4 research outputs found
Oxidative Potential of Atmospheric Particles at an Eastern Mediterranean Site
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)
Sources of water-soluble Brown Carbon at a South-Eastern European Site
Atmospheric brown carbon (BrC) is a highly uncertain, but potentially important contributor to light absorption in the atmosphere. Laboratory and field studies have shown that BrC can be produced from multiple sources, including primary emissions from fossil fuel combustion and biomass burning (BB), as well as secondary formation through a number of reaction pathways. It is currently thought that the dominant source of atmospheric BrC is primary emissions from BB, but relatively few studies demonstrate this in environments with complex source profiles.
A field campaign was conducted during a month-long wintertime period in 2020 on the campus of the University of Peloponnese in the southwest of Patras, Greece which represents an urban site. During this time, ambient filter samples (a total of 35 filters) were collected from which the water-soluble BrC was determined using a semi-automated system similar to Hecobian et al. (2010), where absorption was measured over a 1 m path length. To measure the BrC, a UV-Vis Spectrophotometer was coupled to a Liquid Waveguide Capillary Cell and the light absorption intensity was recorded at 365 and 700 nm. The latter was used as a reference wavelength. We found that the average BrC absorption in Patras at a wavelength of 365 nm was 8.5 ± 3.9 Mm-1 suggesting that there was significant BrC in the organic aerosol during this period. Attribution of sources of BrC was done using simultaneous chemical composition data observations (primarily organic carbon, black carbon, and nitrate) combined with Positive Matrix Factorization analysis. This analysis showed that in addition to the important role of biomass burning (a contribution of about 20%) and other combustion emissions (also close to 20%), oxidized organic aerosol (approximately 40%) is also a significant contributor to BrC in the study area.
Reference
Hecobian, A., Zhang, X., Zheng, M., Frank, N., Edgerton, E.S., Weber, R.J., 2010. Water-soluble organic aerosol material and the light-absorption characteristics of aqueous extracts measured over the Southeastern United States. Atmos. Chem. Phys. 10, 5965–5977. https://doi.org/10.5194/acp-10-5965-201
Significant spatial gradients in new particle formation frequency in Greece during summer
Extensive continuous particle number size distribution measurements took place during two summers (2020 and 2021) at 11 sites in Greece for the investigation of the frequency and the spatial extent of new particle formation (NPF). The study area is characterized by high solar intensity and fast photochemistry and has moderate to low fine particulate matter levels during the summer. The average PM2.5 levels were relatively uniform across the examined sites. The NPF frequency during summer varied from close to zero in the southwestern parts of Greece to more than 60 % in the northern, central, and eastern regions. The mean particle growth rate for each station varied between 3.4 and 8 nm h−1, with an average rate of 5.7 nm h−1. At most of the sites there was no statistical difference in the condensation sink between NPF event and non-event days, while lower relative humidity was observed during the events. The high-NPF-frequency sites in the north and northeast were in close proximity to both coal-fired power plants (high emissions of SO2) and agricultural areas with some of the highest ammonia emissions in the country. The southern and western parts of Greece, where NPF was infrequent, were characterized by low ammonia emissions, while moderate levels of sulfuric acid were estimated (107 molec. cm−3) in the west. Although the emissions of biogenic volatile organic compounds were higher in western and southern sectors, they did not appear to lead to enhanced frequency of NPF. The infrequent events at these sites occurred when the air masses had spent a few hours over areas with agricultural activities and thus elevated ammonia emissions. Air masses arriving at the sites directly from the sea were not connected with atmospheric NPF. These results support the hypothesis that ammonia and/or amines limit new particle formation in the study area.</p
Gas and Particulate Pollution in Patras (Greece) during PANACEA 2019 – 2020
Extensive aerosol measurements were conducted in Patras (Greece) within the framework of the PANACEA summer and winter campaigns in Greece. During both periods a high-resolution time-of-flight aerosol mass spectrometer coupled with a variety of other instruments were deployed for measuring the chemical composition and concentration of fine particulate matter. The data are complemented with carbon monoxide, ozone, sulfur dioxide, and nitrogen oxides measurements. Volatile organic compounds concentrations were measured by a proton transfer-reaction mass spectrometer during part of the winter campaign. PM2.5 measurements from a network of fifteen low-cost sensors are also available. The aim of the campaigns was to enhance our knowledge of particulate air pollution and the resulting human exposure in major Greek cities. During the summer, positive matrix factorization showed that 90% of the OA was secondary and quite oxidized, while in winter biomass burning for residential heating was the dominant source of particulate matter