Aerosol oxidative potential (OP; the inherent ability of
ambient particles to generate reactive oxygen species in
vivo) may be linked to the health effects of population
exposure to aerosol and is a metric of their toxicity. The
goal of this work was to quantify the water-soluble OP of
particles in an urban area in Patras, Greece and to
investigate its links with source emissions or components
of this particulate matter (PM).
A field campaign was conducted during a monthlong
wintertime period in 2020 (January 10 to February
13) on the campus of the University of Peloponnese in
the southwest of Patras. During this time, ambient filter
samples (a total of 35 filters) were collected.
To measure the water-soluble OP we used a semiautomated
system similar to Fang et al. (2015) based on
the dithiothreitol (DTT) assay. The accuracy of our system
was validated by measuring the DTT activity of 11
phenanthrequinone (PQN) solutions on both our system
and the identical semi-automated validated system at
the National Observatory of Athens (NOA). These two
sets of analysed DTT activities (current vs. NOA system)
were significantly correlated (R2=0.99) with a slope of
1.15 ± 0.04 and an intercept close to zero.
We found that the average water-soluble OP in
Patras was 1.5 ± 0.3 nmol min-1 m-3, ranging from 0.7 to
2 nmol min-1 m-3. The OP measured in Patras during the
campaign is higher than reported values from similar
wintertime studies in other urban areas such as Athens
(Paraskevopoulou et al., 2019). The average watersoluble
OP during a summer study for Patras was
significantly lower and equal to 0.18 ± 0.02 nmol min-1 m-
3. Taking into account the average PM1 mass
concentrations for these two periods (summer: 6 μg m-3
and winter: 23 μg m-3) it is clear that the increase in OP
was two times the increase in PM mass making the
wintertime aerosol more toxic.
Additionally, the water-soluble brown carbon
(BrC) was determined using an offline semi-automated
system, where absorption was measured over a 1 m path
length. The average BrC absorption in Patras at a
wavelength of 365 nm was 8.6 ± 3.9 Mm-1 suggesting that
there was significant BrC in the organic aerosol during
this period.
The coefficients of determination, R2, in Table 1
are used as a metric of the potential relationships
between the various carbonaceous aerosol components
and the DTT activity. The results suggest that the OP is
not dominated by a single source or component, but that
there are multiple components contributing to it during
the study period.
Interestingly, the highest correlation coefficient
(R2 = 0.46) was found between the OP and Brown Carbon.
This is consistent with recently published results for an
urban site in Atlanta where the oxidative potential
measured with the DTT method also had stronger
correlations with BrC during the winter (Gao et al., 2020)