The presentation discusses about oxidation of Isoprene, the most reactive organic compound. It is also the highest present non-methane organic compound in the atmosphere. Isoprene is produced by plants and is highly reactive in the atmosphere. The major destruction of this compound is by oxidation. The major oxidants, the products formed and their yields in the oxidation process is discussed in the presentation. The presentation is done as part of graduate coursework at University of Florida. The author studied master's in environmental engineering sciences during the making of the presentation.

1. Gasphase Oxidation Products
of Isoprene
Student Presentation
ENV6932: Advanced Atmospheric Chemistry
December 6, 2016
Project Link: https://goo.gl/tCxueW
kalaivanan murthy
A qualitative investigation of gas phase oxidation of Isoprene.

2. Objectives
• To identify products and their yields of gas-phase Isoprene oxidation
• In presence of NOx
• In absence of NOx
• To enumerate the significance of isoprene oxidation.
• To elucidate the challenges and uncertainties in current research.
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3. Isoprene | Oxidation
• Isoprene oxidation products:
• Methacrolein
• Methyl-vinyl ketone
• Formaldehyde
• Minor products: organic nitrates, hydroxylcarbonyls, nitratocarbonyls.
• Oxidants:
• [OH] 1.5 x 106 molecules cm-3 0.06 pptv[6] daylight
• [O3] 700,000 x 106 molecules cm-3 30 ppbv[6] all-time
• [NO3] 480 x 106 molecules cm-3 20 pptv[6] night
• It is more pronounced in summer or when photon flux (sunlight) is high.
• Scholar in this area: Roger Atkinson↗ Almost all the oxidation reaction
mechanism for isoprene is formulated by Dr. Atkinson. He is professor
emeritus at University of California, Riverside.
Isoprene
(2-methyl-1,3-buta-diene)
Why concern?
Because it produces
highly reactive compounds
HO2 and RO2
Methacrolein
(2-methyl-prop-2-enal)
Methyl vinyl ketone
(but-3-en-2-one)
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4. MACR and MVK
• Isoprene + OH: kOH = 2.54 x 10-11 exp(410 / T)[5] cm3 molecule-1 s-1 100E-12298K
• Isoprene + O3: kO3
= 7.86 x 10-15 exp(-1913 / T)[5] cm3 molecule-1 s-1 0.00001E-12298K
MACR MVK
From OH:
0.23[3]
From OH:
0.32[14]
From O3:
0.39[9]
From O3:
0.16[9]
From NO3:
0.02[15]
From NO3:
0.05[15]
Reactivity with:
OH : 0.33*kOH
[9]
O3 : 0.09*kO3
[9]
Reactivity with:
OH : 0.19*kOH
[9]
O3 : 0.36*kO3
[9]
Key Points:
• MVK/MACR = 3:2
• ISOP MACR MVK are less reactive to O3.
• But [O3] > [OH], O3 oxidation is significant.
• MACR is more reactive to OH (than MVK).
• MVK is more reactive to O3 (than MACR).
• OH reaction more sensitive to temperature.
• In absence of NOx, MVK/MACR = 0.8.
• MVK is considered a more stable product.
• MACR MVK oxidation by NO3 is negligible.
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5. NO3 | HO2
• Isoprene + NO3:
k = 0.66E-12298K
[15]
• NO3 oxidation.
• NO2 reacts with O3 to form nitrate radicals NO3·,
which oxidizes isoprene to form condensable SOA.
• Products formed:
• Nitrooxycarbonyl
• Hydroxynitrate
• Minor products include hydroxycarbonyl, MACR MVK
and HCHO.
• RO2 + HO2
k = 3.4 x 10-13 exp (800 / T) cm3 molecule s-1 5E-12298K
• RO2/HO2 reactions: Isoprene oxidation in
absence of NOx.
• C5 unsaturated dihydroxy compounds (diols). (Rupert
and Becker, 2000). This provides evidence for peroxy
radical reactions.
• Oxidation products of peroxy radicals: carboxylic acids
–COOH, organic nitrate –ONO2, alkoxy radical RO·,
produces products of low volatility, and hence
formation of SOA.[13]
0.60 yield
Diol OH–R–OH
Peroxy Radical Reactions [k] cm3 molecule-1 s-1 [15]
RO2 + HO2 → ROOH + O2 k = 22E-12 (22*10-12)
RO2 + NO → RO + NO2 k = 4E-12
[12]
RO2 + NO → RONO2 ..organic nitrate
RO2 + NO2 → ROONO2 k = 9E-12 ..peroxy nitrate
RO2 + RO2 → 2RO + O2 k = 0.1E-12
O2NO–R–C=O
O2NO–R–OH
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6. HCHO
• Formaldehyde is the significant end-product of Isoprene oxidation, particularly in [OH] and [O3]
pathways.
• [HCHO] yields: 0.60[14] (OH oxidation) 0.90[9] (O3 oxidation)
• HCHO is sensitive to satellite radiometric resolution. Hence it can be measured from satellite data.
• It was due to the above reason, [HCHO] is used as a tracer for isoprene. (This is similar to the use of
methyl chloroform [CH3CCl3] to estimate [OH] concentration.)
• It has high cross section, and hence has high photochemical activity.
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7. Summary
• The major products formed in oxidation of isoprene: methacrolein, methyl vinyl ketone, formaldehyde
and nitratocarbonyl.
• The major oxidants of isoprene are [OH] [O3] [NO3] in which [OH] dominates in daylight, and [NO3]
dominates in night.
