Theory and laboratory study of a tall passive chamber for measuring gas fluxes at soil surface

A tall passive flux chamber with a height significantly greater than its ho rizontal dimensions is proposed for measuring fluxes of volatile organic co mpounds (VOCs) at the soil surface. The main feature of this tall chamber i s the presence of a vertical concentration gradient of the target gas in th e chamber. The emission and transport behavior of the target gas in the soi l-chamber system are analyzed using the diffusion theory. A mathematical mo del is developed to estimate the flux from the soil into the tall chamber, providing the target gas establishes a detectable vertical concentration gr adient in the chamber. To obtain the data required for calculating flux, on ly two gas concentrations (C-1 and C-2) at two heights (h(1) and h(2)) with in the chamber need to be measured at the end of a short chamber placement time (t(p)). To evaluate the applicability of the tall chamber for measurin g flux, several laboratory tests have been conducted, using CH2Cl2 and CH3B r as the target gases. The results indicate that the proposed tall chamber has promising potential as a method for measuring fluxes of VOCs at the soi l surface.