An automated online 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-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 [H 2 O 2 ] equivalents per cubic metre (m 3 ) air, a dynamic range up to at least ∼ 2000 nmol [H 2 O 2 ] equivalents per m 3 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 [H 2 O 2 ] equivalents per m 3 air were detected with PM 2.5 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 particlebound 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.

Multiphase composition changes and reactive oxygen species formation during limonene oxidation in the new Cambridge Atmospheric Simulation Chamber (CASC)

“…A new OPROSI, described in Wragg et al (2016), is used to continuously monitor this health-relevant property of aerosols from the chamber. The continuous sample inflow (5 L min −1 ) passes through a PM 2.5 cyclone (URG-2000-30E-5-2.5-S) and charcoal denuder prior to entering into a particle-into-liquid sampler (PILS).…”

“…OPROSI has a time resolution of 4 min (e-folding time during online particle collection tests) and is thus able to capture most timedependant processes observed during SOA formation and evolution. This instrument is especially sensitive to shortlived ROS components, which react within seconds-minutes after sampling (Wragg et al, 2016). The EESI-MS, PTR-MS, and OPROSI are all placed in a laboratory just next the room that houses the chamber.…”

“…Together these complementary techniques produce a detailed, highly time-resolved picture of the evolving organic components in the chamber on a molecular level. In parallel, an Online Particle-bound Reactive Oxygen Species Instrument (OPROSI) (Wragg et al, 2016) allows the healthrelevant oxidising potential of organic species to be quantified with high time resolution.…”

Development, characterization and first deployment of an improved online reactive oxygen species analyzer

“…Accurate ROS quantification remains challenging because some ROS are highly reactive and are likely at least partially degraded prior to measurement when using offline techniques, which typically have delays of hours, days or weeks. Therefore, online techniques (through direct sampling into the liquid phase and measurement within a few minutes) are necessary for reliable ROS quantification (Wragg et al, 2016).…”

Author response to Reviewer 1, Gallimore et al., (2017)

“…ROS can be associated with the negative health impacts of aerosols (den Hartigh et al, 2010;Steenhof et al, 2011). A new OPROSI, described in Wragg et al (2016), is used to continuously monitor this health-relevant property of aerosols from the chamber. The continuous sample inflow (5 L min −1 ) passes through a PM 2.5 cyclone (URG-2000-30E-5-2.5-S) and charcoal denuder prior to entering into a particle-into-liquid sampler (PILS).…”