An automated online instrument to quantify aerosol-bound reactive oxygen species (ROS) for ambient measurement and health-relevant aerosol studies

Francis P H Wragg,Frank J Kelly,Ray Freshwater,David C Green,Markus Kalberer,Stephen J Fuller

doi:10.5194/amt-9-4891-2016

Francis P H Wragg, Frank J Kelly + Show 4 more

Open Access

https://doi.org/10.5194/amt-9-4891-2016

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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-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 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 or days. From laboratory measurements, the instrument was found to have a detection limit of ∼ 4 nmol [H2O2] equivalents per cubic metre (m3) air, a dynamic range up to at least ∼ 2000 nmol [H2O2] equivalents per m3 air and a time resolution of ≤ 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 [H2O2] equivalents per m3 air were detected with PM2.5 concentrations up to 28 µg m−3. 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.

Highlights

The adverse health effects associated with atmospheric aerosol particles have been well documented in epidemiological studies and further supported with biological cell culture/in vivo studies; there is a widely accepted association between higher ambient aerosol particle levels and increases in hospital admissions and deaths due to respiratory disease, cardiovascular disease and cancer (Brunekreef and Holgate, 2002; Dockery et al, 1993; Kunzi et al, 2013; Laden et al, 2006; Lepeule et al, 2012)
We introduce a new portable instrument to allow online, continuous measurement of particle-bound reactive oxygen species (ROS) using a chemical assay of 2 7 -dichlorofluorescein (DCFH) with horseradish peroxidase (HRP), via fluorescence spectroscopy
ROS are often not stable or long-living (e.g. ROOH, R·, RO·x species in particular), so such slow and time-consuming offline processes may not be best suited to determine their atmospheric concentrations, leading to potentially significant underestimates of ROS concentrations. This is supported by an earlier study in which we showed ROS concentrations in laboratorygenerated oxidised organic aerosol decreased by a factor of 5–10 within 15 min of collection of a sample on a filter, suggesting offline techniques may fail to capture the short-lived, labile, fraction of ROS, instead capturing only the longerlived, less labile, fraction (Fuller et al, 2014)

Summary

Introduction

The adverse health effects associated with atmospheric aerosol particles have been well documented in epidemiological studies and further supported with biological cell culture/in vivo studies; there is a widely accepted association between higher ambient aerosol particle levels and increases in hospital admissions and deaths due to respiratory disease, cardiovascular disease and cancer (Brunekreef and Holgate, 2002; Dockery et al, 1993; Kunzi et al, 2013; Laden et al, 2006; Lepeule et al, 2012). Due to the large variability in ambient particulate matter, it is still unclear which physical or chemical properties are most important for these negative health effects. Previous studies have suggested particle size, transition metal levels and elemental carbon levels to be bet-. Wragg et al.: An automated online instrument to quantify aerosol-bound ROS ter indicators than simple particle mass concentration (Godri et al, 2010; Kelly and Fussell, 2012; Koike and Kobayashi, 2006; Oberdorster et al, 2005)

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