Symposium for the 30 th Anniversary of the Montreal Protocol. The Impact of Laboratory Photochemistry on the Montreal Protocol. James B.

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1 Symposium for the 30 th Anniversary of the Montreal Protocol The Impact of Laboratory Photochemistry on the Montreal Protocol James B. Burkholder Earth System Research Laboratory Chemical Sciences Division National Oceanic and Atmospheric Administration (NOAA) Boulder, CO USA

2 What is Laboratory Photochemistry? The study of elementary chemical processes under controlled conditions (relevant to the atmosphere) Reaction Rate Constants (OH, O( 1 D), Cl, ) UV Photolysis Rates Reaction Mechanisms Infrared Spectra How is it Relevant to the Montreal Protocol? Annex A, B, C, and F Compounds CFCs, Halons, HCFCs, HBFCs, and HFCs Replacement Compounds: HFOs The three-legged stool Building Blocks Honest Brokers of Information Burkholder et al. The Essential Role for Laboratory Studies in Atmospheric Chemistry Environ. Sci. & Tech., 2017, 51, Laboratory Studies à Modeling à Improved Understanding à Informed Policy

3 Atmospheric Lifetime Radiative Efficiency (RE) Metric Lifetime (t)! =! +! + " " %& " %( ) *+ Policy Relevant Metrics! ",- + Ozone Depletion Potential (ODP) Global Warming Potential (GWP) Laboratory Measurement Reaction Rate Coefficients (T, P) OH radical, O( 1 D), Cl-atom k (cm 3 molecule -1 s -1 ) T (K) OH + HCFC-141b Ozone Depletion Potential (ODP) ODP 1 = n 34 3 GWP T = f 1 f 3738!! M 3738!! M : τ 1 τ 3738!! Global Warming Potential (GWP) RE(τ) τ 1 ex p( T τ ) M : Int RF 3KL (T+ UV Absorption Spectrum (l,t) Infrared Absorption Spectrum Cross Section (10-18 cm 2 ) Cross Section (10-18 cm 2 ) /T (K -1 ) CFC Wavelength (nm) HCFC-225ca Wavenumber (cm -1 ) CFCs, Halons, HCFCs, HBFCs, and HFCs (Annex A,B,C, and F) Replacement Compounds: HFOs

4 Why Study Individual Compounds in the Laboratory? Composition and structure of a molecule influences its reactivity and photolysis (lifetime) OH Reaction Rate Coefficients Mixing Lifetime k (cm 3 molecule -1 s -1 ) OH + HFCs Days 6 Months Years 50 Years 500 Years Burkholder et al., Chem. Rev., 2015 Atmospheric degradation of ozone depleting substances, their substitutes, and related species

5 ClO Dimer Data Evaluation Proposed Replacements HCFC GWPs

6 ClO Dimer (Cl 2 O 2 ) Catalytic Ozone Destruction Cycle Molina and Molina (1987) Cl + O 3 ClO + O 2 ClO + ClO + M Cl 2 O 2 + M Cl 2 O 2 + hv Cl + ClOO ClOO Cl + O 2 Cl 2 O 2 photolysis rate is the key step for ozone depletion J = Nσ λ, T φ λ F λ, Z, SZA dλ Net: 2O 3 + hv 3O 2 Pre-2007 Studies and NASA (2006) Recommendation Pope et al. (2007) and NASA (2006) Recommendation Post 2007 Studies and NASA (2015) Recommendation Lab studies confirm importance of ClO dimer cycle Pope et al. challenges understanding of polar ozone depletion chemistry Labs responded, improve dataset, resolve discrepancy

7 ClO Dimer Data Evaluation Proposed Replacements HCFC GWPs

8 Data Evaluation Data evaluations play an important role in atmospheric chemistry research; since the 1970s. Recommendations of photochemical parameters for use in atmospheric models and laboratory studies NASA Data Evaluation includes: 8 CFCs 17 HCFCs 13 Halons 28 HFCs 16 HFOs Annex A: All Compounds Annex B: CF 3 Cl, CCl 4, and CH 3 CCl 3 (34) Annex C, Group I: 8 ** and 9 others (274) Group II: CHF 2 Br and CF 3 CHFBr (274) Group III: CH 2 BrCl (1) Annex F: All Compounds

