Effects of changes in environmental conditions on atmospheric mercury exchange: Comparative analysis from a rice paddy field during the two spring periods of 2001 and 2002

Abstract

The environmental mobilization characteristics of Hg were investigated in a rice paddy field in the Hari district of Kang Hwa Island, Korea during two field campaigns held in late March 2001 and late April 2002. In the course of these two field campaigns, we measured the concentration, concentration gradients (between two different heights of 1 and 5 m), and fluxes of Hg with the aid of micrometeorological approaches. The results of our experiments consistently indicate that the study area behaved as both source and sink of Hg, yielding a net emission rate of 183 (1st) to 28 ng m−2 h−1 (2nd campaign). It was however found that the soil‐air exchange patterns of Hg during the two study periods, although investigated in similar seasonal cycles, contrast to a large extent. Upward emission prevailed in both the frequency and magnitude during the 1st study period, but dry deposition was seen more dominantly in terms of frequency during the 2nd study period. In light of the fact that the occurrence patterns of Asian Dust events differed greatly between the two study periods, the possible role of long‐range transport of airborne pollutants (LRTAP) as sources of Hg into the study area has also been examined using information on air mass movement patterns. Because observed differences in Hg flux patterns generally reflect changes in environmental conditions across study periods, the bi‐directional exchange patterns of Hg during the two field campaigns were explained in relation to highly diverse environmental conditions that persisted in each study period.