Developing an instrument to quantify aerosol toxicity

Large-scale epidemiological studies have consistently shown that exposure to
ambient particulate matter (PM) is responsible for a variety of adverse health
effects. However, the specific physical and chemical properties of particles that
are responsible for observed health effects, as well as the underlying mechanisms
of particle toxicity upon exposure, remain largely uncertain. Studies have widely
suggested that the oxidative potential (OP) of aerosol particles is a key metric
to quantify particle toxicity. OP is defined as the ability of aerosol particle
components to produce reactive oxidative species (ROS) and deplete antioxidants
in vivo.
Traditional methods for measuring OP using acellular assays largely rely on
analyzing PM collected in filters offline. This is labor intensive and involves a
substantial time delay between particle collection and OP analysis. It therefore
likely underestimates particle OP, because many reactive chemical components
which are contributing to OP are short-lived and therefore degrade prior to offline
analysis. We investigated these differences in online and offline measurements
with different acellular assays and with cellular methods and could show that for
biogenic secondary organic aerosol (SOA), a large fraction decays within minutes
to hours.
Thus, new techniques are required to provide a robust and rapid quantification
of particle OP, capturing the chemistry of oxidizing and short-lived highly
reactive aerosol components and their concentration dynamics in the atmosphere.
To address these measurement shortcomings, we developed a portable online
instrument that directly samples particles into an ascorbic acid-based assay under
physiologically relevant conditions of pH 6.8 and 37 °C, providing continuous
accurate OP measurements with a high time resolution (5 min). This online
oxidative potential ascorbic acid instrument (OOPAAI) runs autonomously for
up to three days and has a detection limit of about 5 μg/m3 in an urban environ-
ment, which allows the characterization of particle OP, even in low-pollution areas.
With this novel instrument, we not only measured ambient aerosol, but also
conducted various laboratory campaigns where we investigated the toxicity of
various aerosol systems. Primary and secondary emissions with different aging
times from car exhaust were measured and compared to primary and secondary
aerosols from residential wood combustion, showing a higher toxicity for residential
wood combustion for primary and secondary aerosols.
Furthermore, we investigated the influence of transition metals like copper and
iron on the OP of secondary organic aerosol. We could show that there is a
synergistic effect for biogenic SOA with copper and for anthropogenic SOA with
copper and iron, but an antagonistic effect with iron and biogenic SOA measured
with the OOPAAI.