【热对流对高渗透性土壤中陆-气边界层CO2通量的影响】Yonatan Ganot^{a 1} Maria I. Dragila^b Noam Weisbrod^a . Impact of thermal convection on CO₂flux across the earth–atmosphere boundary in high-permeability soils. Agricultural and Forest MeteorologyVolume 184 15 January 2014 Pages 12–24

Abstract

Quantifying earth–atmosphere gas exchange is a challenging yet important problem that is made more complicated by the large number of mechanisms that contribute to this process. This work investigates one mechanism controlling non-diffusive gas transport from high-permeability media that is driven by natural diurnal thermal gradients in the upper vadose zone. We quantified CO₂ migration through 1-m long columns packed with two different permeability values: sand and large soil aggregates – both dry to eliminate chemical reactions. The bottom ends of the columns were exposed to 2000 ppm CO₂-enriched air and the CO₂ concentration profiles along the columns was continually monitored. The columns were exposed to two different thermal regimes: isothermal conditions and a range of typical nighttime thermal gradients that are known to lead to unstable gas density profiles. Under isothermal conditions and regardless of the matrix air-permeability diffusion was the major mechanism for surface–atmosphere gas exchange. Under nighttime conditions the prevailing mechanism depended upon matrix air-permeability: diffusion controlled CO₂ transport in the low permeability matrix whereas thermal convection dominated transport in the high permeability matrix. Venting by thermal convection caused a CO₂ flux of up to two orders of magnitude higher than the diffusive flux. Such a mechanism may be implicated in a number of environmental settings. In soil thermally driven convection can contribute to soil aeration influencing ro