45 research outputs found
A portable dual-smog-chamber system for atmospheric aerosol field studies
Smog chamber experiments using ambient air as a starting point can improve
our understanding of the evolution of atmospheric particulate matter at
timescales longer than those achieved by traditional laboratory experiments.
These types of studies can take place under more realistic environmental
conditions addressing the interactions among multiple pollutants. The use of
two identical smog chambers, with the first serving as the baseline chamber
and the second as the perturbation chamber (in which addition or removal of
pollutants, addition of oxidants, change in the relative humidity, etc.),
can facilitate the interpretation of the results in such inherently complex
experiments. The differences of the measurements in the two chambers can be
used as the basis for the analysis of the corresponding chemical or physical
processes of ambient air.
A portable dual-smog-chamber system was developed using two identical
pillow-shaped smog chambers (1.5 m3 each). The two chambers are
surrounded by UV lamps in a hexagonal arrangement yielding a total
JNO2 of 0.1 min−1. The system can be easily disassembled and
transported, enabling the study of various atmospheric environments.
Moreover, it can be used with natural sunlight. The results of test
experiments using ambient air as the starting point are discussed as examples of
applications of this system.</p
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
Rapid dark aging of biomass burning as an overlooked source of oxidized organic aerosol
To quantify the full implications of biomass burning emissions on the atmosphere, it is essential to accurately represent the emission plume after it has undergone chemical aging in the atmosphere. Atmospheric models typically consider the predominant aging pathway of biomass burning emissions to take place in the presence of sunlight (via the OH radical); however, this mechanism leads to consistent underpredictions of oxidized organic aerosol in wintertime urban areas. Here, we show, through a combination of laboratory experiments, ambient field measurements, and chemical transport modeling, that biomass burning emission plumes exposed to NO2 and O3 age rapidly without requiring any sunlight, thus providing an overlooked source of oxidized organic aerosol previously not accounted for in models
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)
Chemical evolution of primary and secondary biomass burning aerosols during daytime and nighttime
Primary emissions from wood and pellet stoves were aged in an atmospheric simulation chamber under daytime and nighttime conditions. The aerosol was analyzed with the online Aerosol Mass Spectrometer (AMS) and offline Fourier transform infrared spectroscopy (FTIR). Measurements using the two techniques agreed reasonably well in terms of the organic aerosol (OA) mass concentration, OA:OC trends, and concentrations of biomass burning markers – lignin-like compounds and anhydrosugars. Based on the AMS, around 15 % of the primary organic aerosol (POA) mass underwent some form of transformation during daytime oxidation conditions after 6–10 hours of atmospheric exposure. A lesser extent of transformation was observed during the nighttime oxidation. The decay of certain semi-volatile (e.g., levoglucosan) and less volatile (e.g., lignin-like) POA components was substantial during aging, highlighting the role of heterogeneous reactions and gas-particle partitioning. Lignin-like compounds were observed to degrade under both daytime and nighttime conditions, whereas anhydrosugars degraded only under daytime conditions. Among the marker mass fragments of primary biomass burning OA (bbPOA), heavy ones (higher m/z) were relatively more stable during aging. The biomass burning secondary OA (bbSOA) became more oxidized with continued aging and resembled those of aged atmospheric organic aerosols. The bbSOA formed during daytime oxidation was dominated by acids. Organonitrates were an important product of nighttime reactions in both humid and dry conditions. Our results underline the importance of changes to both the primary and secondary biomass burning aerosols during their atmospheric aging. Heavier AMS fragments seldomly used in atmospheric chemistry can be used as more stable tracers of bbPOA and in combination with the established levoglucosan marker, can provide an indication of the extent of bbPOA aging
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
TNFR1 inhibition with a nanobody protects against EAE development in mice
