In situ detection of atomic and molecular iodine using Resonance and Off-Resonance Fluorescence by Lamp Excitation: ROFLEX

摘要

We demonstrate a new instrument for in situ detection of atmospheric iodineatoms and molecules based on atomic and molecular resonance andoff-resonance ultraviolet fluorescence excited by lamp emission. Theinstrument combines the robustness, light weight, low power consumption andefficient excitation of radio-frequency discharge light sources with thehigh sensitivity of the photon counting technique. Calibration of I₂fluorescence is achieved via quantitative detection of the molecule byIncoherent Broad Band Cavity-enhanced Absorption Spectroscopy. Atomic iodinefluorescence signal is calibrated by controlled broad band photolysis ofknown I₂ concentrations in the visible spectral range at atmosphericpressure. The instrument has been optimised in laboratory experiments toreach detection limits of 1.2 pptv for I atoms and 13 pptv for I₂, forS/N = 1 and 10 min of integration time. The ROFLEX system has beendeployed in a field campaign in northern Spain, representing the firstconcurrent observation of ambient mixing ratios of iodine atoms andmolecules in the 1–350 pptv range.