Automated HCl laser monitor for long term and flight deployments

Tropospheric oxidation capacity is dominated by HOx photochemistry, however halogen atoms and oxides significantly affect these chemical cycles. A sensitive and robust measurement of gaseous HCl is critically important to improve our understanding of halogen chemistry and its impacts on the spatial and temporal oxidation capacity of the atmosphere. This is vital to evaluating the life time of short lived radiative forcers and understanding air quality in continental and coastal cities. We will combine two innovations to create a novel trace gas monitor that can sensitively (15 ppt noise at 1 Hz) and continuously monitor HCl at remote field sites and from flight platforms with little or no user intervention. First, we will use a recently commercialized ICL laser to probe one of the strongest HCl rovibrational transitions. Second, we will extend our patented active passivation technique from HNO3 to HCl, enabling HCl sampling with minimal surface interactions despite its stickiness. HCl can be detected with chemical ionization mass spectrometry but our approach will require far less user intervention and almost no calibration. During Phase I we will build a prototype instrument, an HCl source and an actively passivated inlet to demonstrate the feasibility of this technique.