What are the precursor compounds for secondary organic aerosols? What are the types of vegetation, vehicle exhaust, and burning that emit these precursors and under what conditions?

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What are the precursor compounds for secondary
organic aerosols? What are the types of
vegetation, vehicle exhaust, and burning that
emit these precursors and under what
conditions? R.Kamens, M. Jang, S. Lee, M.
Jaoui, Depart. of Environ. Sci. and Eng.
UNC-Chapel Hill kamens_at_unc.edu
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Secondary organic aerosol (SOA) material may be
defined as organic compounds that reside in the
aerosol phase as a function of atmospheric
reactions that occur in either the gas or
particle phases.
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• The relative importance of precursors to
  secondary aerosol formation will depend on
• overall aerosol potential
• atmospheric emissions
• presence of other initiating reactants (O3, OH,
  NO3, sunlight, acid catalysts)

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1. Terpenoid 2. Aromatic 3. Particle Phase
Reactions (aldehydes and alcohols)
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Leonardo Da Vinvi described blue haze and thought
that plant emissions were its source(Went,
1959) Da Vinvi believed that it was due to water
moisture emitted from the plants
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F.W.Went published papers on biogenic emissions
from vegetation over 40 years ago. He posed the
question, what happens to 17.5x107 tons of
terpene-like hydrocarbons or slightly oxygenated
hydrocarbons once they are in the
atmosphere? Went suggested that terpenes are
removed from the atmosphere by reaction with
ozone and demonstrated blue haze formation by
adding crushed pine or fir needles to a jar with
dilute ozone.
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Different Terpene structures

a-pinene
b-pinene
myrcene

d-limonene



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Synthesis of Terpenes From CO2 Ruzika, 1953 No
mechanism for isoprene storage While terpenes
can stored in resin duct
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Global VOC Emissions Rates Estimates Guenther et
al, 1995 (Tg/y) Isoprene Monoterpenes
ORVOC Total VOC Woods 372 95 177
821 Crops 34 6 45 120 Shrub
103 25 33 194 Ocean 0 0
2.5 5 Other 4 1
2 9 All 503 127 260 1150
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Ambient Concentrations of selected terpenes
(pptV)
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Aerosol concentrations of selected terpenes
products (ng m-3) 1ng m-3 0.1pptV
Yu et al. Kavouras et al, 1998 Pinic
acid 0.5 0.4- 85 pinonic acid 0.8 9
- 141 norpinonic acid 0.1-
38 Pinonaldehyde 1.0 0.2- 32 hydroxy-pinonal
dehydes 0.5 oxo-liminoic acid 0.8 Nopinone 133
0.0 - 13
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Mechanisms can often explain the formation of
products
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Sesquiterpenes (C15H24)
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Sesquiterpenes (C15H24) There is a dearth of
data on the emissions strength of sesquesterpenes
compared to terpenes May contribute as much as
9 to the total biogenic emissions from plants.
(Helmig ,et al, 1994)
Flux data, Atlanta forest, Helmig et al., 1999
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Lifetimes of Sesquiterpenes
average OH concentration 1.6x106 NO3 5x108
for 12 hours of night time O3 7x1011
(molecules cm-3)
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Fluxes computed with and w/o an ozone scrubber
(50 ppb of O3 w/o O3 scrubber) over Fuentes, et
al. 2000)
Limonene

Caryophylene
with
w/o
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Other emissions (Winer et al. , Kesselmeier and
Staudt )
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Factors that influence emissions
1. Temperature 2. light 3. injury
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b-pinene emission rates per gram of dry biomass
as a function of temperature (Fuentes, et al.
2000)
E Es exp b (T-Ts) Tingy et al.

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a-pinene emissions compared to temp, and CO2
exchange (Mediterranean Oak, Kesselmeire et al )
a-pinene
temp

CO2 exchange
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Changes in relative humidity were generally not
deemed to be an important factor affecting
terpene emissions (Guenther, JGR,1991)A young
orange tree was exposed to drought stress by
withholding water. Emissions of b-caryophyllene
and trans-b-ocimene decreased little (-6) from
the non-drought conditions. Hansen and
Seufert,(1999).

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Emissions from drought-stressed apple leaves
seem to show significant increases in hexanal,
2-hexenal, and hexanol (Ebel et al.
1995)Shade,et al (G. Res. Let.,1999) measured
increases in monoterpene emissions of D-3 carene
over a ponderosa pine plantation in the Sierra
Nevada mountains after rain events and under high
humidity, Tingey equation is corrected by
multiplying by a relative humidity factor,
BET. BET cxRHn)/((1-cRHn)x(1(c-1)xRHn)
where
c a constant, and RHn a normalized relative
humidity (relative humididy-18)/82

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Emissions from damaged leaves contain
C6-aldehydes and alcohols.Temporary increases
in terpene emissions have been observed from
mounting plants in chambers.Isoprene emissions
seem unaffected by plant damage. Injury to the
bark of pine trees increases terpene emissions.
Fungal attack on lodgepole pines releases
terpenes and high amounts of ethanol, thought to
attract pine beetles.
Plant damage

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Global terpene sources (Tg/y)
Tropical forest 22
Grass/shrubs/hot 22
savanna 13
Tropical rain forest 11
Conifers and evergreens 20
Deciduous 7
Re-growing woods 7
Marsh/swamp/bogs 2
Crops/woods-warm 3
tundra 0.4
desert 1
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Aerosol formation from Terpenes

