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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@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 potential2. atmospheric emissions3. 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
myrcene
-pinene
-pinene d-limonene
Synthesis of TerpenesFrom 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 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
Yu et al. Hannel et al
-pinene 22-119 36-148
-pinene 16-119 7- 28**
limonene 13- 63 0- 21
3-carene 2- 21 8- 48
camphene 2- 21 5- 35
sabinene 0- 43
isoprene 0-228
Ambient Concentrations of selected terpenes (pptV)
Aerosol concentrations of selected terpenes products (ng m-
3) 1ng m-3 =~0.1pptVYu et al. Kavouras et al, 1998
Pinic acid 0.5 0.4- 85pinonic acid 0.8 9 - 141norpinonic acid 0.1- 38Pinonaldehyde 1.0 0.2- 32hydroxy-pinonaldehydes 0.5 oxo-liminoic acid 0.8Nopinone 133 0.0 - 13
Scheme 3
+
OO.
O
-pinene
O3
O O
OOO.
O
O
O
norpinonic acid
Criegee1
O
OH
O
O
hydroxypinonaldehyde
OO
norpinonaldehyde
o
+ HO 2+OH+CO
+ HCHO + CH 3OH
Criegee2
OH
O
pinonic acid
O
HO-CH 2
hydroxypinonaldehyde
OO
HO-CH 2
hydroxypinonic acid
OH
OH
O
hydroxypinonic acid
O
OH
OH
O
pinic acid
OOH
O
OH
O
OH
norpinic acid
O
pinalic acid
OOHO
O
O=CH
oxo-pinonaldehyde
+ HO 2+OH+CO
+ HCHO
CH2OH
.
.
pinonaldehyde
OO
Mechanisms can often explain the formation of products
Sesquiterpenes (C15H24)
terpenes15%
isoprene53%
SQS19%
others4%
alcohols9%
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
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
-Caryphyllene 53 min 2 min 2 min
-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)
with
w/o
Caryophylene
Limonene
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 2-methyl-6-methylene-1-7-octadien-3-one*
Aromatics p-cymene
linalool pinacarvone* alkenes
acetates verbenone* 1-decene
bornylacetate ethers 1-dodecene
butylacetate* 1-,8 cinole 1-hexadecene*
cis-3-hexenylacetate p-dimethylhydroxy benzene
p-mentha-1,2,8-triene*
aldehydes esters 1-pentadecene*
n-hexanal methylsalicyclate* 1-tetradecene
trans-2-hexenal
1. Temperature
2. light
3. injury
Factors that influence emissions
-pinene emission rates per gram of dry biomass as a function of temperature (Fuentes, et al. 2000)
E = Es exp { (T-Ts)} Tingy et al.
-pinene emissions compared to temp, and CO2 exchange (Mediterranean
Oak, Kesselmeire et al )
temp
CO2 exchange
-pinene
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 -caryophyllene and trans--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, 2-hexenal, and hexanol (Ebel et al. 1995)
Shade,et al (G. Res. Let.,1999) measured increases in monoterpene emissions of -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
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
Tropical forest 22Grass/shrubs/hot 22savanna 13Tropical rain forest 11Conifers and evergreens
20
Deciduous 7Re-growing woods 7Marsh/swamp/bogs 2Crops/woods-warm 3tundra 0.4desert 1
Global terpene sources (Tg/y)
Aerosol formation from Terpenes
-pinene
Aerosol potential (Odum theory)
Y MK
K MM
K
K Mo
om
om oo
om
om o
1 1
1
2 2
21 1,
,
,
,( ) ( )
0.95 ppm -pinene + 0. 44ppm NOx
O3
NO
NO2
NO2
model
data
Measured particle mass vs. model
reacted -pinene
data
model
particle phase pinonaldehye
model
data
OO
-pinene
Aerosol potential (Odum theory)
Y MK
K MM
K
K Mo
om
om oo
om
om o
1 1
1
2 2
21 1,
,
,
,( ) ( )
1 2 Kom,1 Kom,2 %Yield (Y)
3-carene 0.057 .0476 0.063 0.0042 2 -11
caryophyllene 1.00 N/A 0.0416 N/A 17-64
-humulene 1.00 N/A 0.0501 N/A 20-67
limonene 0.0239 0.363 0.055 0.0053 6 -23
-pinene 0.038 0.326 0.171 0.0040 2- 8
-pinene 0.113 0.239 0/094 0.0051 4-13
Griffin et al. biogenic aerosol yields
Relative aerosol potential of terpenoids
Andersson-Sköld and Simpson, JGR, 2001
Used a global photochemcial model to estimate the amount of terpenes and other biogenics that are reacted, ROGi.
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
Natural emissions Tg /y anthropogenic Tg /yr
Soil/mineral aerosol
©
1500Industrial
dust ©100
Sea salt © 1300 Soot 10
Volcanic dust © 30 Sulfate from SO2
190
biological debris
©50 Biomass
burning
90
Sulfates from biological gases
130 Nitrates from NOx
50
Volcanic Sulfates 20 VOCs 10
Nitrates 60
Biogenic aerosols 13-24
Total 3100 Total 450
Sienfeld and Pandis from from Kiehl, and Rodhe
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)
m-xylene
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
CH3
OH OH
CH2.
O=CH
NO NO2
+O2
CH3
H
OH
H .
CH3OH
*
O2
+ HO2
+ H2O
CH3
H
OH
H
CH3
O
O
+
.
CH3
O
CH3
H
OH
H
.O
NO
NO2
+O2
toluene
o-cresolbenzaldehyde
rearrangementOH
H
O .
H
H
O
H
OH
H
O
H
+ HO2
+O2
CH3H
+
methylglyoxalbutenedial
oxygen bridgeradical
+ HO2
?ring cleavageradical
CHO CHO
OH
CHO
OH
O2N
CH3
O
O
OH
O
CH3
O
O
O
CH3
O
O
O
H
OO
H3C
H
O O
CH3
O
H
O
O
H
CH3
O
O
H
H
O
O
H
H
O
O
O
H
CH3
O
O
H
H
O
O
O
CH3
CH3
O
H
O
H
O
O
HO
O
H3C
OH
OHO
CH3
O
O
HO
H
O
O
OH
H
O
O
OCH3
O
OH
OOH
CH3
O
O
O
CH3
O
OH
OO
OH
OO
OH
CH3OH O
O
H
O
OH
CH3
O
OHO
H
O
H
OHO
CH3
O
H
OH
CH3 H
O
OH
O
H H
O
OH
O
H
CH3
O
O
H
OOH CH3
O
H
O
OH
OOO
OH
CH3H O
O
Aromatic aldehydes
Ring-retaining carbonyls
Ring-opening carbonyls
Ring-opening oxo-carboxylic acids
Ring-opeining hydoxy-carbonyls
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 )
HO
CH3
NO2
HOH
OO
H
H
OOH
O
CH3 H
OOH
O
O
H
O
H
OH
CH3
O
O
O
Predlog 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
Toluene gas phase reaction reactions
iKp i= 760 RTx10-6 fom /{Mw i PoLi}
exp iKp = [iCpart]/[iCgas xTSP]
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;
nebulizer
(NH4)2SO4
Solution
aldehydesalcoholsglyoxal
aldehydesalcoholsglyoxal
(NH4)2SO4+H2SO4
Solution
500 liter Teflon bag (Myoseon Jang, UNC)
7.01
3.58
0.00
1.70
0.89
-0.020.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
reaction systems
yie
lds
(%
)
acid seed +decanol+ octanal
non-acid seed+ decanol+ octanal
• 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.
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