Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions

摘要

Nitrate radical (NO3^•) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO3^• 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 NO3^• supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N2O5 and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO3^• loss through the system, consistency of the NO3^• concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).