Current Research in the Atmospheric Degradation of Isoprene Theodore S. Dibble Chemistry Department SUNY-Environmental Science and Forestry Syracuse, NY

OH O 2 OH O 2, NO O3O3 HOOH Global Organic compound emissions CH Tg/year Isoprene 500 Tg/year Other 650 Tg/year Isoprene in the Air (Oxidizes SO 2 to sulfuric acid) (Health Hazard) (“Vacuum cleaner of the atmosphere”)

Multiple Degradation Pathways! 60% 5% 5% 30% SAR ‘96 56% 2% 5% 37% CVTST ‘00 41% S. Paulson 59% ‘92

Multiple Degradation Pathways! Next: R + O 2  ROO 34% 22% 2% 5% 29% 8% R. Zhang and S. W. North CVTST ‘01

Structure-Reactivity Relationships Kcal/mole Favor decomposition of RO making RCHOH rather than R : leaving group effect. Paulson ‘92 and Dibble ‘99 (DFT) Endothermic production of vinyl radical unlikely ROO + NO  RO + NO 2

H-bonds and Barton (1,5 H-shift) k = A e -Ea/RT A = (ek B T/h) e  S  /R  S  = S(TS)-S(Reactant) usually negative  S  usually -3R; here  S  is -R  A is unusually large Dibble ‘02 (Z) V

Tunneling in the 1,5 H-shift Reaction coordinate Reactant Product Tunneling rate times the classical rate! Dibble ‘02

Chemically Activated Reactions RR’CHOO + NO Kcal/mole RR’CHO + NO 2 R + R’CH=O RR’CHO* quenching decomposition Prompt (chemically activated) decomposition / isomerization dominates fate of RO from isoprene in 1 atm of air. R. Zhang and S. W. North ‘03

Double H-Bond and Double H-shift 0 4 Kcal/ mole -19 Kcal/mole

Traditional Atmospheric Chemistry - large vessel, initiate chemistry. FTIR/GC/HPLC of products - OH fluorescence for OH + isoprene kinetics Newer Methods - Chemical Ionization-MS in flow tube for OH and O 2 kinetics - large vessel, Atmospheric Pressure Ionization MS, MS/MS for products -OH cycling for kinetics of alkoxy radical reactions Theory - Density Functional Theory, basis set additivity for ab initio - Canonical Variational Transition State Theory (CVTST) - Master Equation (thermal and activated processes) Methods

Conclusions-1 Isoprene from human breath (1,3-butadiene and isoprene from outside air) OH from O 3 + alkenes (including isoprene) NO brought indoors by ventilation (not necessary) All the chemistry reviewed here is occurring in this room right now.

Conclusions-2 Fundamental interest and atmospheric importance chemical activation source of O 3 tunneling sink for OH structure-reactivity source for HOOH H-bonds Great example for lecture and homework! Acknowledgements NSF-ATM Simon W. North

Atmospheric Chemistry of Organic Compounds OH + CH 4  HOH + CH 3 CH 3 + O 2  CH 3 OO Unpolluted Air (very low [NO]) 2 CH 3 OO  2CH 3 O + O 2 2[ CH 3 O + O 2  CH 2 =O + HOO ] 2 HOO  HOOH + O 2 Polluted Air (NO) CH 3 OO + NO  CH 3 O + NO 2 CH 3 O + O 2  CH 2 =O + HOO HOO + NO  OH + NO 2 2[ NO 2 + h  NO + O ] 2[ O + O 2  O 3 ] net : CH O 2  2 O 3 + HOH + CH 2 =O