9 Data Evaluation Recommendation Laboratory Studies 1.10 FOx Reactions Table 1E: FOx Reactions Reaction Temperature Range of Exp. Data (K) a A Factor E/R k(298 K) b f(298 K) c g Note O + FO F + O E 1 O + FO2 FO + O E 2 OH + CH3F CH2F + H2O (HFC 41) OH + CH2F2 CHF2 + H2O (HFC-32) OH + CHF3 CF3 + H2O (HFC-23) OH + CH3CH2F products (HFC-161) OH + CH3CHF2 products (HFC-152a) OH + CH2FCH2F CHFCH2F + H2O (HFC-152) OH + CH3CF3 CH2CF3 + H2O (HFC-143a) OH + CH2FCHF2 products (HFC-143) OH + CH2FCF3 CHFCF3 + H2O (HFC-134a) OH + CHF2CHF2 CF2CHF2 + H2O (HFC-134) OH + CHF2CF3 CF2CF3 + H2O (HFC-125) OH + CH3CHFCH3 products (HFC-281ea) OH + CH3CH2CF3 products (HFC-263fb) OH + CH2FCF2CHF2 products (HFC-245ca) OH + CH3CF2CF3 products (HFC-245cb) OH + CHF2CHFCHF2 products (HFC-245ea) OH + CH2FCHFCF3 products (HFC-245eb) OH + CHF2CH2CF3 products (HFC-245fa) OH + CH2FCF2CF3 CHFCF2CF3 + H2O (HFC-236cb) OH + CHF2CHFCF3 products (HFC-236ea) OH + CF3CH2CF3 CF3CHCF3 + H2O (HFC 236fa) OH + CF3CHFCF3 CF3CFCF3 + H2O (HFC-227ea) E E E E E E E E E E E E E E E E E E E E E E24 Atmospheric Lifetime 13.4 years ± 14% Uncertainty in laboratory measurements contributes to overall metric uncertainty

10 ClO Dimer Data Evaluation Proposed Replacements HCFC GWPs

11 Proposed Replacements (E) R-316c, 1,2-C4Cl2F6 (E,Z) (Z) CFC NOAA Laboratory Studies * Negligible OH reactivity * k(o(1d) = 1.6 x cm3 s-1 Reactive yield = 0.88 ± 0.02 UV Absorption Spectra Isomers have different UV absorption spectra T (K) (E) Photolysis is primary loss process (Z) * 100% Photodissociation (@ 193 nm) * c-c4f6 Photolysis and reaction product Papadimitriou et al. J. Phys. Chem. A (2013) Removed in the Stratosphere 2-D model calculations (NASA/Goddard) Lifetime (years) ODP (E) (Z) Long-lived ODSs

12 (E) Proposed Replacements R-316c, 1,2-C4Cl2F6 (E,Z) (Z) CFC NOAA Laboratory Studies Infrared Spectra GWP100 (E) 4160 (Z) 5400 Potent Greenhouse Gases Removed from consideration Timely laboratory studies provide industry and policy relevant information Papadimitriou et al. J. Phys. Chem. A (2013)

13 ClO Dimer Data Evaluation Proposed Replacements HCFC GWPs

14 Kigali Amendment to the Montreal Protocol Annex C: Controlled Substances Group Substance Number of isomers Ozone-Depleting Potential* 100-Year Global Warming Potential*** GWPs for HCFCs Group I CHFCl2 HCFC-21** CHF2Cl HCFC-22** CH2FCl HCFC C2HFCl4 HCFC C2HF2Cl3 HCFC C2HF3Cl2 HCFC CHCl2CF3 HCFC-123** C2HF4Cl HCFC CHFClCF3 HCFC-124** C2H2FCl3 HCFC C2H2F2Cl2 HCFC C2H2F3Cl HCFC C2H3FCl2 HCFC CH3CFCl2 HCFC-141b** C2H3F2Cl HCFC CH3CF2Cl HCFC-142b** C2H4FCl HCFC C3HFCl6 HCFC C3HF2Cl5 HCFC C3HF3Cl4 HCFC C3HF4Cl3 HCFC C3HF5Cl2 HCFC CF3CF2CHCl2 HCFC-225ca** CF2ClCF2CHClF HCFC-225cb** C3HF6Cl HCFC C3H2FCl5 HCFC C3H2F2Cl4 HCFC C3H2F3Cl3 HCFC C3H2F4Cl2 HCFC C3H2F5Cl HCFC C3H3FCl4 HCFC C3H3F2Cl3 HCFC C3H3F3Cl2 HCFC C3H3F4Cl HCFC C3H4FCl3 HCFC C3H4F2Cl2 HCFC C3H4F3Cl HCFC C3H5FCl2 HCFC C3H5F2Cl HCFC C3H6FCl HCFC Controlled HCFCs Isomers are unique substances 8 HCFCs have GWPs derived from experimental laboratory measurements Atmospheric reactivity (lifetime) Infrared absorption spectrum (RE) NOAA Study Determine GWPs missing in Annex C Atmospheric Lifetimes Radiative Efficiences (RE) Global Warming Potentials (GWPs) Papanastasiou et al. (2017) (in prep)

