Transcript Lecture #21 (ppt) Biogenic hydrocarbons

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
1
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.
WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?
Isoprene (C5H8)
Monoterpenes(C10H16)
Three factors:
1. Atmospheric Abundance
2. Chemical reactivity
3. The vapor pressure (or
volatility) of its products
Sesquiterpenes (C15H24)
Anthropogenic SOA-precursors =
aromatics (emissions are 10x smaller)
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
MAPPING OF VOC EMISSIONS FROM SPACE
using satellite measurements of HCHO columns
confirms dominance of biogenic over anthropogenic VOCs
COMPARING SOA POTENTIALS
EDGAR 1990 Emissions (Aromatics)
and GEIA (Isoprene/Monoterpenes)
Species
Global (Tg/yr)
Aromatics
Benzene
Toluene
Xylene
Other
21.7
5.8
6.7
4.5
4.7
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
What is the partitioning between ozone and SOA formation?
M 0
Y
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., 2005
Photo-oxidation (OH): Y=0.9-3%
Aromatics: Ng et al., 2007
High NOx: Y=4-28%
Low NOx: Y=30-36%
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
A. L. Robinson et al., Science 315, 1259 -1262 (2007)
Published by AAAS
Previous emissions studies overestimated Primary OA.
Effective Saturation Concentration
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
A. L. Robinson et al., Science 315, 1259 -1262 (2007)
Published by AAAS
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).
A. L. Robinson et al., Science 315, 1259 -1262 (2007)
Published by AAAS
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, 14731474.
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.