TNF has as detrimental role in multiple sclerosis (MS), however, anti-TNF medication is not working. Selective TNF/TNFR1 inhibition whilst sparing TNFR2 signaling reduces the pro-inflammatory effects of TNF but preserves the important neuroprotective signals via TNFR2. We previously reported the generation of a Nanobody-based selective inhibitor of human TNFR1, TROS that will be tested in experimental autoimmune encephalomyelitis (EAE). We specifically antagonized TNF/TNFR1 signaling using TROS in a murine model of MS, namely MOG(35-55)-induced EAE. Because TROS does not cross-react with mouse TNFR1, we generated mice expressing human TNFR1 in a mouse TNFR1-knockout background (hTNFR1 Tg), and we determined biodistribution of Tc-99m-TROS and effectiveness of TROS in EAE in those mice. Biodistribution analysis demonstrated that intraperitoneally injected TROS is retained more in organs of hTNFR1 Tg mice compared to wild type mice. TROS was also detected in the cerebrospinal fluid (CSF) of hTNFR1 Tg mice. Prophylactic TROS administration significantly delayed disease onset and ameliorated its symptoms. Moreover, treatment initiated early after disease onset prevented further disease development. TROS reduced spinal cord inflammation and neuroinflammation, and preserved myelin and neurons. Collectively, our data illustrate that TNFR1 is a promising therapeutic target in MS
Estimation of the volatility distribution of organic aerosol combining thermodenuder and isothermal dilution measurements
A method is developed following the work of Grieshop et al. (2009) for the
determination of the organic aerosol (OA) volatility distribution combining
thermodenuder (TD) and isothermal dilution measurements. The approach was tested
in experiments that were conducted in a smog chamber using organic aerosol
(OA) produced during meat charbroiling. A TD was operated at
temperatures ranging from 25 to 250 °C with a 14 s centerline residence
time coupled to a high-resolution time-of-flight aerosol mass spectrometer
(HR-ToF-AMS) and a scanning mobility particle sizer (SMPS). In parallel, a
dilution chamber filled with clean air was used to dilute isothermally the
aerosol of the larger chamber by approximately a factor of 10. The OA mass
fraction remaining was measured as a function of temperature in the TD and
as a function of time in the isothermal dilution chamber. These two sets of
measurements were used together to estimate the volatility distribution of
the OA and its effective vaporization enthalpy and accommodation
coefficient. In the isothermal dilution experiments approximately 20 % of
the OA evaporated within 15 min. Almost all the OA evaporated in the TD at
approximately 200 °C. The resulting volatility distributions suggested
that around 60–75 % of the cooking OA (COA) at concentrations around
500 µg m−3 consisted of low-volatility organic compounds (LVOCs),
20–30 % of semivolatile organic compounds (SVOCs), and around 10 % of
intermediate-volatility organic compounds (IVOCs). The estimated effective
vaporization enthalpy of COA was 100 ± 20 kJ mol−1 and the
effective accommodation coefficient was 0.06–0.07. Addition of the dilution
measurements to the TD data results in a lower uncertainty of the estimated
vaporization enthalpy as well as the SVOC content of the OA
Hygroscopic properties of atmospheric particles emitted during wintertime biomass burning episodes in Athens
This study explores the Cloud Condensation Nuclei (CCN) activity of atmospheric particles during intense biomass burning periods in an urban environment. During a one-month campaign in the center of Athens, Greece, a CCN counter coupled with a Scanning Mobility Particle Sizer (SMPS) and a high resolution Aerosol Mass Spectrometer (HR-AMS) were used to measure the size-resolved CCN activity and composition of the atmospheric aerosols. During the day, the organic fraction of the particles was more than 50%, reaching almost 80% at night, when the fireplaces were used. Positive Matrix Factorization (PMF) analysis revealed 4 factors with biomass burning being the dominant source after 18:00 until the early morning. The CCN-based overall hygroscopicity parameter κ ranged from 0.15 to 0.25. During the night, when the biomass burning organic aerosol (bbOA) dominated, the hygroscopicity parameter for the mixed organic/inorganic particles was on average 0.16. The hygroscopicity of the biomass-burning organic particles was 0.09, while the corresponding average value for all organic particulate matter during the campaign was 0.12. © 2018 Elsevier Lt