oxidation products of terpenes: synthesis of reference compounds and novel sampling technique...
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Oxidation products of terpenes: synthesis of reference
compounds and novel sampling technique
Jevgeni ParshintsevJoonas Nurmi, Kari Hartonen and Marja-Liisa
Riekkola
University of Helsinki
Finland
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Background
• Aerosols are relatively stable suspension of solid or liquid particle in a gas, diameter ~0.002µm – 100 µm
• Either directly emitted into the atmosphere or formed there by chemical reactions (primary and secondary aerosols)
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Impact on the energy balance of the planet
direct indirect
-scattering &-absorption of solar radiation In the atmosphere
alter the: -formation-precipitation efficiency &-optical properties of clouds
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Aerosols are cooling the Earth’s surface immediately below them
• Directly:
lbexteI
I 0
Where I and I0 are the incident and transmitted light intensities respectively,L is the pathlength of the light beam, and bext is the extinction coefficient, (length)-1
pgext bbb spapsgagext bbbbb
Light extinctions due to gaseous and particulate absorption and scattering
BUT: light absorption by NO2(one,which contribute significantly) is usually much Less than the total light scattering and absorption by particles
Scattering is significant if D≈λ
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-and indirectly:Aerosol particles are “seeds” to start the formation of cloud droplets.
Aerosol concentration increase => the water gets spread over many more particles => smaller drops
Clouds with smaller drop:
-reflect more sunlight
-such clouds last longer
Both effects increase the amount of sunlight that is reflected to space without reaching the surface.
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It is thought that aerosol cooling may partially offset expected
global warming that is attributed to increases in the amount of carbon dioxide from human
activity…
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Atmospheric aerosols
http://www.ems.psu.edu/~lno/Meteo437/Aerosol.jpg, 31.7.06
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Why sesquiterpenes?
• ~9% of all non-methan VOCs in aerosols• almost unknown (compare to monoterpenes)• Have much higher aerosol potential than
monoterpenes. Example:• 2% of total biogenic VOC- emission is assumed
to be β-caryophyllene in Scandinavian atmosphere, the contribution by caryophyllene to the total biogenic secondary aerosol formation was estimated to be 12%!
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C15H24
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Analysis of sesquiterpenes oxidation products
• Usually collected on impactor plate or filter
• Extracted by proper solvent
• Analyzed by GC-MS (derivatization is needed if too polar)
• Identification & quantitation are almost impossible nowadays because of:
• Leak of reference materials, small amounts & great variety
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Conventional collection techniques
• Impactor, filter (usually quartz)
http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/tayu/ACT03E/img/09IMG/09_01.jpghttp://www.menlh.go.id/apec_vc/osaka/eastjava/hap_en/filter/5-3.gif 18.11.07
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Synthesis, isolation
• Solution of β-caryophyllene (~1000ppm) in dichloromethane was ozonolyzed by bubbling the ozone (produced by corona discharge) through the mixture
• Reaction was stopped when potassium iodide solution trap turned yellow (unreacted ozone, reaction time appr. 2h) O3 2KI H2O I2 2KOH O2
• 100 mg of Zn-powder and 10 ml of acetic acid/water mixture was added and refluxed for 1h
• Compounds were extracted by LLE to the dichloromethane
• Products were isolated and purified by flash-chromatography
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Scheme of oxidation of β-caryophyllene
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Paineistettu pylväskromatografialaitteisto
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Identification
• Mass-spectrometry with ESI- and EI-ionization and nuclear magnetic resonance spectroscopy were applied
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59
10
11CH312
3
21
O
CH24
CH38
CH37
O
H6
H6
48
9
10CH311
3
O
CH37
CH36
2
O
1
OH5
H5
Picture 1. Structures of β-nocaryophyllone aldehyde (left) and β-caryophyllene aldehyde (right) confirmed by NMR.
Structures
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Analysis of aerosol samples
• Self made standards were used in the analysis of ambient aerosol samples collected in Hyytiälä in 2003
• GC-MS and GC*GC-FID were used
• β-nocaryophyllone aldehyde was positively identified in one sample with amount of 17ng/m3
Parshintsev et al. accepted to Analytical and Bioanalytical Chemistry
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Conclusions I
• Two β-caryophyllene oxidation products were synthesized, isolated and analyzed for the precise structures for the first time
• Standards were used in analysis of ambient aerosol samples
• Presence of studied compounds in the samples proves their participation in biogenic aerosol formation
• However, more oxidation products of terpenes should be synthesized, to make their analysis possible, in order to understand the contribution of sesquiterpenes oxidation products to the biogenic aerosol chemistry
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Part II. Working principles of PILS
• particle growth in a mixing condensation particle counter
• droplet collection by a single jet inertial impactor
• used off-line, but continuous sample flow can provide on-line applications through SPE to HPLC or directly to API-MS
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PILS
Weber et al. Aerosol Science and Technology 35: 718–727 (2001)
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PILS
• Sample air flow 16.7 L/min (can be increased)
• Transport flow can be changed to relatively unpolar solvent
• Size separation before PILS, such as virtual impactor
• Gases removed by KOH, H3PO4, XAD-denuders
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Disadvantages
• Needs to be cleaned frequently (can be automated by running methanol/water steam through the system)
• 10% of gases passes through the denuders => “zero” samples should be run often
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Aerosol sampling
• Samples were collected during spring and summer 2007 in Hyytiälä (SMEARII-station), Finland
• Filter sampling was used as reference
• Samples were analyzed off-line: LLE to dichloromethane, concentration, GC-MS
Parshintsev et al. (2007) Manuscript in preparation
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Preliminary results
• Pinonaldehyde was found in all samples in great amounts
• Correlation with even/non-event was noticed due to the better time resolution
• Quantitation of other compounds is in progress
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Comparison with filter sampling
• Two hours filter samples showed amounts under LOD
• Only day or night samples contained amounts exceeding LOD
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Event week (except 103)
0,00
10,00
20,00
30,00
40,00
50,00
60,00
70,00
102,00 103,00 104,00 105,00 106,00 107,00 108,00 109,00
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Non-event week
0,00
10,00
20,00
30,00
40,00
50,00
60,00
70,00
113,00 114,00 115,00 116,00 117,00 118,00 119,00
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Conclusions II
• Time resolution of PILS is better than of filter sampling
• Less artifacts
• On-line possibility
• Transport flow can be 2-propanol (improves the collection efficiency for less polar compounds)
• However, optimization is still needed