Lecture 7 Gases and Gas Exchange 华盛顿大学-海洋化学课件.ppt

Effect of El Nino on ?pCO2 fields High resolution pCO2 measurements in the Pacific since Eq. Pac-92 Eq Pac-92 process study Cosca et al. in press El Nino Index PCO2sw Always greater than atmospheric * Lecture 7 Gases and Gas Exchange Composition of the atmosphere Gas solubility Gas Exchange Fluxes Effect of wind Global CO2 fluxes by gas exchange Sarmiento and Gruber (2002) Sinks for Anthropogenic Carbon Physics Today August 2002 30-36 Composition of the Atmosphere More than 95% of all gases except radon reside in the atmosphere. The atmosphere controls the oceans gas contents for all gases except radon, CO2 and H2O. Gas Mole Fraction in Dry Air (fG) molar volume at STP (l mol-1 ) where fG = moles gas i/total moles N2 0.78080 22.391 O2 0.20952 22.385 Ar 9.34 x 10-3 22.386 CO2 3.3 x 10-4 22.296 Ne 1.82 x 10-5 22.421 He 5.24 x 10-6 22.436 Why is dry air used? Some comments about units of gases: In Air In Water Pressure - Atmospheres Volume - liters gas at STP / kgsw 1 Atm = 760 mm Hg STP = standard temperature and pressure Partial Pressure of Gasi = P (i) /760 = 1 atm and 0?C (= 273oK) Volume - liters gas / liters air Moles - moles gas / kgsw (ppmv = ml / l, etc) Conversion: lgas/kgsw / lgas / mole = moles/kgsw (~22.4 l/mol) Daltons Law Gas concentrations are expressed in terms of pressures. Total Pressure = SPi = Daltons Law of Partial Pressures PT = PN2 + PO2 + PH2O + PAr + Daltons Law implies ideal behavior -- i.e. all gases behave independently on one another (same idea as ideal liquid solutions with no electrostatic interactions). Gases are dilute enough that this is a good assumption. Variations in partial pressure (Pi) result from: 1) variations in PT (atmospheric pressure highs and lows) 2) variations in water vapor ( PH2O) We can express the partial pressure (Pi) of a specific gas on a dry