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Biogenic Hydrocarbons LectureAOSC 637

Atmospheric ChemistryRussell R. Dickerson

Finlayson-Pitts Chapt. 6 & 9 Seinfeld Chapt. 6

OUTLINEHistory

Nomenclature and structureSources and Sinks

Global Chemistry & TrendsRemaining Challenges

References

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.

Isoprene (C5H8)

Monoterpenes(C10H1

6)

Sesquiterpenes (C15H24)

WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?

Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller)

Three factors:1. Atmospheric Abundance2. Chemical reactivity3. The vapor pressure (or

volatility) of its products

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 %

Biogenic Hydrocarbons

Double bonds allow reactions with O3 and NO3 as well as OH

Ozone formation potential for terpenes in ~3 times that of butene. Butene: 10 NO2

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.

MAPPING OF VOC EMISSIONS FROM SPACEusing satellite measurements of HCHO columns

confirms dominance of biogenic over anthropogenic VOCs

COMPARING SOA POTENTIALS

Species Global (Tg/yr)

AromaticsBenzeneTolueneXyleneOther

21.75.86.74.54.7

SOA pot’l (15%) 3.2

Monoterpenes 130.6

SOA pot’l (10%) 13.1

Sesquiterpenes ?

SOA pot’l (75%) ?

Isoprene 341

SOA pot’l (3%) 10.2

EDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes)

What is the partitioning between ozone and SOA formation?

0MY

HC

Terpenoids: Griffin et al., 1999:Photo-oxidation: Y=1.6-84.5%NO3 oxidation: Y=12.5-89.1%O3 oxidation: Y=0-18.6%Isoprene: Kroll et al., 2005Photo-oxidation (OH): Y=0.9-3%Aromatics: Ng et al., 2007High NOx: Y=4-28%Low NOx: Y=30-36%

Published by AAAS

A. L. Robinson et al., Science 315, 1259 -1262 (2007)

This is what you get is you download directly from ScienceFig. 1. Partitioning data and volatility distribution of diesel POA measured at 300 K

Previous emissions studies overestimated Primary OA.

Effective Saturation Concentration

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

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).

Take Home Messages.

Biogenic VOC’s are highly reactive.

Isoprene is #10 in abundance but #1 in reactivity

They form O3 and CO in the presence of NOx.

They destroy O3 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.

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 H2 from the oxidation of hydrocarbon emissions from vegetation, Geophys. Res. Lett., 5, 679-682.