title: Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions.
abstract: Nitrate radical (NO(3)(●)) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO(3)(●) at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50-500 ppt, ±30 ppt) and flow rates (500-2000 ml min(-1)) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO(3)(●) supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N(2)O(5) and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO(3)(●) loss through the system, consistency of the NO(3)(●) concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).
authors.affiliation: Exposure Assessment Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, West Virginia 26505, USA.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Flemmer
authors.forename: Jason E
authors.initials: JE
authors.lastname: Ham
mesh_terms: D001331:Automation; D005246:Feedback; D005609:Free Radicals / Q000737:chemistry; D006813:Humidity; D009566:Nitrates / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry; D011138:Polytetrafluoroethylene / Q000737:chemistry; D013057:Spectrum Analysis / Q000295:instrumentation*; D055549:Volatile Organic Compounds / Q000737:chemistry
chemical_list: D005609:Free Radicals; D009566:Nitrates; D009589:Nitrogen Oxides; D055549:Volatile Organic Compounds; C010125:nitrogen pentoxide; D011138:Polytetrafluoroethylene