An Automated On-line Instrument to Quantify Aerosol-Bound Reactive Oxygen Species (ROS) for Ambient Measurement and Health Relevant Aerosol Studies

Abstract

Abstract. The adverse health effects associated with ambient aerosol particles have been well documented, but it is still unclear which aerosol properties are most important for their negative health impact. Some studies suggest the oxidative effects of particle bound reactive oxygen species (ROS) are potential major contributors to the toxicity of particles. Traditional ROS measurement techniques are labour intense, give poor temporal resolution, and generally have significant delays between aerosol sampling and ROS analysis. However, many oxidizing particle components are reactive and thus potentially short lived. Thus, a technique to quantify particle-bound ROS online would be beneficial to quantify also the short-lived ROS components. We introduce a new portable instrument to allow on-line, continuous measurement of particle-bound ROS using a chemical assay of 2'7'-dichlorofluorescein (DCFH) with horseradish peroxidase (HRP), via fluorescence spectroscopy. All components of the new instrument are attached to a containing shell, resulting in a compact system capable of automated continuous field deployment over many hours to days. From laboratory measurements, the instrument was found to have a detection limit of ~4 nmol[H2O2]equivalents per m3 air, a dynamic range up to at least ~2000 nmol[H2O2]equivalents per m3 air, and a time resolution under 12 minutes. The instrument allows for ~12 hours automated measurement if unattended, and shows a fast response to changes in concentrations of laboratory-generated oxidised organic aerosol. The instrument was deployed at an urban site in London and particulate ROS levels of up to 24 nmol[H2O2]equivalents per m3 air were detected with PM2.5 concentrations up to 28 μg m-3. The new and portable On-line Particle-bound ROS Instrument (OPROSI) allows fast-response quantification; this is important due to the potentially short-lived nature of particle-bound ROS as well as fast changing atmospheric onditions, especially in urban environments. The instrument design allows for automated operation and extended field operation. As well as having sensitivity suitable for ambient level measurement, the instrument is also suitable at concentrations such as those required for toxicological studies.