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Comparison of on-line and off-line methods to quantify reactive oxygen species (ROS) in atmospheric aerosols
Atmospheric aerosol particle concentrations have been linked with a wide range of pulmonary and cardio-vascular diseases but the particle properties responsible for these negative health effects are largely unknown. It is often speculated that reactive oxygen species (ROS) present in atmospheric particles lead to oxidative stress in, and ultimately disease of, the human lung. The quantification of ROS is highly challenging because some ROS components such as radicals are highly reactive and therefore short-lived. Thus, fast analysis methods are likely advantageous over methods with a long delay between aerosol sampling and ROS analysis. We present for the first time a detailed comparison of conventional off-line and fast on-line methods to quantify ROS in organic aerosols. For this comparison a new and fast on-line instrument was built and characterized to quantify ROS in aerosol particles with high sensitivity and a limit of detection of 4 nmol H2O2 equivalents per m3 air. ROS concentrations are measured with a time resolution of approximately 15 min, which allows the tracking of fast changing atmospheric conditions. The comparison of the off-line and on-line method shows that, in oxidized organic model aerosol particles, the majority of ROS have a very short lifetime of a few minutes whereas a small fraction is stable for a day or longer. This indicates that off-line techniques, where there is often a delay of hours to days between particle collection and ROS analysis, may severely underestimate true ROS concentrations and that fast on-line techniques are necessary for a reliable ROS quantification in atmospheric aerosol particles and a meaningful correlation with health outcomes.This work was supported by the Natural Environment Research Council (NE/H52449X/1), the Velux Stiftung (Project 593) and an ERC starting grant (grant no. 279405).This is the accepted manuscript version. The final published version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S1352231014002787
An automated online instrument to quantify aerosol-bound reactive oxygen species (ROS) for ambient measurement and health-relevant aerosol studies
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-intensive, give poor temporal resolution and generally have significant delays between aerosol sampling and ROS analysis. However, many oxidising 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 online, continuous measurement of particle-bound ROS using a chemical assay of 27-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 or days.
From laboratory measurements, the instrument was found to have a detection limit of ~4 nmol [HO] equivalents per cubic metre (m) air, a dynamic range up to at least ~2000 nmol [HO] equivalents per m air and a time resolution of β€ 12 min. The instrument allows for ~16 h 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 [HO] equivalents per m air were detected with PM concentrations up to 28 Β΅g m.
The new and portable Online 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 conditions, especially in urban environments. The instrument design allows for automated operation and extended field operation with twice-daily presence of an operator. As well as having sensitivity suitable for ambient level measurement, the instrument is also suitable at concentrations such as those required for laboratory and chamber toxicological studies.The authors would like to thank ERC (the European Research Council, grant no. 279405) for their funding of this study. Infrastructure at Marylebone Road was supported by NERC (the Natural Environment Research Council, Clearflo grant no. NE/H003231/1) and Defra (Department of Environment Food and Rural Affairs, contract AQ0643 Automatic London Network (2010-14) RMP 5442)