New Developments of a Laser-Induced Fluorescence Ground-Based Instrument for Measurements of Atmospheric Iodine Monoxide (IO)

Iodine monoxide (IO) plays a role in the photochemistry of the marine boundary layer and potentially acts as a catalyst to ozone loss in the stratosphere. The distribution of IO in vertical, horizontal, and temporal coordinates is unknown, severely limiting the understanding of the impact of IO on global photochemistry. To better understand the role IO plays in the atmosphere, additional measurements of IO are required. High sensitivity in situ measurements are required to detect IO because it is present at low mixing ratios (<10 ppt) and is spatially and temporally inhomogeneous. A laser-induced fluorescence instrument centered around a nanosecond Nd:YAG-pumped Ti:Sapphire laser system has been built to satisfy these requirements. Highly efficient fluorescence detection optics and photon counting techniques have yielded sensitivities of better than 0.1 ppt in 1 s for IO in the laboratory. Recent work has been focused on improvements to sensitivity, mechanical design, and data acquisition following an initial field deployment of a prototype instrument. New developments including an optical redesign of both the laser and detection systems as well as the design of a fully automated, ground-based instrument are presented.