Abstract Number: 19 Working Group: Instrumentation and Methods
Abstract We have developed a laboratory prototype of an on-line, field-deployable instrument for the time-resolved quantification of the capacity of airborne particles to generate reactive oxygen species (ROS). Our approach adapts the widely accepted dithioerythreitol (DTT) redox assay to on-line analysis of concentrated samples of airborne particles collected directly into sub-milliliter volumes of liquid using our firm’s condensationally-enhanced particle collection technology. The on-line Monitor of the Oxidative Capacity of Airborne Particulate Matter (o-MOCA) consists of a liquid collector coupled to a chemical module where the DTT analysis is conducted in-situ. The liquid collector is uniquely capable of collecting both soluble and insoluble constituents of airborne particles, and employs moderate temperatures to achieve particle growth, so that the sample is never subjected to temperatures above approximately 35 ̊C. The standard DTT assay has been modified for fast (30 min) analysis and coupled to the liquid collector for programmed sample transfer. The concentrated nature of the suspension allows measuring the oxidative potential of particulate matter with time resolution of a few hours.
The system was optimized and tested using 9,10-Phenanthroquinone (PQ). A linear response in DTT consumption rate (µM/min) with PQ concentration was obtained. The o-MOCA chemical module was validated using a diesel exhaust particle (DEP) extract, which has been well characterized over the years and used for the development and validation of the standard DTT analysis (provided courtesy of Dr. Arthur Cho; University of California at Los Angeles). This extract has bee. The DTT consumption rates (nmol/min) obtained with the o-MOCA were within experimental uncertainties of those reported by the UCLA group over a range of DEP concentrations. Our fully automated o-MOCA prototype was operated unattended for 3 days, collecting and analyzing 3-hr ambient particulate matter samples.