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Interhemispheric gradient of hydroxyl (OH) in the troposphere

Revised from AGU Fall Meeting, 2013. R esearch I nstitute for G lobal C hange. Interhemispheric gradient of hydroxyl (OH) in the troposphere. P. K. Patra , T . Arnold, E. L. Atlas, M. C. Krol , B. R. Lintner , S. A. Montzka , B. B. Stephens, B . Xiang,

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Interhemispheric gradient of hydroxyl (OH) in the troposphere

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  1. Revised from AGU Fall Meeting, 2013 Research Institute for Global Change Interhemispheric gradient of hydroxyl (OH) in the troposphere P. K. Patra, T. Arnold, E. L. Atlas, M. C. Krol, B. R. Lintner, S. A. Montzka, B. B. Stephens, B. Xiang, J. W. Elkins, P. J. Fraser, A. Ghosh, E. J. Hintsa, D. F. Hurst, K. Ishijima, P. B. Krummel, B. R. Miller, K. Miyazaki, F. L. Moore, J. Mühle, S. O’Doherty, R. G. Prinn, L. P. Steele, M. Takigawa, H. J. Wang, R. F. Weiss, S. C. Wofsy, D. Young Presented at AGU Fall Meeting, San Francisco, December 2013

  2. Introduction • Hydroxyl radicals work as the cleansing agent of air pollutant, and majority of the greenhouse gases • OH has a very short lifetimes in the atmosphere, exhibiting large spatial and temporal variations • So far indirect methods using 14C and CH3CCl3 could only be applied for inferring global distribution of OH • There is a large disagreement between the NH/SH OH ratios simulated by chemistry-transport models and that derived from observations • We use wide-ranging measurements and improved chemistry-transport model are employed for estimating NH/SH OH ratio

  3. Methodology Bottom-up emission inventories JAMSTEC’s Chemistry-Transport Model Measurements from AGAGE, HIPPO, NOAA/ESRL

  4. Drivers of interhemispheric gradients Transport All highly variable in space and time Chemistry Emissions CH3CCl3 concentrations : an observable quantity

  5. Summary of HIPPO flights and CMAP rainfall, and surface network HIPPO data from central Pacific only NH: Northern Hemisphere SH: Southern Hemisphere

  6. “Control” emissions and loss of CH3CCl3 d(Burden)/dt = Emission – Burden/τtotal(WMO/SAOD-style) τinstananeous= Burden/Loss (IPCC/Prather-style) Analysis period Emission distribution up to 1998 (McCulloch and Midgley, 2001) Global totals optimized by TM5 (M. Krol), exponentially decreased after ~2000

  7. Temporal evolutions of CH3CCl3in the atmosphere(depends mainly on global total OH and emission)

  8. Temporal evolutions of inter-site CH3CCl3 difference(sensitivity to NH/SH OH ratio; model resolution; NH/SH emission ratio) ACTM_TC : NH/SH OH ratio = 0.99 ACTM_OH : NH/SH OH ratio = 1.26 (σpress=1.0-0.16) Emission dominating  Loss dominating 

  9. Temporal evolutions of inter-site CH3CCl3 difference(sensitivity to NOAA flask measurements sites) ACTM_0.99 ACTM_1.26

  10. Latitude-altitude variations of HIPPO & ACTM SF6 using EDGAR4.2(validation of NH to SH transport in ACTM)

  11. Vertical/Meridional gradients of CH3CCl3 (HIPPO1-5) ACTM_TC : NH/SH OH ratio = 0.99 ACTM_OH : NH/SH OH ratio = 1.26 (σpress=1.0-0.16)

  12. NH-SH CH3CCl3 sensitivity to NH/SH OH ratio Monthly mean Annual mean

  13. Estimation of NH/SH OH ratio: Annual/emission dependence Seasonal/chemistry dependence AGAGE: 0.98±0.13 NOAA : 0.97±0.11 HIPPO : 0.96±0.63

  14. Sensitivity of NH/SH OH ratio to emission distribution & totals Global total emissions at annual timescale ACTM_1.26 ACTM_0.99 NH/SH emission ratio: Under no circumstance, the ACTM_1.26 model can achieve the observed MHD-CGO CH3CCl3 difference This result precludes an NH/SH OH ratio of 1.26

  15. Sensitivity to emission/OH totals and distribution Model-observation mismatch for ACTM_1.26 remained higher than ACTM_0.99 Greater than Control global total emissions and OH worsen the seasonal cycle amplitude of NH-SH CH3CCl3 concentration gradient

  16. Comparison with previous studies *NH/SH OH ratio is 0.87 for ACTM_0.99 when the two hemispheres are divided following the monthly locations of the Inter-tropical Convergence Zone (ITCZ),

  17. Conclusions • ACTM can now simulate all major greenhouse gases and SF6 simulations have been used for validating meridional transport • We have estimated the NH/SH OH ratio to be very close to 1 (i.e., 0.97±0.12) using “multi-platform” observations and simulations of CH3CCl3 • Our result contradicts the NH/SH OH ratios obtained from the chemistry-climate models • The NH/SH OH ratio have large implications for forward and inverse modeling of greenhouse and air polluting species • CH4 emissions have to be increased by 8% from 398 Tg-CH4/yr in the NH and decreased by 25% from 151 Tg-CH4/yr in the SH for ACTM_1.26 compared to ACTM_0.99

  18. How well do we know global total OH?(tests using multiple tracers) Lifetimes (in yr) Emissions from EDGAR4.2

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