The group is recognized for the development of a first-of-its-kind laser absorption spectrometer (LAS) and method for the direct determination of gaseous elemental mercury (GEM). The novel primary-direct method utilizes first principles of light-matter interaction physics to provide rapid, calibration-free measurement of mercury with traceability linkages to the SI. The accomplishment supports NIST calibration services by enabling rapid value assignment of NIST primary standard mercury/air generators, essential to serve U.S. industry in meeting its requirements to comply with the EPA Mercury and Air Toxics Standards regulatory guidelines for environmental protection.