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Aerosol potential (Odum theory)

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Formation of pinic acid
Scheme 2
C
diacid
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COOH
H
O
COOH
2
A
Pinalic acid
-CH
OH
3
Pinic acid

O
OH
C
3
Criegee2
HO
2
D

-
OH
-
OH
CHO
O
-HCHO
O
OH
2
CHO
O
O
oxo-pinonaldehyde
OH,O
,HO
2
2
CHO
COOH
O
-O
3
OH
OH
hydroxypinonic acid
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Rates that Gases enter and leave the particle

• Kp kon/koff
• koff ? e -Ea/RT

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0.95 ppm a-pinene 0. 44ppm NOx
model
data
NO
O3
NO2
NO2
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Measured particle mass vs. model
reacted a-pinene
data
model
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particle phase pinonaldehye
data
model
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Aerosol potential (Odum theory)

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Griffin et al. biogenic aerosol yields
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Relative aerosol potential of terpenoids
Andersson-Sköld and Simpson, JGR, 2001

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Used a global photochemcial model to estimate the
amount of terpenes and other biogenics that are
reacted, DROGi.These were used in conjunction
with specific compound Odum fitting constants
to estimate total boigenic aerosol production on
a yearly basis.This may be a conservative
estimate because the fitting contents are derived
at 308K, does not consider other aerosol
surfaces, or particle phase reactions
Griffin et al, JGR, 2000

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Sienfeld and Pandis from from Kiehl,
and Rodhe
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Aromatics
Globally, about 25 Tg/yr of toluene and benzene
and are emitted with fossil fuels contributing
80, and biomass burning another 20 (Ehhalt,
1999) A reasonable total aromatic emission rate
might be 3 times the toluenebenzene emission
rate.

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Aromatics
Volatile aromatic compounds comprise up to 45 in
urban of the VOCs US and European locations. At
rural sites it is 1-2 Toluene, m-and p-xylenes,
benzene, 1,2,4-trimethyl benzene, o-xylene and
ethylbenzene make up 60-75 of this load

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Aromatics
Tunnel studies show that aromatic emissions
comprise 40-48 of the total nonmethane
hydrocarbon emissions for LD and HD vehicles
(Sagebiel, and Zielinska et al.) On a per mile
basis heavy duty trucks emit more than twice the
aromatic mass that light duty vehicles emit The
same aromatics as found in ambient air, comprise
60 of the LD aromatic emissions and 27 of the
HD

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Aerosols from Aromatics (Chamber studies)


1. Odum et al. 2. Izumi et al. 3. Holes, et al.
4. Kliendienst et al. 5. Forstner et al. 6.
Hurley et al 7. Jang and Kamens
m-xylene
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Particle phase reactions
In UNC chamber experiments partitioning Pankow
coefficients for aldehydes are much higher than
predicted partitioning coefficients, calculated
from the vapor pressures and activity
coefficients (Jang and Kamens, EST, 2001, Kamens
and Jaoui, EST, 2001 )
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Toluene gas phase reaction reactions
 
iKp i 760 RTx10-6 fom /Mw gi PoLi exp iKp
iCpart/iCgas xTSP
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Particle phase reactions
Ziemann and Tobias have reported the formation
of hemiacetals in the particle phase of secondary
organic aerosols
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• Aldehyde functional groups can react in the
  aerosol phase through heterogeneous reactions via
  hydration, polymerization, and hemiacetal/acetal
  formation with alcohols.
• Aldehyde reactions can be radically accelerated
  by acid catalysts such as particle sulfuric acid
  (Jang and Kamens, EST, 2001)

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Hemiacetal and acetal formation
OH
OH

-H
OH
H
H

ROH
R
H
O
H
OR
H
H
H
hemiacetal


-H
O
OR
OH
H
OH
2
2
H
H
H
OR
H
H
H
OR
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Why dont we see these large highly oxygenated
compounds?? Reverse reactions to the original
aldehyde parent structures can occur during
sample work up/solvent extraction procedures
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500 liter Teflon bag (Myoseon Jang, UNC)
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• To demonstrate the acid catalyzed aldehyde
  reaction, octanal was reacted directly on a ZnSe
  FTIR window by adding small amounts of aqueous
  H2SO4 acid catalyst solution (0.005 M). The
  spectra of the octanal/acid-catalyst system
  changed progressively as a function of time
• The aldehydic C-H stretching at 2715 cm-1
  immediately disappeared, the CO stretching band
  at 1726 cm-1 gradually decreased
• and the OH stretching at 3100-3600 cm-1 increased
  as hydrates formed.

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Future research areas.  

• Determine the importance of particle phase
  reactions as a source of SOA.
• Determine the importance of sesquiterpenes in SOA
  formation.
• Clarification of the impact of drought and
  relative humidity on biogenic emissions is needed
  so these factors can be incorporated into
  emission models.

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Future research areas (cont.)  

• Integrated chemical mechanisms for predicting SOA
  from biogenics and aromatic precursors.
• New analytical techniques to detect and quantify
  particle phase reactions. These need to be
  non-invasive or chemically soft so that complex
  particle phase reactions products are not
  decomposed.