An enclosure technique for measuring nonmethane organic compound emissions from grasslands

A static chamber technique for measuring emissions of nonmethane organic compounds (NMOCs) from soil surfaces and herbaceous vegetation in a natural setting has been developed. The technique involves the insertion of a polymethyl methacrylate frame into the ground. A polycarbonate chamber is placed in a water-containing trough on the frame to seal the chamber to the surface. The soil surface and vegetation are covered for various lengths of time, and samples of the chamber air are passively collected in preevacuated stainless steel canisters. The samples are analyzed in the laboratory by a whole-air cryogenic-preconcentration/high-resolution gas chromatographic technique with flame ionization detection. Changes in the concentrations of the NMOCs with time in the chamber are used to derive emission rates. The technique is sensitive and precise, but the occasional observation of nonlinear changes in NMOC concentrations in the chamber with the length of the covering period limits the accuracy of emission rates derived by this technique. Despite this Limitation, the method is effective for identifying NMOC emissions and investigating seasonal variations of emission rates.