Total mercury in ambient air can be collected in iodine monochloride, but the subsequent analysis is relatively complex and tedious, and contamination from reagents and containers is a problem. A sliver wool collector, preceded by a catalytic pyrolysis furnace, gives good recovery of mercury and simplifies the analytical step. An instrumental method based on particle counting proved unreliable, but another instrument using the 253.7 nm Hg optical absorption line proved to be quite accurate for the determination of elemental mercury in air. (NTIS)