An examination of methods for the measurements of reactive gaseous mercuryin the atmosphere

Reactive gaseous Hg (RGHg), usually assumed to be HgCl2, may dominate the t otal Hg depositional flux due to its higher surface reactivity and water so lubility. Three methods are currently used for RGHg sampling: multistage fi lter packs, refluxing mist chambers, and KCl-coated denuders, but none of t hese methods are considered standard. Field comparisons were performed at C hesapeake Biological Laboratory (CBL) to test if these methods could give c omparable results. Mist chambers and denuders were operated continuously fo r 24 h in some cases to observe the diurnal variation. All methods demonstr ated the dynamic fluctuation of atmospheric RGHg, ranging from a few picogr ams per cubic meter to more than 500 pg/m(3), These methods also reported s imilar temporal RGHg trends. At low RGHg levels, the denuder tended to repo rt higher values of RGHg relative to the filter back, while mist chamber Va lues were generally in agreement with the filter pack. Discrepancy among me thods was more significant under higher RGHg levels. Considering the uncert ainties associated with these methods, our data suggest that these methods did produce comparable results. The 24-h continuous measurements showed tha t RGHg was usually undetectable at night. However, our data also suggest fa ctors in addition to photochemistry, such as movement and mixing of air mas ses, are influencing the distribution of RGHg at CBL.