Articles | Volume 7, issue 12
Atmos. Meas. Tech., 7, 4251–4265, 2014
Atmos. Meas. Tech., 7, 4251–4265, 2014

Research article 08 Dec 2014

Research article | 08 Dec 2014

Deployment of a sequential two-photon laser-induced fluorescence sensor for the detection of gaseous elemental mercury at ambient levels: fast, specific, ultrasensitive detection with parts-per-quadrillion sensitivity

D. Bauer1, S. Everhart1, J. Remeika1, C. Tatum Ernest1,*, and A. J. Hynes1 D. Bauer et al.
  • 1Division of Marine and Atmospheric Chemistry, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA
  • *currently at: Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. The operation of a laser-based sensor for gas-phase elemental mercury, Hg(0), is described. It utilizes sequential two-photon laser excitation with detection of blue-shifted laser-induced fluorescence (LIF) to provide a highly specific detection scheme that precludes detection of anything other than atomic mercury. It has high sensitivity, fast temporal resolution, and can be deployed for in situ measurements in the open atmosphere with essentially no perturbation of the environment. An ambient sample can also be pulled through a fluorescence cell, allowing for standard addition calibrations of the concentration. No type of preconcentration is required and there appears to be no significant interferences from other atmospheric constituents, including gas-phase oxidized mercury species. As a consequence, it is not necessary to remove oxidized mercury, commonly referred to as reactive gaseous mercury (RGM), from the air sample. The instrument has been deployed as part of an instrument intercomparison and compares well with conventional instrumentation that utilizes preconcentration on gold followed by analysis using cold-vapor atomic fluorescence spectroscopy (CVAFS). Currently, the achievable detection sensitivity is ~ 15 pg m−3 (~ 5 × 104 atoms cm−3, ~ 2 ppq) at a sampling rate of 0.1 Hz, i.e., averaging 100 shots with a 10 Hz laser system. Preliminary results are described for a 50 Hz instrument that utilizes a modified excitation sequence and has monitored ambient elemental mercury with an effective sampling rate of 10 Hz. Additional work is required to produce the precision necessary to perform eddy correlation measurements. Addition of a pyrolysis channel should allow for the measurement of total gaseous mercury (TGM) and hence RGM (by difference) with good sensitivity and time resolution.

Short summary
An understanding of the biogeochemical cycling of mercury is an important health issue. Exposure to mercury is primarily through fish consumption. The typical background concentration of Hg(0) is ~200 ppq; hence atmospheric measurements represent a significant challenge in ultratrace analytical chemistry. We developed a laser-based sensor for detection of gas-phase elemental mercury, Hg(0), that is capable of fast in-situ measurements at ambient levels and can also measure oxidized mercury.