LAUSR

We present a primary method for absolute reference material-free measurement of gaseous elemental mercury mass concentration based on laser absorption spectroscopy at wavelengths near 254 nm and anchored to the international system of units. A 76 m-long multipass cell provides a detection limit of 1 ng m-3 for an averaging time of 8 min. A dual-cell arrangement, comprising a single-pass and a multipass cell, provides a dynamic range of six decades and spans from ambient to emission levels of gaseous elemental mercury (1 ng m-3 to 1000 μg m-3). The relative standard uncertainty of the measurement is 0.5% in the 0.25 to 1000 μg m-3 range.