[Gas Transfer Velocity of CH₄ at Extremely Low Wind Speeds]

Thin boundary theory equation (TBL) is widely used to determine gas fluxes across water-air interfaces, and the gas transfer velocity (k₆₀₀) is the key environmental factor in the equation. A monthly field campaign was carried out during one year to measure CH₄ flux and to probe its exchange rate across the air-water interface in a drinking reservoir and 5 adjacent ponds. The ranges of wind speed and surface water temperature were 0-0.75 m·s^-1 and 6.3-30.9℃respectively, and their average values were 0.19 m·s^-1 and 19.3℃ respectively. The gas transfer velocity of CH₄ varied from 0.20 to 1.99 cm·h^-1 with an average of 0.50 cm·h^-1. Correlation functions between the gas transfer velocity and the wind speed at 10 m height (U₁₀) and surface water temperature (T_w) were given here to quantify k₆₀₀. There were significant correlations between the fitted values and actual values both for original and bin-averaged data.