444 research outputs found
Single-particle characterization of the high-Arctic summertime aerosol
Single-particle mass-spectrometric measurements were carried out in
the high Arctic north of 80° during summer 2008. The
campaign took place onboard the icebreaker <i>Oden</i> and was
part of the Arctic Summer Cloud Ocean Study (ASCOS). The instrument
deployed was an aerosol time-of-flight mass spectrometer (ATOFMS)
that provides information on the chemical composition of individual
particles and their mixing state in real time. Aerosols were sampled
in the marine boundary layer at stations in the open ocean, in the
marginal ice zone, and in the pack ice region. The largest fraction
of particles detected for subsequent analysis in the size range of
the ATOFMS between approximately 200 and 3000 nm in diameter
showed mass-spectrometric patterns, indicating an internal mixing
state and a biomass burning and/or biofuel source. The majority of
these particles were connected to an air mass layer of elevated
particle concentration mixed into the surface mixed layer from the
upper part of the marine boundary layer. The second largest fraction
was represented by sea salt particles. The chemical analysis of the
over-ice sea salt aerosol revealed tracer compounds that reflect
chemical aging of the particles during their long-range advection
from the marginal ice zone, or open waters south thereof prior to
detection at the ship. From our findings we conclude that long-range
transport of particles is one source of aerosols in the high
Arctic. To assess the importance of long-range particle sources for
aerosol–cloud interactions over the inner Arctic in comparison to
local and regional biogenic primary aerosol sources, the chemical
composition of the detected particles was analyzed for indicators of
marine biological origin. Only a minor fraction showed chemical
signatures of potentially ocean-derived primary particles of that
kind. However, a chemical bias in the ATOFMS's detection
capabilities observed during ASCOS might suggest the presence of
a particle type of unknown composition and source. In general, the
study suffered from low counting statistics due to the overall small
number of particles found in this pristine environment, the small
sizes of the prevailing aerosol below the detection limit of the
ATOFMS, and its low hit rate. To our knowledge, this study reports on
the first in situ single-particle mass-spectrometric measurements in
the marine boundary layer of the high-Arctic pack ice region
Changes in aerosol properties during spring-summer period in the Arctic troposphere
The change in aerosol properties during the transition from the more polluted spring to the clean summer in the Arctic troposphere was studied. A six-year data set of observations from Ny-Ă…lesund on Svalbard, covering the months April through June, serve as the basis for the characterisation of this time period. In addition four-day-back trajectories were used to describe air mass histories. The observed transition in aerosol properties from an accumulation-mode dominated distribution to an Aitken-mode dominated distribution is discussed with respect to long-range transport and influences from natural and anthropogenic sources of aerosols and pertinent trace gases. Our study shows that the air-mass transport is an important factor modulating the physical and chemical properties observed. However, the air-mass transport cannot alone explain the annually repeated systematic and rather rapid change in aerosol properties, occurring within a limited time window of approximately 10 days. With a simplified phenomenological model, which delivers the nucleation potential for new-particle formation, we suggest that the rapid shift in aerosol microphysical properties between the Arctic spring and summer is mainly driven by the incoming solar radiation in concert with transport of precursor gases and changes in condensational sink
Decreased carbon accumulation feedback driven by climate-induced drying of two southern boreal bogs over recent centuries
Northern boreal peatlands are important ecosystems in modulating global biogeochemical cycles, yet their biological communities and related carbon dynamics are highly sensitive to changes in climate. Despite this, the strength and recent direction of these feedbacks are still unclear. The response of boreal peatlands to climate warming has received relatively little attention compared with other northern peatland types, despite forming a large northern hemisphere-wide ecosystem. Here, we studied the response of two ombrotrophic boreal peatlands to climate variability over the last c. 200 years for which local meteorological data are available. We used remains from plants and testate amoebae to study historical changes in peatland biological communities. These data were supplemented by peat property (bulk density, carbon and nitrogen content), C-14, Pb-210 and Cs-137 analyses and were used to infer changes in peatland hydrology and carbon dynamics. In total, six peat cores, three per study