An online monitor of the oxidative capacity of aerosols (o-MOCA).

Arantzazu Eiguren-Fernandez,Nathan Kreisberg,Susanne Hering

doi:10.5194/amt-10-633-2017

Arantzazu Eiguren-Fernandez, Nathan Kreisberg + Show 1 more

Open Access

https://doi.org/10.5194/amt-10-633-2017

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Abstract

The capacity of airborne particulate matter to generate reactive oxygen species (ROS) has been correlated with the generation of oxidative stress both in vitro and in vivo. The cellular damage from oxidative stress, and by implication with ROS, is associated with several common diseases, such as asthma and chronic obstructive pulmonary disease (COPD), and some neurological diseases. Yet currently available chemical and in vitro assays to determine the oxidative capacity of ambient particles require large samples, analyses are typically done offline, and the results are not immediate.Here we report the development of an online monitor of the oxidative capacity of aerosols (o-MOCA) to provide online, time-resolved assessment of the capacity of airborne particles to generate ROS. Our approach combines the Liquid Spot Sampler (LSS), which collects particles directly into small volumes of liquid, and a chemical module optimized for online measurement of the oxidative capacity of aerosol using the dithiothreitol (DTT) assay. The LSS uses a three-stage, laminar-flow water condensation approach to enable the collection of particles as small as 5 nm into liquid. The DTT assay has been improved to allow the online, time-resolved analysis of samples collected with the LSS but could be adapted to other collection methods or offline analysis of liquid extracts.The o-MOCA was optimized and its performance evaluated using the 9,10-phenanthraquinone (PQ) as a standard redox-active compound. Laboratory testing shows minimum interferences or carryover between consecutive samples, low blanks, and a reproducible, linear response between the DTT consumption rate (nmol min−1) and PQ concentration (μM). The calculated limit of detection for o-MOCA was 0.15 nmol min−1. The system was validated with a diesel exhaust particle (DEP) extract, previously characterized and used for the development, improvement, and validation of the standard DTT analysis. The DTT consumption rates (nmol min−1) obtained with the o-MOCA were within experimental uncertainties of those previously reported for these DEP samples. In ambient air testing, the fully automated o-MOCA was run unattended for 3 days with 3 h time resolution and showed a diurnal and daily variability in the measured consumption rates (nmol min−1 m−3).

Highlights

There is ample evidence linking exposure to particulate air pollution to adverse health effects, the mechanisms that lead to those effects are not completely understood
A sampling flow rate of 3.0 L min−1 was selected to run the Liquid Spot Sampler to maximize the air sample volume collected without compromising the high collection efficiency over a wide range of particle sizes
For the 3.0 L min−1 sampling flow rate used with the o-MOCA, 500 μL was selected as the volume for optimum liquid collection

Summary

Introduction

There is ample evidence linking exposure to particulate air pollution to adverse health effects, the mechanisms that lead to those effects are not completely understood. The oxidative potential of airborne particles is attributed to their chemical composition (organics, trace metals; Eiguren-Fernandez et al, 2010; Ercal et al, 2001; Jomova and Valko, 2011; Chien et al, 2009; Hawley et al, 2014) and to their physical characteristics (particle size, shape, etc.; Bünger et al, 2000; Chien et al, 2009; de Haar et al, 2006; Wessels et al, 2010) Trace metals, such as copper and iron, can generate ROS via Fenton chemistry, while organics, including polycyclic aromatic hydrocarbons (PAHs) and quinones, generate ROS via metabolic transformations (Chung et al, 2006; Kumagai et al, 2012; Ercal et al, 2001; Valko et al, 2005)

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