Abstract
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.
Highlights
A detailed understanding of the biogeochemical cycling of mercury and the routes to the production of organomercury compounds in ecosystems is a critical issue from a human health perspective
An ambient sample can be pulled through a fluorescence cell, allowing for standard addition calibrations of the concentration
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)
Summary
A detailed understanding of the biogeochemical cycling of mercury and the routes to the production of organomercury compounds in ecosystems is a critical issue from a human health perspective. Reductions in mercury emissions have been the focus of global negotiations that have led to the Minimata Convention on Mercury, a multilateral environmental agreement that has been signed by 97 countries (UNEP, 2014) These developments take place in a situation in which our overall understanding of the chemistry of atmospheric mercury transformation is limited (Hynes et al, 2008; Subir et al, 2011, 2012; Gustin and Jaffe, 2010). Current approaches to the measurement of both elemental and oxidized mercury at ambient levels rely exclusively on instruments that use preconcentration on gold followed by analysis using coldvapor atomic fluorescence spectroscopy (CVAFS). The development of a fast in situ sensor capable of measuring Hg(0) at ambient levels is a critical research need Such a sensor can independently verify the performance of the CVAFS instruments. We show preliminary results from a “secondgeneration” 2P-LIF system that utilizes a different excitation scheme
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