• In presence of NOx, formation of methyl vinyl ketone is closely 1.3x molar methacrolein, and formation
of formaldehyde is 60% molar yield.
• In absence of NOx, alkyl peroxy radicals and hydroperoxy radical becomes dominant, and results in
formation of carboxylic acid.
• In scarce (very less) NOx, alkoxy radicals and nitrogen-dioxide becomes dominant, besides peroxy
radical reaction. In addition, organo nitrates are formed in significant amounts, and peroxy nitrates are
formed in negligible amounts.
• The alkoxy radicals oxidizes to produce carbonyls and hydroperoxides. The hydroxyalkyl radicals,
formed as intermediate, has potential to isomerize, then oxidize, and eventually to form dihydrofuran.
• The products carboxylic acids, organonitrates and furans are less volatile than their parent
compounds, and hence has high potential to form secondary organic aerosol (SOA).
• Indisputably, formaldehyde (HCHO) is a significant end-product of hydrocarbon oxidation, and is
significant for two reasons: higher product yield, higher photochemical activity.
Discretion: The above qualitative premises has a quantitative justification (measures of product yields)–for many but not all
compounds–in the referred journals. However, except for [OH] products and recently [O3], the values are not always consistent
across similar journal articles, particularly [NO3] and [RO2].
RO2·
alkyl peroxy
radical
HO2 ·
hydro peroxy
radical
RO ·
alkoxy radical
RCOOH
carboxylic acid
RONO2
organonitrate
ROONO2
peroxynitrate
>C=O
carbonyl
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8. Labyrinth (Challenges)
• Secondary generation reactions.
• Although oxidation of MACR MVK by [O3] and [NO3] is considered insignificant, the reaction pathways are yet uncertain.
• Photolysis of primary oxidation products.
• Recently, it was found that MACR MVK undergo photolysis, a hypothesis more likely to be true.
• Peroxy Radical reactions are less understood.
• In absence NOx, RO2-RO2 and RO2-HO2 are found significant but the mechanisms and yields of products are uncertain.
• Condensed mechanisms and ‘representative compounds’
• Acetaldehyde and propanal for carbonyl oxidation products disguises the true property of alkyl compounds.
• Weather and Meteorology factors
• Photochemical factors such as daylight, nighttime, and Meteorological factors such as nocturnal inversion, makes it
challenging to estimate the products in ambient atmosphere.
• Reactivity vs Ambient Concentration
• Reactivity has to compliment with required ambient concentration for a higher product yield. In other words, high
reactivity does not mean high yields, unless with adequate concentration of oxidant.
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9. References
[1] Tuazon, E. C., & Atkinson, R. (1990). A product study of the gas‐phase reaction of Isoprene with the OH radical in the
presence of NOx. International Journal of Chemical Kinetics, 22(12), 1221-1236.
[2] Chameides, W. L., Lindsay, R. W., Richardson, J., & Kiang, C. S. (1988). The role of biogenic hydrocarbons in urban
photochemical smog: Atlanta as a case study. Science(Washington), 241(4872), 1473-1475.
[3] Jenkin, M. E., Young, J. C., & Rickard, A. R. (2015). The MCM v3. 3.1 degradation scheme for isoprene. Atmos. Chem.
Phys, 15(20), 11433-11459.
[4] Guenther, C. C. (2006). Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and
Aerosols from Nature). Atmospheric Chemistry and Physics, 6.
[5] Karl, M., Brauers, T., Dorn, H. P., Holland, F., Komenda, M., Poppe, D., ... & Wahner, A. (2004). Kinetic Study of the
OH‐isoprene and O3‐isoprene reaction in the atmosphere simulation chamber, SAPHIR. Geophysical research letters, 31(5).
[6] Seinfeld, J. H., & Pandis, S. N. (2016). Atmospheric chemistry and physics: from air pollution to climate change. John Wiley &
Sons.
[7] Perring, A. E., Wisthaler, A., Graus, M., Wooldridge, P. J., Lockwood, A. L., Mielke, L. H., ... & Cohen, R. C. (2009). A product
study of the isoprene+ NO 3 reaction. Atmospheric Chemistry and Physics, 9(14), 4945-4956.
[8] Skov, H., Hjorth, J., Lohse, C., Jensen, N. R., & Restelli, G. (1992). Products and mechanisms of the reactions of the nitrate
radical (NO3) with isoprene, 1, 3-butadiene and 2, 3-dimethyl-1, 3-butadiene in air. Atmospheric Environment. Part A. General
Topics, 26(15), 2771-2783.
[9] Aschmann, S. M., & Atkinson, R. (1994). Formation yields of methyl vinyl ketone and methacrolein from the gas-phase
reaction of O3 with isoprene. Environmental science & technology, 28(8), 1539-1542..
[10] Barket, D. J., Grossenbacher, J. W., Hurst, J. M., Shepson, P. B., Olszyna, K., Thornberry, T., ... & Biesenthal, T. (2004). A
study of the NOx dependence of isoprene oxidation. Journal of Geophysical Research: Atmospheres, 109(D11).
Project Link: https://goo.gl/tCxueW 9

