Comparison of On-line and Off-line methods for the measurement of particle bound Reactive Oxygen Species

S J Fuller, F P H Wragg & M Kalberer

To characterize health-relevant properties of atmospheric aerosol particles a new on-line method for measurements of particle bound reactive oxygen species (ROS) reactivity was compared with a conventional off-line filter collection and extraction method. Both methods used the same 2-7 dichlorofluorescin (DCFH) and Horseradish Peroxidase (HRP) fluorescence probe assay to quantify ROS in oxidised organic aerosol. Off-line measurements were found to be seriously effected by the aerosol collection time, with ROS reactivity decreasing by up to a factor of five on a 15 minute timescale, thus suggested the fast time-resolved measurements provided by an on-line technique are essential for a better understanding of particle bound ROS activity and their effects on human health.

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