A micrometeorological method (REA) has been implemented to assess the role of cereal crop fields in the North China Plain as a source or sink of elemental mercury vapor (Hg0
) during the course of a full year. In combination with chamber measurements under the canopy, the above-canopy REA measurements provided evidence for a balance between Hg0
ground emissions and uptake of Hg0
by the crop foliage, with net emissions prevailing from the ecosystem during the majority of a year.