10. References (cntd.)
[11] Von Schneidemesser, E., Monks, P. S., & Plass-Duelmer, C. (2010). Global comparison of VOC and CO observations in
urban areas. Atmospheric Environment, 44(39), 5053-5064.
[12] Ruppert, L., & Becker, K. H. (2000). A product study of the OH radical-initiated oxidation of isoprene: Formation of C 5-
unsaturated diols. Atmospheric environment, 34(10), 1529-1542.
[13] Kroll, J. H., & Seinfeld, J. H. (2008). Chemistry of secondary organic aerosol: Formation and evolution of low-volatility
organics in the atmosphere. Atmospheric Environment, 42(16), 3593-3624.
[14] Sprengnether, M., Demerjian, K. L., Donahue, N. M., & Anderson, J. G. (2002). Product analysis of the OH oxidation of
isoprene and 1, 3‐butadiene in the presence of NO. Journal of Geophysical Research: Atmospheres, 107(D15).
[15] Kwan, A. J., Chan, A. W. H., Ng, N. L., Kjærgaard, H. G., Seinfeld, J. H., & Wennberg, P. O. (2012). Peroxy radical
chemistry and OH radical production during the NO3-initiated oxidation of isoprene. Atmospheric Chemistry and Physics, 12(16),
7499-7515.
[16] Paulson, S. E., & Seinfeld, J. H. (1992). Development and evaluation of a photooxidation mechanism for isoprene. Journal
of Geophysical Research: Atmospheres, 97(D18), 20703-20715.
Project Link: https://goo.gl/tCxueW 10

11. Credits
• Questions
• Please feel free to ask/post questions.
• Acknowledgement
• Thank you audiences for your patience.
• Thank you Prof. Dr. Jang for the impressive lectures.
Project Link: https://goo.gl/tCxueW 11

12. Gasphase Oxidation Products
of Isoprene
Student Presentation
ENV6932: Advanced Atmospheric Chemistry
December 6, 2016
Project Link: https://goo.gl/tCxueW
kalaivanan murthy
Thank You
THE END