Airborne-mercury detection by resonant UV laser pumping

Area of Science:

• Atomic Physics
• Environmental Science
• Spectroscopy

Background:

• Laser-induced fluorescence (LIF) is a sensitive technique for detecting atomic species.
• Mercury (Hg(0)) detection is crucial for environmental monitoring due to its toxicity.
• Existing methods for airborne mercury detection have limitations in sensitivity or real-time monitoring.

Purpose of the Study:

• To investigate the potential of optical pumping of Hg(0) for enhanced LIF and ionization detection.
• To evaluate the feasibility of using these phenomena for elemental airborne mercury monitoring.
• To determine the achievable sensitivities for mercury detection using the developed methods.

Main Methods:

• Optical pumping of the Hg(0) 253.7 nm transition using a laser.
• Detection of laser-induced fluorescence (LIF) at the 546.2 nm green transition.
• Simultaneous monitoring of ionization signals.
• Measurements conducted at reduced background air pressures (0.1 Torr).

Main Results:

• Observed fast energy transfer and strong LIF from a non-directly populated green transition.
• Significant ionization signals correlated with multiphoton processes and electron collisional excitation.
• Achieved preliminary sensitivities of 2 and 10 parts per billion (ppb) for LIF and ionization, respectively.
• Projected sensitivities of 1 x 10(-4) and 1 x 10(-5) ppb with system optimization.

Conclusions:

• Optical pumping of Hg(0) coupled with LIF and ionization offers a promising approach for sensitive airborne mercury detection.
• The observed phenomena, including multiphoton excitation and electron collisional excitation, are key to the high sensitivity.
• Further system optimization can significantly enhance detection limits for environmental mercury monitoring.