Authors M. T. Johnson, P. S. Liss, T.G. Bell and C.Hughes and J. Woeltjen
Paper given at the 6th International Symposium on Gas Transfer at Water Surfaces, Kyoto, Japan, May 2010.
Matatag-Curriculum and the 21st Century Skills Presentation.pptx
Transfer velocities for a suite of trace gases of emerging biogeochemical importance: Liss and Slater (1974) revisited
1. Transfer velocities for a suite of trace gases of emerging biogeochemical importance: Liss and Slater (1974) revisited M. T. Johnson 1 , P. S. Liss 1 , T.G. Bell 1 and C.Hughes 1 and J. Woeltjen 1,2 1 Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK 2 Now at: Helmholtz Centre for Environmental Research GmbH - UFZ, Permoser Strae 15, 04318 Leipzig, Germany. E-mail: martin.johnson@uea.ac.uk
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4. Notwithstanding the need to choose the 'best' transfer velocity parameterisations; solubility and diffusivity of the gas, and viscosity of the medium must be quantified for the gas of interest
14. Diffusivities of gases in air and water and viscosities of air and water calculated from best available paramterisations
15. Transfer velocities: various parameterisations of k l and k g implemented. Nightingale et al 2000 (k l ) and Jeffrey et al 2010 (k g ) used here.
16. Key assumptions: neutral bouyancy, all the assumptions made by the k l and k g parameterisations selected(!)
17. log(r g /r l ) for a suite of trace gases Log (r g /r l ) = 0 -> r g = r l -> 50% contribution to total transfer from both phases Log (r g /r l ) = 1 -> r g /r l = 10 -> 10% of total resistance due to liquid phase Log (r g /r l ) = -1 -> r g /r l = 0.1 -> 10% contribution to resistance from gas phase Log (r g /r l ) = 2 -> 1% contribution to transfer from liquid phase Log (r g /r l ) = -3 -> 0.1% contribution to transfer from gas phase
18. K H dependence of r g /r l For gases with solubility between 0.1 and 1000 mol/L/atm, both phases need to be considered in quantifying total transfer veloctiy
19. H2S CH3Cl C6H5CH3 CH3Br C2H5I CH3I HI CHCl3 CHI3 CH2CL2 DMS DES 2Butylnitrate Br2 2Propylnitrate CH2ICl BrCl DMDS 1Propylnitrate 1Butylnitrate HBr CH2Br2 SO2 Ethylnitrate CH2IBr CHBr3 Methylnitrate CH2I2 PPN I2 methylmethanoate PAN TEA methylethanoate TMA HCN propanal ethanal butanone HCl NHCl2 acetone OH DEA DMA nitromethane HNO2 MEA CH3CN NH3 2Nitrophenol HOBr NH2Cl MMA ICl MeOH EtOH IBr methylperoxide ethylperoxide IO HOI Phenol methanal HO2 K H dependence of r g /r l
21. Chemical enhancement of k l (and k g ?): Hoover and Berkshire 1969 α = τ / {(τ-1) + (tanh(x)/x)} where x = z(k hyd .τ/D) 1/2 z = layer thickness (inversely related to wind speed) D = molecular diffusivity of gas in medium k hyd = rate of (hydration) reaction of gas in seawater τ = 1+ ([unreacted gas]/[reacted products]) Tanh(x)/x When k hyd slow, x is small, tanh(x)/x=1, α = 1 When k hyd v fast, x is large, tanh(x)/x=0, α max = τ / (τ-1) = e.g. 1+ [XH 2 O] /[X] Hoover and Berkshire assume stagnant film model, which probably underestimates potential chemical enhancement for reversible reactions Assumptions: 1. Stagnant film model applies 2. reaction can be represented by pseudo-first-order rate constant – i.e. rate is proportional to concentration of gas of interest and independent of all other factors
22. Gases other than CO 2 and SO 2 , reactions other than hydration Reversible reactions i) undersaturation ii) supersaturation
23. Gases other than CO 2 and SO 2 , reactions other than hydration Irreversible reactions (e.g. photolysis) i) understaturation 2) supersaturation For an irreversible reaction that produces the gas of interest in the surface layer, a flux out would be enhanced and a flux in would be inhibited... The physics is the same in the gas phase, so the Hoover and Berkshire equation will apply there too...
24. Effect of chemical enhancement / inhibition on K for gases of different solubilities
25. Rate constants to give α = 2 in both gas and liquid phases (90 gases plotted)
35. Total transfer velocity K H k g k l u 10 T S K H 0 - Δ soln H/R Sc g Sc l D g D l ν g ν l η g T η l T,S Sensitivity analysis ρ g T ρ l T,S V b C D k g k l Estimated parameter /% uncertainty Highly soluble gas e.g. NH 3 Sparingly soluble gas. e.g CO 2 25 25 10 25 5 5 10 10 25 10 10 10 10 0.1 25 10 16 -0.04 4 0.05 -0.05 -1 10 1 -1 9 20 2 1 2 -0.2 2 4 4 -6 20 0.1 -0.1 1 Sparingly soluble gas. e.g CO 2 Highly soluble gas e.g. NH 3 Estimated parameter /% uncertainty D l D g 25 25 0.1 3 11 0.3 Table presents percentage change in total transfer velocity over range of parameter uncertainty