site, were studied that represent different microhabitats: low hummock (LH), high lawn and low lawn. The data show a consistent drying trend over recent centuries, represented mainly as a change from wet habitat Sphagnum spp. to dry habitat S. fuscum. Summer temperature and precipitation appeared to be important drivers shaping peatland community and surface moisture conditions. Data from the driest microhabitat studied, LH, revealed a clear and strong negative linear correlation (R-2 = .5031; p <.001) between carbon accumulation rate and peat surface moisture conditions: under dry conditions, less carbon was accumulated. This suggests that at the dry end of the moisture gradient, availability of water regulates carbon accumulation. It can be further linked to the decreased abundance of mixotrophic testate amoebae under drier conditions (R-2 = .4207; p <.001). Our study implies that if effective precipitation decreases in the future, the carbon uptake capacity of boreal bogs may be threatened.Peer reviewe
Ion production rate in a boreal forest based on ion, particle and radiation measurements
International audienceIn this study the ion production rates in a boreal forest were studied based on two different methods: 1) cluster ion and particle concentration measurements, 2) external radiation and radon concentration measurements. Both methods produced reasonable estimates for ion production rates. The average ion production rate calculated from aerosol particle size distribution and air ion mobility distribution measurements was 2.6 ion pairs cm-3s-1, and based on external radiation and radon measurements, 4.5 ion pairs cm-3s-1. The first method based on ion and particle measurements gave lower values for the ion production rates especially during the day. A possible reason for this is that particle measurements started only from 3nm, so the sink of small ions during the nucleation events was underestimated. It may also be possible that the hygroscopic growth factors of aerosol particles were underestimated. Another reason for the discrepancy is the nucleation mechanism itself. If the ions are somehow present in the nucleation process, there could have been an additional ion sink during the nucleation days
Categorical Dimensions of Human Odor Descriptor Space Revealed by Non-Negative Matrix Factorization
In contrast to most other sensory modalities, the basic perceptual dimensions of olfaction remain unclear. Here, we use non-negative matrix factorization (NMF) – a dimensionality reduction technique – to uncover structure in a panel of odor profiles, with each odor defined as a point in multi-dimensional descriptor space. The properties of NMF are favorable for the analysis of such lexical and perceptual data, and lead to a high-dimensional account of odor space. We further provide evidence that odor dimensions apply categorically. That is, odor space is not occupied homogenously, but rather in a discrete and intrinsically clustered manner. We discuss the potential implications of these results for the neural coding of odors, as well as for developing classifiers on larger datasets that may be useful for predicting perceptual qualities from chemical structures
Lymphatic endothelium stimulates melanoma metastasis and invasion via MMP14-dependent Notch3 and b1-integrin activation
Lymphatic invasion and lymph node metastasis correlate with poor clinical outcome in melanoma. However, the mechanisms of lymphatic dissemination in distant metastasis remain incompletely understood. We show here that exposure of expansively growing human WM852 melanoma cells, but not singly invasive Bowes cells, to lymphatic endothelial cells (LEC) in 3D co-culture facilitates melanoma distant organ metastasis in mice. To dissect the underlying molecular mechanisms, we established LEC co-cultures with different melanoma cells originating from primary tumors or metastases. Notably, the expansively growing metastatic melanoma cells adopted an invasively sprouting phenotype in 3D matrix that was dependent on MMP14, Notch3 and β1-integrin. Unexpectedly, MMP14 was necessary for LEC-induced Notch3 induction and coincident β1-integrin activation. Moreover, MMP14 and Notch3 were required for LEC-mediated metastasis of zebrafish xenografts. This study uncovers a unique mechanism whereby LEC contact promotes melanoma metastasis by inducing a reversible switch from 3D growth to invasively sprouting cell phenotype
Chemical composition of boundary layer aerosol over the Atlantic Ocean and at an Antarctic site
