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@unc.edu
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.
The relative importance of
precursors to secondary aerosol
formation will depend on:
1. overall aerosol potential
2. atmospheric emissions
3. presence of other initiating reactants (O3, OH,
NO3, sunlight, acid catalysts)
1. Terpenoid
2. Aromatic
3. Particle Phase Reactions
(aldehydes and
alcohols)
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
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.
Different Terpene structures
a-pinene
b-pinene
d-limonene
myrcene
Synthesis of Terpenes
From CO2
Ruzika, 1953
No mechanism for
isoprene storage
While terpenes can
stored in resin duct
Global VOC Emissions Rates Estimates:
Guenther et al, 1995 (Tg/y)
Isoprene Monoterpenes ORVOC Total VOC
Woods
Crops
Shrub
Ocean
Other
All
372
34
103
0
4
503
95
6
25
0
1
127
177
45
33
2.5
2
260
821
120
194
5
9
1150
Ambient Concentrations of selected
terpenes (pptV)
Yu et al.
a-pinene
22-119
Hannel
et al
36-148
b-pinene
16-119
7- 28**
limonene
13- 63
0- 21
D3-carene
2- 21
8- 48
camphene
2- 21
5- 35
sabinene
0- 43
isoprene
0-228
Aerosol concentrations of selected
terpenes products (ng m-3)
1ng m-3 =~0.1pptV
Yu et al.
Pinic acid
pinonic acid
norpinonic acid
Pinonaldehyde
hydroxypinonaldehydes
oxo-liminoic acid
Nopinone
0.5
0.8
Kavouras et al, 1998
1.0
0.4- 85
9 - 141
0.1- 38
0.2- 32
0.5
0.8
133
0.0 - 13
Mechanisms can
often explain the
formation of
products
Sesquiterpenes (C15H24)
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)
alcohols others
9%
4%
Flux data,
Atlanta
forest,
Helmig et
al., 1999
terpenes
15%
SQS
19%
isoprene
53%
Lifetimes of Sesquiterpenes
OH
NO3
O3
a-Cedrene
2.6 hours
4 min
14 hours
a-copaene
1.9 hours
2 min
2.5 hours
b-Caryphyllene
53 min
2 min
2 min
a-Humulene
36 min
1 min
2 min
Longifiolene
3.7 hours
49 min
23 days
average OH concentration =1.6x106; NO3 = 5x108 for 12
hours of night time; O3 = 7x1011 (molecules cm-3)
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
Other emissions (Winer et al. ,
Kesselmeier and Staudt )
alcohols
ketones
alkanes
p-cymen-8-ol*
2-heptanone
n-hexane and C10-C17
cis-3-hexen-1-ol
linalool
2-methyl-6-methylene1-7-octadien-3-one*
pinacarvone*
acetates
verbenone*
1-decene
bornylacetate
ethers
1-dodecene
butylacetate*
1-,8 cinole
1-hexadecene*
cis-3-hexenylacetate
aldehydes
p-dimethylhydroxy
benzene
esters
p-mentha-1,2,8triene*
1-pentadecene*
n-hexanal
methylsalicyclate*
1-tetradecene
trans-2-hexenal
Aromatics
p-cymene
alkenes
Factors that influence emissions
1. Temperature
2. light
3. injury
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.
a-pinene emissions compared to
temp, and CO2 exchange (Mediterranean
Oak, Kesselmeire et al )
a-pinene
temp
CO2 exchange
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 bcaryophyllene and trans-b-ocimene decreased
little (-6%) from the non-drought conditions.
Hansen and Seufert,(1999).
Emissions from drought-stressed apple leaves
seem to show significant increases in hexanal, 2hexenal, 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
Plant damage
Emissions from damaged leaves contain C6aldehydes 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.
