Studying Ozonolysis Reactions of 2-Butenes Using Cavity Ring-down Spectroscopy Liming Wang, Yingdi Liu, Mixtli Campos-Pineda, Chad Priest and Jingsong Zhang Jet Propulsion Laboratory, California Institute of Technology Department of Chemistry, University of California, Riverside

1 NO x O 3, PAN, HNO 3, … Particles VOCs: Alkanes, Alkenes, …

NO x O 3, PAN, HNO 3, … Particles VOCs: Alkanes, Alkenes, … ++ O 2 R, alkyl radical RH, hydrocarbon HONO +hv OH NO RO 2 HO 2 NO 2 ROONO 2 RONO 2 RO 2 carbonyl + alcohol ROOH NO 2 O3O3 O2O2 hv OH Alkenes OH production mechanism in alkene + O 3 reactions

Ozonolysis of Alkenes Reactions Important oxidation pathway of alkenes in troposphere – High concentrations of O 3 and alkenes in polluted areas Secondary organic aerosol (SOA) production in ozonolysis of large alkenes Production of OH radical (10-90% yield) and a source of HO x radical Production of Criegee intermediate (CI) CI react with many important molecules in the atmosphere : NO 2, SO 2, H 2 O etc OH production mechanism is not completely established Lack of kinetics information of CI

Mechanisms of trans-2-Butene + O 3 O 3 OH Primary Ozonide (TS) Criegee Intermediates syn anti Atkinson, Paulson, Donahue, Anderson, Marston, Cremer, and many others.. H 3 C C H O O Dioxirane CRDS Co-product of OH in the decomposition of Criegee intermediate

Our Focus By detecting co-product of OH using CRDS CH 2 CHO from (trans/cis)-CH 3 CH=CHCH 3 + O 3 OH production mechanism

Cavity Ring-Down Spectroscopy I in I out High-reflectivity Mirrors R  % lsls L B B Time profile Signal Processing Spectrum Time Intensity A Wavelength A Detector Measure Rate of intensity decay instead of Magnitude of attenuation

Advantages of CRDS Quantitative and absolute concentration measurements Insensitive to intensity fluctuation of pulsed laser Measuring intensity decay High sensitivity with a long effective absorption path (~ km) in a compact setup (~ m): 20  s ring-down time ~ 6 km Spectroscopic selectivity Real-time and in-situ detection A. O’Keefe and D.A.G. Deacon, Rev. Sci. Instrum. 59, 2544 (1988); J.J. Scherer et al, Chem. Rev. 97, 25 (1997); M. D. Wheeler et al. J. Chem. Soc. Faraday Trans. 94, 337 (1998).

Reference CRDS Spectrum of Vinoxy Radical Vinoxy radical was produced from photolysis of ethyl vinyl ether precursor. CC O H H H. L. Wang et al.

trans-2-Butene + O 3 [CH 2 CHO] ~3  molecule cm -3 HCHO

Yields of CH 2 CHO decrease with increased total pressure. Possible Reasons: Increased CH 2 CHO depletion by O 2 ; Pressure Dependence of CH 2 CHO Production trans-2-butene and O 3 in N 2 total pressure 8 Torr 9.5 Torr 12 Torr 15.5 Torr 19 Torr 37 Torr 65 Torr 11