International audienceAerosol chemical composition was measured over the Atlantic Ocean in November?December 1999 and at the Finnish Antarctic research station Aboa in January 2000. The concentrations of all anthropogenic aerosol compounds decreased clearly from north to south. An anthropogenic influence was still evident in the middle of the tropical South Atlantic, background values were reached south of Cape Town. Chemical mass balance was calculated for high volume filter samples (Dp80% in the Southern Ocean, and 10% in most samples, also at Aboa. The correlation of biomass-burning-related aerosol components with 210Pb was very high compared with that between nss calcium and 210Pb which suggests that 210Pb is a better tracer for biomass burning than for Saharan dust. The ratio of the two clear tracers for biomass burning, nss potassium and oxalate, was different in European and in African samples, suggesting that this ratio could be used as an indicator of biomass burning type. The concentrations of continent-related particles decreased exponentially with the distance from Africa. The shortest half-value distance, ~100 km, was for nss calcium. The half-value distance of particles that are mainly in the submicron particles was ~700±200 km. The MSA to nss sulfate ratio, R, increased faster than MSA concentration with decreasing anthropogenic influence, indicating that the R increase could largely be explained by the decrease of anthropogenic sulfate
Receptor modeling of near-roadway aerosol mass spectrometer data in Las Vegas, Nevada, with EPA PMF
Ambient non-refractory PM<sub>1</sub> aerosol particles were measured with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-AMS) at an elementary school 18 m from the US 95 freeway soundwall in Las Vegas, Nevada, during January 2008. Additional collocated continuous measurements of black carbon (BC), carbon monoxide (CO), nitrogen oxides (NO<sub>x</sub>), and meteorological data were collected. The US~Environmental Protection Agency's (EPA) positive matrix factorization (PMF) data analysis tool was used to apportion organic matter (OM) as measured by HR-AMS, and rotational tools in EPA PMF were used to better characterize the solution space and pull resolved factors toward known source profiles. Three- to six-factor solutions were resolved. The four-factor solution was the most interpretable, with the typical AMS PMF factors of hydrocarbon-like organic aerosol (HOA), low-volatility oxygenated organic aerosol (LV-OOA), biomass burning organic aerosol (BBOA), and semi-volatile oxygenated organic aerosol (SV-OOA). When the measurement site was downwind of the freeway, HOA composed about half the OM, with SV-OOA and LV-OOA accounting for the rest. Attempts to pull the PMF factor profiles toward source profiles were successful but did not qualitatively change the results, indicating that these factors are very stable. Oblique edges were present in G-space plots, suggesting that the obtained rotation may not be the most plausible one. Since solutions found by pulling the profiles or using <i>F</i><sub>peak</sub> retained these oblique edges, there appears to be little rotational freedom in the base solution. On average, HOA made up 26% of the OM, while LV-OOA was highest in the afternoon and accounted for 26% of the OM. BBOA occurred in the evening hours, was predominantly from the residential area to the north, and on average constituted 12% of the OM; SV-OOA accounted for the remaining third of the OM. Use of the pulling techniques available in EPA PMF and ME-2 suggested that the four-factor solution was very stable
Wide Spread Exploitations of Bioenergy: Are the Ways towards Sustainable Energy?
Abstract-The recoverable proven reserves of fossil fuel sources are projected to be exhausted by the end of this century. In response to the exhaustion of fossil resources, there is a serious need to find alternative fuel sources. Bioenergy is one of the potential candidates to counteract the fossil-fuel depletion challenge. Despite bioenergy sources appear to be renewable and net-zero GHG emitting, bioenergy undergoes competition with food, feed and other crucial applications. Since earth's eco system has a limited capacity of land and water resources, overuse of these resources in bioenergy production could cause adverse social and environmental impacts. This paper summarizes the key sustainability issues involve in bioenergy chain, and examine the potential role of bioenergy in dealing with these sustainability issues. We found that bioenergy can be a sustainable source of energy provided that it has maintained irrationality is using of natural resources and several limits. In contrary, bioenergy would provoke further social and environmental problems if the sustainability issues are not given proper consideration
The Effects of Particulate Matter Sources on Daily Mortality: A Case-Crossover Study of Barcelona, Spain
Background: Dozens of studies link acute exposure to particulate matter (PM) air pollution with premature mortality and morbidity, but questions remain about which species and sources in the vast PM mixture are responsible for the observed health effects. Although a few studies exist on the effects of species and sources in U.S. cities, European cities—which have a higher proportion of diesel engines and denser urban populations—have not been well characterized. Information on the effects of specific sources could aid in targeting pollution control and in articulating the biological mechanisms of PM
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