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Development of Advanced Hg Detection Using Cavity Ring-down Spectroscopy

Explore cutting-edge techniques for highly sensitive optical detection of elemental Hg in laboratory settings, enhancing speed, sensitivity, and specificity.

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Development of Advanced Hg Detection Using Cavity Ring-down Spectroscopy

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  1. Jim Burkholder NOAA ESRLChemical Sciences Division(James.B.Burkholder@noaa.gov) Laboratory Research: Development of instrumentation for cavity ring down spectroscopy detection of elemental Hg Trop. Chem. Group Tom Ryerson Tara Fortin Rebecca Washenfelder Adam Gianola Steve Brown Jim Meagher/A.R. Ravishankara

  2. Objectives for Laboratory Studies Develop Hg Optical Detection Methods (Field and Laboratory Applications) Issues: Speed/Sensitivity/Specificity * Cavity Ring-down Spectroscopy * Laser Induced Fluorescence Gas Phase Hg Kinetics * Key Reactions * Rate Coefficient Measurements 1 2

  3. Sample Out Sample In Mirror Purge Mirror Purge PMT lS lM CRD Laser Time (s) 0  Cavity Ring-down Spectroscopy * Direct Absorption Measurement * High Sensitivity Basic CRD Setup: Basic Equations: R(254 nm) ~ 0.996 0 ~ 1 s (266 nm coated mirrors) 61S0 63P1 Transition

  4. Cavity Ring-down Spectroscopy YAG Pumped Dye Laser Ring-down Cell and PMT

  5. Ringdown time (s) [Hg] ~ 3 x108 cm-3 Wavelength (nm) Previous Hg CRD Laboratory Studies Jongma et al. RSI 66, 2821, 1995 Open Cavity: 45 cm Laser: freq. doubled dye laser R = 0.997 @ 253.7 nm Spuler et al. App. Opt. 39, 2480, 2000 Semi-Open Cavity: 125 cm Laser: freq. doubled dye laser R = 0.9985 @ 253.7 nm Hg Sensitivity ~ 0.5 ppt (perm. Tube)

  6. CRD Measurements at NOAA Hg Ref.: 640 Torr (Zero Air) [Hg] = 6.8 x108 cm-3 Sensitivity S/N = 1 500 Shots  ≈ 1 x10-7 cm-1 [Hg] ≈ 3 x106 cm-3 Blank: 580 Torr (Zero Air) Good sensitivity for laboratory kinetic studies !

  7. Further Work ( Near Future ) Optimization of CRD Apparatus Mirror Characterization Better Mirrors (R > 0.996) Calibration and Sensitivity Measurements Inter-Comparison of Techniques (Trop. Chem. Group and Others) Comparison with commercial instruments Compare with Hg Calibration Standards Gas Phase Rate Coefficient Measurements Identify Chemistry (Input ?) Develop Laboratory Studies/Methods

  8. Further Work ( Near Future ) Photolysis Laser (248 nm) Crossed-PLP PMT ls = 4.7 cm CRD Laser CRD Laser Power Meter Discharge Flow wave PMT Additional Experimental Setups for Kinetic Studies

  9. Singlets Triplets 1S0 1P1 1D2 1F3 3S1 3P2 3P1 3P0 3D3 3D2 3D1 3F 0 8d 6f 8p 5f 9s 8p 7d 5f 8s 6d 10 8s 7p 7p 6d 434.75 578.97 576.96 7s 579.07 20 7s 365.01 365.48 312.57 296.73 6p 30 366.29 313.16 407.78 6p 40 50 184.96 60 253.652 70 Hg 80 6s 103 cm-1

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