Photoxidation products of Photoxidation products of alpha-pinene: Role of alpha-pinene: Role of
terpenes in cloud nucleationterpenes in cloud nucleation
PASI WorkshopPASI Workshop
Caltech, PasadenaCaltech, Pasadena
Jan 16,2004Jan 16,2004
Why does it rain in the Why does it rain in the rainforest?rainforest?
•The importance of this project is The importance of this project is to generate thermodynamical to generate thermodynamical data (i.e: equilibrium constant data (i.e: equilibrium constant and enthropy change) to and enthropy change) to understand the role of understand the role of monoterpenes in cloud monoterpenes in cloud nucleation over conifer forests.nucleation over conifer forests.
OutlineOutline
• Background info.Background info.
• ResultsResults
• ConclusionsConclusions
• AcknowledgementsAcknowledgements
Background info.Background info.
• Terrestrial vegetation releases terpenes Terrestrial vegetation releases terpenes to the atmosphereto the atmosphere
• Monoterpenes are highly reactive and undergo Monoterpenes are highly reactive and undergo free-radical addition with Ofree-radical addition with O33
• Photo-oxidations of terpenes and isoprene yield Photo-oxidations of terpenes and isoprene yield products, which partially remain in the gas phaseproducts, which partially remain in the gas phase
• Some less volatile photo-oxidation products Some less volatile photo-oxidation products partition between the gas phase and particulate partition between the gas phase and particulate phases, accumulate in the condense phase and, phases, accumulate in the condense phase and, thus contribute to the ambient particulate mass.thus contribute to the ambient particulate mass.
More background info…….More background info…….
• Alpha and beta pinene Alpha and beta pinene are typical biogenic are typical biogenic terpenes produced terpenes produced over conifer forests.over conifer forests.
• Their photoxidation Their photoxidation products are thought products are thought to play an important to play an important role in nucleation of role in nucleation of water.water.
http://czech.ifas.ufl.edu/content/Hydrology/warm.html
Pinonic AcidPinonic Acid
• Pinonic acid is Pinonic acid is formed by formed by photoxidation of photoxidation of alpha-pinene in alpha-pinene in presence of ozonepresence of ozone
• DATADATA
Formula: CFormula: C1010HH1616OO33 Molecular Weight: Molecular Weight: 184.23 184.23
∆∆Gº=Gº Gº=Gº pinonicpinonic- (Gº - (Gº a-pinenea-pinene+Gº +Gº ozoneozone) )
Keq= eKeq= e-∆Gº/RT-∆Gº/RT
Pinic AcidPinic Acid
• Pinic acid is Pinic acid is formed by formed by photoxidation of photoxidation of alpha-pinene in alpha-pinene in presence of presence of ozoneozone
• DATADATAFormula: Formula: CC99HH1414OO44
C10H16 + 5/3O3 C9H14O4 + HCHO
∆∆Gº=Gº pinic- (Gº a-pinene+5/3Gº ozone)Gº=Gº pinic- (Gº a-pinene+5/3Gº ozone)
O3
CH3
CH3CH3
CH3
OHCH3
CH3
O
OOH
alpha pinenepinic acid
+ HCHO
Chemical Equilibrium Chemical Equilibrium Constants Kp(T)Constants Kp(T)
The quantum statistical mechanical definition of the equilibrium constant follows the standard definition
Kc (T) = qj /V)nj
Here the product of the partition functions, the qj's , goes over all chemical species, products and reactants, nj are the stoichiometric coefficients (positive for products, negative for
reactants), and V is the reaction vessel volume. The temperature dependent partition function is defined as
q (T) = qtrans qrot qvib qelec
q(T) = {(2MkT/h2)3/2 V } {(1/2 /)(T3/ABC)1/2} {e -j /2T/ (1- e -j /T) )}o e -De/RT
Frequency calculations utilizing HFBasis set: 6-31G*
Geometry Optimization utilizing Force FieldsUFF
Geometry Optimization utilizing DFT Becke 3:P86 Basis set: 6-311G**
Data treatmentData treatment
Method validationMethod validation
MoleculeMolecule S°gas,1 S°gas,1 atm atm theoreticatheoretical l
(cal/molK)(cal/molK)11
S°gas,1 atm S°gas,1 atm experimentaexperimentall
(cal/molK)(cal/molK)
Error%Error%
HH22OO 188.84188.84 188.85188.85 0.005%0.005%
COCO22 215.53215.53 213.79213.79 0.80%0.80%
1 NIST
ResultsResultsEquilibrium constant for Equilibrium constant for transtrans- and - and ciscis-pinonic acid and -pinonic acid and ciscis-pinic acid-pinic acid
ln Keq trans and cis pinonic acid and cis-pinic acid versus Temperature
0
100
200
300
400
500
600
700
800
200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
Temperature (K)
ln K
eq
trans-pinonic acid cis-pinonic acid pinic acid
∆ ∆S for S for transtrans- and - and ciscis-pinonic acid and -pinonic acid and ciscis-pinic acid-pinic acid
ResultsResults
∆S cis- and trans-pinonic acid and cis-pinic acid as a function of temperature
-150
-100
-50
0
50
100
200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
Temperature (K)
∆S
(kc
al/m
ol.
