Some potential errors in the measurement of mercury gas exchange at the soil surface using a dynamic flux chamber

A series of controlled environment experiments were conducted to examine the use of a dynamic flux chamber to measure soil emission and absorption of total gaseous mercury TGM.. Uncertainty about the appropriate airflow rates through the chamber and chamber exposure to ambient wind are shown to be major sources of potential error. Soil surface mercury flux measurements over a range of chamber airflow rates showed a positive linear relationship between flux rates and airflow rate through the chamber. Mercury flux measurements using the chamber in an environmental wind tunnel showed that exposure of the system to ambient winds decreased the measured flux rates by 40% at a wind speed of 1.0 m sy1 and 90% at a wind speed of 2 m sy1. Wind tunnel measurements also showed that the chamber footprint was limited to the area of soil inside the chamber and there is little uncertainty of the footprint size in dry soil.