Global terpene sources (Tg/y)
Tropical forest
Grass/shrubs/hot
savanna
Tropical rain forest
Conifers and evergreens
Deciduous
Re-growing woods
Marsh/swamp/bogs
Crops/woods-warm
tundra
desert
22
22
13
11
20
7
7
2
3
0.4
1
Aerosol formation from Terpenes
Aerosol potential (Odum theory)
Y  Mo
a 1 K om,1
(1  K om,1 M o )
 Mo
a 2 K om, 2
(1  K om, 2 M o )
a-pinene
gas phase reactions
min-1 or ppm-1 min-1
1a-pinene + O3  .4 Criegee1 + .6 Criegee2
1.492 exp-732/T
2. Criegee1  .3 pinacidgas + .15 stabcrieg1 + .8 OH
6
+ .5 HO2 + .3 pinaldgas + .25 oxy-pinaldgas + .3 CO
1x10
3. Criegee2  .35 crgprod2 + .5 oxy-pinaldgas
6
+.35 HCHO + .15 stabcrieg2 +.8 OH + .5 HO2
1x10
-3
4. stabcrieg1 + H2O  pinacidgas
6x10
10. oxy-prepinacid +HO2  oxy-pinacid
677 exp1040/T
-7
16. pinacidgas {walls} 
4x10 exp2445/T
partitioning reactions
22. stabcrieg1 + pinaldgas  seed1
25. pinacidgas + seed1  seed1 + pinacidpart
34. diacidgas + pinacidpart --> pinacidpart + diacidpart
35. diacidpart  diacidgas
44. diacidpart {walls} 
29.5,
29.8,
68,
14
3.73x10 exp-10285/T
0.0008,
0.95 ppm a-pinene + 0. 44ppm NOx
model
NO
data
O3
NO2
NO2
Measured particle mass vs. model
reacted a-pinene
data
model
particle phase pinonaldehye
O
O
data
model
Aerosol potential (Odum theory)
Y  Mo
a 1 K om,1
(1  K om,1 M o )
 Mo
a 2 K om, 2
(1  K om, 2 M o )
a-pinene
Griffin et al. biogenic aerosol yields
a1
a2
Kom,1
Kom,2
%Yield
(Y)
D3-carene
0.057
.0476
0.063
0.0042
2 -11
caryophyllene
1.00
N/A
0.0416
N/A
17-64
a-humulene
1.00
N/A
0.0501
N/A
20-67
limonene
0.0239
0.363
0.055
0.0053
6 -23
a-pinene
0.038
0.326
0.171
0.0040
2- 8
b-pinene
0.113
0.239
0/094
0.0051
4-13
Relative aerosol potential of terpenoids
AnderssonSköld and
Simpson, JGR,
2001
Griffin et al, JGR, 2000
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
Sienfeld and Pandis from from Kiehl, and
Rodhe
Natural emissions
Tg /y
Soil/mineral aerosol
©
Sea salt
©
1500
1300
Volcanic dust ©
30
biological debris
50
©
Sulfates from
biological gases
Volcanic Sulfates
Nitrates
Biogenic aerosols
Total
130
20
anthropogenic
Tg /yr
Industrial
dust ©
Soot
100
Sulfate from
SO2
Biomass
burning
Nitrates from
NOx
VOCs
190
Total
450
10
90
50
10
60
13-24
3100
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
toluene+benzene emission rate.
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
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
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
Aromatic aldehydes
CHO
CHO
CHO
OH
OH
O2 N
Ring-retaining carbonyls
CH 3
CH 3
CH 3
O
O
O
O O
O
O
O
O
O
H3 C
H
O
O
O
CH 3
H
OH
O
Ring-opening carbonyls
O
CH 3
O
O
H
O
O
H
H
O
H
H
O
O
O
H
O
CH 3
O
O
CH 3
O
H
O
CH 3 H
H
H
Ring-opening oxo-carboxylic acids
O
O
O
O
HO
O
H3 C
HO
HO
OH
OH
O
CH 3 O
O
O
O
O
OH
O
O
O
H
CH 3
O
O
O
CH 3
OH
H
CH 3
H
O
O
OH
OH
O
O
O
OH
OH
O
CH 3
Ring-opeining hydoxy-carbonyls
OH
O
CH 3
H
O OHO
CH 3
O
H
CH 3 H
O O
O
O
H
OH
OH
OH
H
H
O
CH 3
O
H
O
H
O
O
H
O
OH
O
H
OH
O
O
OH
OH
O
CH 3
O
O
CH 3
O
O
H
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, ES&T, 2001, Kamens and Jaoui, ES&T,
2001 )
Toluene gas phase reaction reactions
Pred
log iKp
Exp.
log iKp
4.25
-3.8
5.64
-5.69
5.41
-3.86
6.10
-2.66
5.56
-3.23
5.38
-3.91
CH 3
HO
NO 2
CH 3
O
O
O
O
O
HO
H
OH
O
O
H
H
OH
H
O
O
H
OH
O
O
CH3
H
iK = 760 RTx10-6 f
pi
om /{Mw
exp iKp = [iCpart]/[iCgas xTSP]
gi PoLi}
Particle phase reactions
Ziemann and Tobias have reported the
formation of hemiacetals in the particle
phase of secondary organic aerosols
• 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,
ES&T, 2001)
Why don’t we see these large
highly oxygenated compounds??
Reverse reactions to the original
aldehyde parent structures can occur
during sample work up/solvent
extraction procedures;
500 liter Teflon bag (Myoseon Jang, UNC)
nebulizer
(NH4)2SO4
Solution
aldehydes
alcohols
glyoxal
(NH4)2SO4+H2SO4
Solution
aldehydes
alcohols
glyoxal
2:
1-
de
ca
st
ep
no
3:
l(
A
oc
)
ta
na
l(
A
)
to
ta
l(
st
A
ep
)
2:
1de
ca
st
ep
no
3:
l(
N
oc
)
ta
na
l(
N
)
to
ta
l(
N
)
st
ep
2:
st
oc
ep
ta
3:
na
1l(
de
A
)
ca
no
l(
A
)
to
ta
l(
A
)
st
ep
2:
st
oc
ep
ta
3:
na
1l(
st
ep
yields (%)
7.00
7.01
6.00
0.00
acid seed +
decanol
+ octanal
5.00
4.00
3.58
3.00
-0.02
non-acid seed
+ decanol 3.03
+ octanal
2.00
1.70
1.00
2.39
1.80
0.89
0.00
reaction systems
• 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 C=O stretching
band at 1726 cm-1 gradually decreased
• and the OH stretching at 3100-3600 cm-1
increased as hydrates formed.
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.
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.