In situ detection of atomic and molecular iodine using resonance and off-resonance fluorescence by lamp excitation: ROFLEX

Abstract

We demonstrate a new instrument for in situ detection of atmospheric iodine atoms and molecules based on atomic and molecular resonance and off-resonance ultraviolet fluorescence excited by lamp emission. The instrument combines the robustness, light weight, low power consumption and efficient excitation of radio-frequency discharge light sources with the high sensitivity of the photon counting technique. Calibration of I<sub>2</sub> fluorescence is achieved via quantitative detection of the molecule by incoherent broad band cavity-enhanced absorption spectroscopy. Atomic iodine fluorescence signal is calibrated by controlled broad band photolysis of known I<sub>2</sub> concentrations in the visible spectral range at atmospheric pressure. The instrument has been optimised in laboratory experiments to reach detection limits of 1.2 pptv for I atoms and 20 pptv for I<sub>2</sub>, for S/N=1 and 10 min of integration time. The ROFLEX system has been deployed in a field campaign in Northern Spain, representing the first concurrent observation of ambient mixing ratios of iodine atoms and molecules in the 1–350 pptv range