Kinetics model No.ReactionBranching ratioRate const 1C4H8 + O3 = CH3CHOO + CH3CHO00 2C4H8 + O3 = OH + CH2CHO + CH3CHO;0.55.7E-17 3C4H8 + O3 = CH2CO + H2O + CH3CHO; E-18 4C4H8 + O3 = CH3OH + CO + CH3CHO; E-17 5C4H8 + O3 = CH4 + CO2 + CH3CHO; E-17 6C4H8 + O3 = CH3CHO + other products; E-17 7C4H8 + O3 = CH3CHO + OH + other products;00 8CH2CHO + O2 = (CHO)2 + OH E-15 9CH2CHO + O2 = HCHO + CO + OH E-14 10CH2CHO + O2 = others E-14 11OH + O3 = HO2 + O2 1.6E-12 12OH + C4H8 = others 6.4E CH3OH + ·OH → (·)CH2OH + H2O E CH3OH + ·OH → CH3O + H2O CH2OH + O2 = HCHO + HO2 9.1E-12 16HCHO + ·OH → HCO + H2O 1E-11 17OH + CH2CHO = other products; 1E-11 18CH3CHO + OH = CH2CHO + H2O E-13 19CH3CHO + OH = H2O + CH3CO CH2CHO = other products; 0 21CH2CHO = WALL; 10 22C4H8 + CH2CHO = other products; 0 23CH3CHOO + C4H8 = P; 1E-15 24CH3CHOO + O3 = P; 1E-13 25CH3CHOO + CH3CHO = SOZ; 1E-12 26CH3CHOO = OH + CH2CHO; 76 27CH3CHOO = WALL; 10 28CH3CHOO + HCHO = SOZ2; 1E-12 29CH3CHOO + CH2CHO = P; 1E-11 Rate constants units: first order: s -1 ; second order: cm 3 molecule -1 s -1 ; third order: cm 6 molecule -2 s -1

Kinetics model No.ReactionBranching ratioRate const 1C4H8 + O3 = CH3CHOO + CH3CHO00 2C4H8 + O3 = OH + CH2CHO + CH3CHO;0.55.7E-17 3C4H8 + O3 = CH2CO + H2O + CH3CHO; E-18 4C4H8 + O3 = CH3OH + CO + CH3CHO; E-17 5C4H8 + O3 = CH4 + CO2 + CH3CHO; E-17 6C4H8 + O3 = CH3CHO + other products; E-17 7C4H8 + O3 = CH3CHO + OH + other products;00 8CH2CHO + O2 = (CHO)2 + OH E-15 9CH2CHO + O2 = HCHO + CO + OH E-14 10CH2CHO + O2 = others E-14 11OH + O3 = HO2 + O2 1.6E-12 12OH + C4H8 = others 6.4E CH3OH + ·OH → (·)CH2OH + H2O E CH3OH + ·OH → CH3O + H2O CH2OH + O2 = HCHO + HO2 9.1E-12 16HCHO + ·OH → HCO + H2O 1E-11 17OH + CH2CHO = other products; 1E-11 18CH3CHO + OH = CH2CHO + H2O E-13 19CH3CHO + OH = H2O + CH3CO CH2CHO = other products; 0 21CH2CHO = WALL; 10 22C4H8 + CH2CHO = other products; 0 23CH3CHOO + C4H8 = P; 1E-15 24CH3CHOO + O3 = P; 1E-13 25CH3CHOO + CH3CHO = SOZ; 1E-12 26CH3CHOO = OH + CH2CHO; 76 27CH3CHOO = WALL; 10 28CH3CHOO + HCHO = SOZ2; 1E-12 29CH3CHOO + CH2CHO = P; 1E-11 Rate constants units: First order: s -1 ; Second order: cm 3 molecule -1 s -1 ; Third order: cm 6 molecule -2 s reactions

14 Pressure dependence study of simulation when a= 0.3 and a =0.5 and experimental results. CH 2 CHO yield (a) is

Summary CH 2 CHO is observed from 2-butene ozonolysis reactions: – CH 2 CHO + OH is a considerable channel; – Chemical kinetic modeling of the vinoxy and formaldehyde production indicates that the CH 2 CHO yield is and in the ozonolysis reaction of trans- and cis-2- butene, respectively. – The CH 2 CHO yields are consistent with the OH yields of trans- and cis-2-butene. CH 2 CHO is observed from 2-butene ozonolysis reactions: – CH 2 CHO + OH is a considerable channel; – Chemical kinetic modeling of the vinoxy and formaldehyde production indicates that the CH 2 CHO yield is and in the ozonolysis reaction of trans- and cis-2- butene, respectively. – The CH 2 CHO yields are consistent with the OH yields of trans- and cis-2-butene. 15

Acknowledgement National Science Foundation $$ Keck Foundation $$ Prof Jingsong ZhangProf Liming Wang Mixtli Campos-Pineda Chad Priest