K)
trans-pinonic acid cis-pinonic acid pinic acid
ConclusionsConclusions
• Pinic acid is more abundant than any pinonic acid isomer Pinic acid is more abundant than any pinonic acid isomer due to its higher equilibrium constant, as reported by Jenkin due to its higher equilibrium constant, as reported by Jenkin (2000)(2000)
• CisCis-pinonic acid is more abundant than -pinonic acid is more abundant than transtrans-pinonic acid -pinonic acid because its equilibrium constant is higher. This data because its equilibrium constant is higher. This data coincides with a study made by O’Dowd (2002)coincides with a study made by O’Dowd (2002)
• The enthropy change of the photoxidation of alpha-pinene The enthropy change of the photoxidation of alpha-pinene to yield pinic and pinonic acid is negative due to the to yield pinic and pinonic acid is negative due to the reduction of number of free molecules (i.e: ozone). The reduction of number of free molecules (i.e: ozone). The process enthropy for the formation of the process enthropy for the formation of the cis-cis- product is product is higher due to steric hinderance. It’s lower for pinic acid higher due to steric hinderance. It’s lower for pinic acid because of the stoichiometry of the reaction.because of the stoichiometry of the reaction.
Future studiesFuture studies
• Calculate the thermodynamical data for Calculate the thermodynamical data for transtrans-pinic acid.-pinic acid.
• Calculate the thermodynamical data for Calculate the thermodynamical data for other subproducts of the photoxidation of other subproducts of the photoxidation of alpha-pinene and beta-pinene.alpha-pinene and beta-pinene.
• Study the role of the major subproducts in Study the role of the major subproducts in cloud nucleation.cloud nucleation.
ReferencesReferences
• O'Dowd, C.D., Aalto, P., Hameri, K., Kulmala, M. O'Dowd, C.D., Aalto, P., Hameri, K., Kulmala, M. and Hoffmann, T. 2002. Atmospheric particles and Hoffmann, T. 2002. Atmospheric particles
from organic vapours. from organic vapours. NatureNature 416416: 497-498: 497-498
• Jenkin, M.E., Shallcross, D.E. and Harvey, J.N. Jenkin, M.E., Shallcross, D.E. and Harvey, J.N. 2000. Development and application of a possible 2000. Development and application of a possible mechanism for the generation of cis-pinonic acid mechanism for the generation of cis-pinonic acid from the ozonolysis of alpha and beta-pinene. from the ozonolysis of alpha and beta-pinene. Atmospheric Environment Atmospheric Environment 3434: 2837-2848: 2837-2848
AcknowledgementsAcknowledgements
• We would like to thank:We would like to thank:
– Dr. Mario Blanco from CaltechDr. Mario Blanco from Caltech– Dr. Sergio Aragon from UCSFDr. Sergio Aragon from UCSF– NSFNSF
