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.