A novel spectroscopic approach for detection of chlorine reservoir species: HCl-TILDAS

Atomic chlorine radicals are known to affect atmospheric oxidation and pollutant lifetimes, but are challenging to detect due to their low ambient concentrations.  A lack of field observations limits useful assessments of the impacts of tropospheric chlorine oxidation on important atmospheric processes, such as regional ozone production, reactive nitrogen loss, and global methane removal.  In the last decade, instrumental innovations have enabled detection and speciation of much more stable chlorine atom reservoir species, such as nitryl chloride, through techniques such as cavity ring down spectroscopy and mass spectrometry.  HCl is the most abundant and long-lived tropospheric chlorine reservoir species, yet few observations exist.  Here, we present a specific method for detection of HCl via Tunable Laser Infrared Direct Absorption Spectrometer (TILDAS), which has been further extended for the detection of nitryl chloride.  This analytical method has several advantages over current observational techniques (e.g. chemical ionisation mass spectrometry), and will provide a much needed constraint on the tropospheric chlorine atom budget.