Trace gas exchange at the air/water interface: Measurements of mass accommodation coefficients

1990 ◽  
Vol 10 (4) ◽  
pp. 427-449 ◽  
Author(s):  
W. Kirchner ◽  
F. Welter ◽  
A. Bongartz ◽  
J. Kames ◽  
S. Schweighoefer ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Trace Gas ◽  
Water Interface ◽  
Air Water Interface ◽  
Accommodation Coefficients

scholarly journals Continuous measurement of air–water gas exchange by underwater eddy covariance

2017 ◽  
Vol 14 (23) ◽  
pp. 5595-5606 ◽  
Author(s):  
Peter Berg ◽  
Michael L. Pace
Keyword(s):  
Heat Flux ◽  
Gas Exchange ◽  
Exchange Rates ◽  
Eddy Covariance ◽  
High Speed ◽  
Heat Fluxes ◽  
Water Interface ◽  
O2 Concentration ◽  
Air Water Interface ◽  
Water Gas

Abstract. Exchange of gases, such as O2, CO2, and CH4, over the air–water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we used the aquatic eddy covariance technique – originally developed for benthic O2 flux measurements – right below the air–water interface (∼ 4 cm) to determine gas exchange rates and coefficients. Using an acoustic Doppler velocimeter and a fast-responding dual O2–temperature sensor mounted on a floating platform the 3-D water velocity, O2 concentration, and temperature were measured at high-speed (64 Hz). By combining these data, concurrent vertical fluxes of O2 and heat across the air–water interface were derived, and gas exchange coefficients were calculated from the former. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600) in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air–water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air–water heat fluxes) and not by biological activity (primary production and respiration). This physical control of gas exchange can be prevalent in lotic systems and adds uncertainty to assessments of biological activity that are based on measured water column O2 concentration changes. For example, in the 40 h deployment, there was near-constant river flow and insignificant winds – two main drivers of lotic gas exchange – but we found gas exchange coefficients that varied by several fold. This was presumably caused by the formation and erosion of vertical temperature–density gradients in the surface water driven by the heat flux into or out of the river that affected the turbulent mixing. This effect is unaccounted for in widely used empirical correlations for gas exchange coefficients and is another source of uncertainty in gas exchange estimates. The aquatic eddy covariance technique allows studies of air–water gas exchange processes and their controls at an unparalleled level of detail. A finding related to the new approach is that heat fluxes at the air–water interface can, contrary to those typically found in the benthic environment, be substantial and require correction of O2 sensor readings using high-speed parallel temperature measurements. Fast-responding O2 sensors are inherently sensitive to temperature changes, and if this correction is omitted, temperature fluctuations associated with the turbulent heat flux will mistakenly be recorded as O2 fluctuations and bias the O2 eddy flux calculation.

Accommodation coefficients for water vapor at the air/water interface

2004 ◽  
Vol 393 (1-3) ◽  
pp. 249-255 ◽  
Author(s):  
John Vieceli ◽  
Martina Roeselová ◽  
Douglas J Tobias
Keyword(s):  
Water Vapor ◽  
Water Interface ◽  
Air Water Interface ◽  
Accommodation Coefficients

Trace gas adsorption thermodynamics at the air−water interface: Implications in atmospheric chemistry

2009 ◽  
Vol 81 (10) ◽  
pp. 1889-1901 ◽  
Author(s):  
Kalliat T. Valsaraj
Keyword(s):  
Atmospheric Chemistry ◽  
Gas Adsorption ◽  
Trace Gas ◽  
Water Interface ◽  
Thermodynamic Equilibrium Constant ◽  
Structure Activity ◽  
Water Films ◽  
Ice Films ◽  
Air Water Interface ◽  
Polycyclic Aromatic

The thermodynamics of adsorption of gaseous organic compounds such as polycyclic aromatic hydrocarbons (PAHs) on water films is reviewed and discussed. The various experimental methods available to determine the thermodynamic equilibrium constant and the structure–activity relationships to correlate and estimate the same are reviewed. The atmospheric implications of the adsorption and oxidation of PAHs at the air–water interface of thin films of water such as existing in fog droplets, ice films, and aerosols are also enumerated.

scholarly journals Gas Exchange and Bubble-Induced Supersaturation in a Wind-Wave Tank

2004 ◽  
Vol 21 (12) ◽  
pp. 1925-1935 ◽  
Author(s):  
Peter Bowyer ◽  
David Woolf
Keyword(s):  
Steady State ◽  
Gas Exchange ◽  
Wind Wave ◽  
Relative Strength ◽  
Water Interface ◽  
Wave Tank ◽  
Gas Concentration ◽  
Gas Fluxes ◽  
Air Water Interface ◽  
Series Of Experiments

Abstract Gas exchange and bubble-induced supersaturation were measured in a wind-wave tank using total gas saturation meters. The water in the tank was subjected to bubbling using a large number of frits at a depth of 0.6 m. A simple linear model of bubble-mediated gas exchange implies that this should force an equilibrium supersaturation of 3%. This is confirmed by experiment, but a small additional steady-state supersaturation is also forced by warming. The total steady-state supersaturation is approached asymptotically. When the bubblers were switched off, the total gas pressure approached a new steady state at much lower supersaturation, at a rate that depended on the state of the wind and waves in the tank. The rates of approach on the various equilibria enabled the gas flux across the surface of the bubbles or across the air–water interface to be calculated. In addition a series of experiments was conducted where the water was subjected to bubbling in the presence of wind or wind and paddle waves: in this case gas invasion from the bubbles was balanced by gas evasion near or at the surface resulting in an equilibrium at <3% and enabling the relative strength of the invasion and evasion to be estimated. Gas concentrations could be measured in a rapid, automated manner using simple apparatus. To derive gas fluxes, corrections for changes in water temperature and fluctuations in air pressure are necessary, and these are quantified. In addition, transient fluctuations in gas concentration at the start of bubbling periods allowed mixing within the tank to be observed.

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