatile POA emissions and (B to D) three simulations that account for the partitioning of primary emissions--one assuming nonreactive emissions and two considering photochemical aging

13. Published by AAAS A. L. Robinson et al., Science 315, 1259 -1262 (2007) Fig. 4. Predicted changes in the POA/SOA split and total OA between the current framework and the revised model (results shown in Fig. 3).

14. Take Home Messages. Biogenic VOC’s are highly reactive. Isoprene is #10 in abundance but #1 in reactivity They form O 3 and CO in the presence of NOx. They destroy O 3 in the absence of NOx. Their concentration is greatest in daylight hours. They form Secondary Organic Aerosols (SOA). Lifetime is so short that budgets are most uncertain.

15. References Chameides, W. L., R. W. Lindsay, J. Richardson, and C. S. Kiang (1988), The role of biogenic hydrocarbons in urban photochemical smog: Atlanta as a case study, Science, 241, 1473- 1474. Guenther, A., C. N. Hewitt, D. Erickson, R. Fall, C. Geron, T. Graedel, P. Harley, L. Klinger, M. Lerdau, W. A. McKay, T. Pierce, B. Scholes, R. Steinbrecher, R. Tallamraju, J. Taylor, and P. Zimmerman (1995), A Global-Model of Natural Volatile Organic-Compound Emissions, Journal of Geophysical Research-Atmospheres, 100, 8873-8892. Robinson, A. L., N. M. Donahue, M. K. Shrivastava, E. A. Weitkamp, A. M. Sage, A. P. Grieshop, T. E. Lane, J. R. Pierce, and S. N. Pandis (2007), Rethinking organic aerosols: Semivolatile emissions and photochemical aging, Science, 315, 1259-1262. Zimmerman, P. R., R. B. Chatfield, J. Fishman, P. J. Crutzen, and P. L. Hanst (1978), Estimates of the production of CO and H 2 from the oxidation of hydrocarbon emissions from vegetation, Geophys. Res. Lett., 5, 679-682.