15 NOAA Study Reliable methods needed to estimate t and GWP in the absence of experimental data Atmospheric Lifetime (t) 1 τ = τ K[ τ K( ) \) 1 τ ]^ OH radical reaction Predominant loss process for HCFCs OH reaction rate coefficient Structure Activity Relationship (SAR): DeMore (1996) Estimated uncertainty: 20-30% Lifetime relative to CH 3 CCl 3 τ [373 K[ = k 3[`334`(272 K) k defe (272 K) 3[`334` τ K[ O( 1 D) rate coefficient and lifetime Trends in reactivity: Baasandorj et al. (2013) (NOAA) Lifetimes: comparison with similar compounds, SPARC (2013) UV photolysis lifetime Estimate based on HCFC chlorine content and distribution Comparison with 2-D model lifetimes: SPARC (2013) SAR works well

16 Global Warming Potential (GWP) NOAA Study Reliable methods needed to estimate t and GWP in the absence of experimental data GWP T = RE(τ) τ 1 ex p( T τ ) M : Int RF 3KL (T+ Estimating Infrared Absorption Spectra and RE Theoretical methods used to calculate infrared absorption spectra DFT: B3LYP/6-31G(2df,p); hours CPU time per molecule Empirical method used to calculate RE Hodnebrog et al. (2013) HCFC- 225ca o Isomers have unique infrared absorption spectra Molecular geometry influences spectrum o Strongest bands due to C-F stretches (~ cm -1 ) Molecular geometry determines exact frequency o Experimental spectra typically limited to >500 cm -1 region Theoretical calculations enable evaluation of low-frequency region Good agreement between experimental and calculated spectra Reliable RE determination (± ~15%)

17 Annex C HCFCs Metrics available for only a few HCFCs GTP GWP RE ODP Lifetime

18 Annex C HCFCs GTP GWP * Isomeric dependence RE ODP 33 > >0.05 Large range in metric values! Lifetime years * H-atom content * Isomeric form

19 NOAA Study Molecular geometry (isomeric form) influences OH reactivity (lifetime), RE, and GWP Consider on a molecule-by-molecule basis HCFC-225 Isomers aa CHF 2 -CCl 2 -CF 3 ba CHClF-CClF-CF 3 bb CHF 2 -CClF-CClF 2 ca CHCl 2 -CF 2 -CF 3 cb CHClF-CF 2 -CClF 2 cc CHF 2 -CF 2 -CCl 2 F da CClF 2 -CHCl-CF 3 ea CClF 2 -CHF-CClF 2 eb CCl 2 F-CHF-CF 3 Atm. Lifetime (years) Lifetime cb ca GWP 100 GWP 100 cb ca years GWP Estimated Uncertainty (this work) ~50% (<1 year lifetime) ~35% (>2 year lifetime) Lifetime RE ~25% <30% (depends on lifetime adjustment) * Reliable GWP determinations * Protocol relevant GWPs * Comparable to uncertainty for known compounds Careful laboratory studies could reduce GWP uncertainty from input parameters to ~20% (>2 year lifetime)

20 Acknowledgments NOAA Colleagues M. Baasandorj A. Mellouki F. Bernard J. Orlando M. Davis V. Papadimitriou K. Feierabend D. Papanastasiou D. Fahey R. Portmann T. Gierczak B. Rajakumar M. Gilles A. Ravishankara M. Harwood A.-M. Schmoltner C. Howard S. Solomon E. Jimenez R. Talukdar A. Jubb G. Vaghjiani S. McKeen R. Warren R. Mauldin R. Yokelson M. McGillen and others! CFCs HCFCs HFCs NASA Data Panel (2015) Burkholder, Sander, Abbatt, Barker, Huie, Kolb, Kurylo, Orkin, Wilmouth, Wine and past panel members Others!!!

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