258 research outputs found
Source apportionment of PM<sub>2.5</sub> in Cork Harbour, Ireland using a combination of single particle mass spectrometry and quantitative semi-continuous measurements
An aerosol time-of-flight mass spectrometer (ATOFMS) was deployed for the measurement of the size resolved chemical composition of single particles at a site in Cork Harbour, Ireland for three weeks in August 2008. The ATOFMS was co-located with a suite of semi-continuous instrumentation for the measurement of particle number, elemental carbon (EC), organic carbon (OC), sulfate and particulate matter smaller than 2.5 ÎŒm in diameter (PM<sub>2.5</sub>). The temporality of the ambient ATOFMS particle classes was subsequently used in conjunction with the semi-continuous measurements to apportion PM<sub>2.5</sub> mass using positive matrix factorisation. The synergy of the single particle classification procedure and positive matrix factorisation allowed for the identification of six factors, corresponding to vehicular traffic, marine, long-range transport, various combustion, domestic solid fuel combustion and shipping traffic with estimated contributions to the measured PM<sub>2.5</sub> mass of 23%, 14%, 13%, 11%, 5% and 1.5% respectively. Shipping traffic was found to contribute 18% of the measured particle number (20â600 nm mobility diameter), and thus may have important implications for human health considering the size and composition of ship exhaust particles. The positive matrix factorisation procedure enabled a more refined interpretation of the single particle results by providing source contributions to PM<sub>2.5</sub> mass, while the single particle data enabled the identification of additional factors not possible with typical semi-continuous measurements, including local shipping traffic
Mixotrophic uptake of organic compounds by coccolithophores
Osmotrophy is one of the main modes of mixotrophic acquisition of carbon by phytoplankton, but historically it has been underâinvestigated and its physiological and ecological relevance remains poorly understood. Here, we investigate osmotrophy in coccolithophores. Coccolithophores are one of the major contributors to the ocean biomass inhabiting both euphotic and subeuphotic depths in the marine environment. Coccolithophores demonstrate the potential to utilize a wide array of organic compounds in darkness. In experiments with BioLog Ecoplates, we screened a wide array of organic compounds as potential carbon sources, and observed that the major types of organic compounds taken up by coccolithophores were primarily carbohydrates along with a few amino acids and polymers. Furthermore, in subsequent radiotracer experiments, the uptake rates of 14Câlabeled dissolved organic carbon compounds in the dark were low relative to the maximal rates of photosynthetic carbon fixation in the light. The time course of uptake for some compounds suggests constitutive capacity for their transport, while for others the transport appears to be activated. Nonetheless, the collective slow uptake rate of a large array of organic compounds found in seawater, might be the only way that osmotrophy could fuel significant coccolithophore growth in the deep euphotic and subeuphotic zones in the sea
Investigation of coastal sea-fog formation using the WIBS (wideband integrated bioaerosol sensor) technique
A wideband integrated bioaerosol sensor (WIBS-4) was deployed in
Haulbowline Island, Cork Harbour, to detect fluorescence particles in
real time during July and September 2011. A scanning mobility particle sizer
(SMPS) was also installed providing sizing analysis of the particles over the
10â450 nm range. During the campaign, multiple fog formation events
occurred; they coincided with dramatic increases in the recorded fluorescent
particle counts. The WIBS sizing and fluorescence intensity profiles indicated
that the origin of the signals was potentially non-biological in nature (i.e.
PBAPs, primary biological aerosol particles). Furthermore, the data did not
support the presence of known fluorescing chemical particles like SOA
(secondary organic aerosol). Complementary laboratory studies showed that the
field results could potentially be explained by the adsorption of molecular
iodine onto water droplets to form
I2 â
 (H2O)x complexes. The release of
iodine into the coastal atmosphere from exposed kelp at low tides has been
known for many years. This process leads to the production of small
IxOy particles, which can act as cloud condensation
nuclei (CCN). While the process of molecular iodine release from coastal kelp
sources, subsequent particle formation, and the observations of sea mists and
fogs have been studied in detail, this study provides a potential link
between the three phenomena. Of mechanistic interest is the fact that
molecular iodine included into (rather than on) water droplets does not
appear to fluoresce as measured using WIBS instrumentation. The study
indicates a previously unsuspected stabilizing transport mechanism for iodine
in the marine environment. Hence the stabilization of the molecular form
would allow its more extensive distribution throughout the troposphere before
eventual photolysis.</p
Precision of the current methods to measure the alkenone proxy UK'37 and absolute alkenone abundance in sediments : results of an interlaboratory comparison study
Measurements of the UK'37 index and the absolute abundance of alkenones in marine sediments are increasingly used in paleoceanographic research as proxies of past sea surface temperature and haptophyte (mainly coccolith-bearing species) primary productivity, respectively. An important aspect of these studies is to be able to compare reliably data obtained by different laboratories from a wide variety of locations. Hence the intercomparability of data produced by the research community is essential. Here we report results from an anonymous interlaboratory comparison study involving 24 of the leading laboratories that carry out alkenone measurements worldwide. The majority of laboratories produce data that are intercomparable within the considered confidence limits. For the measurement of alkenone concentrations, however, there are systematic biases between laboratories, which might be related to the techniques employed to quantify the components. The maximum difference between any two laboratories for any two single measurements of UK'37 in sediments is estimated, with a probability of 95%, to be <2.18C. In addition, the overall within-laboratory precision for the UK'37 temperature estimates is estimated to be <1.68C (95% probability). Similarly, from the analyses of alkenone concentrations the interlaboratory reproducibility is estimated at 32%, and the repeatability is estimated at 24%. The former is compared to a theoretical estimate of reproducibility and found to be excessively high. Hence there is certainly scope and a demonstrable need to improve reproducibility and repeatability of UK'37 and especially alkenone quantification data across the community of scientists involved in alkenone research
A new methodology to assess the performance and uncertainty of source apportionment models II: The results of two European intercomparison exercises
The performance and the uncertainty of receptor models (RMs) were assessed in intercomparison exercises employing real-world and synthetic input datasets. To that end, the results obtained by different practitioners using ten different RMs were compared with a reference. In order to explain the differences in the performances and uncertainties of the different approaches, the apportioned mass, the number of sources, the chemical profiles, the contribution-to-species and the time trends of the sources were all evaluated using the methodology described in Belis et al. (2015). In this study, 87% of the 344 source contribution estimates (SCEs) reported by participants in 47 different source apportionment model results met the 50% standard uncertainty quality objective established for the performance test. In addition, 68% of the SCE uncertainties reported in the results were coherent with the analytical uncertainties in the input data. The most used models, EPA-PMF v.3, PMF2 and EPA-CMB 8.2, presented quite satisfactory performances in the estimation of SCEs while unconstrained models, that do not account for the uncertainty in the input data (e.g. APCS and FA-MLRA), showed below average performance. Sources with well-defined chemical profiles and seasonal time trends, that make appreciable contributions (>10%), were those better quantified by the models while those with contributions to the PM mass close to 1% represented a challenge. The results of the assessment indicate that RMs are capable of estimating the contribution of the major pollution source categories over a given time window with a level of accuracy that is in line with the needs of air quality management
Evaluation of receptor and chemical transport models for PM10 source apportionment
In this study, the performance of two types of source apportionment models was evaluated by assessing the results provided by 40 different groups in the framework of an intercomparison organised by FAIRMODE WG3 (Forum for air quality modelling in Europe, Working Group 3). The evaluation was based on two performance indicators: z-scores and the root mean square error weighted by the reference uncertainty (RMSEu), with pre-established acceptability criteria. By involving models based on completely different and independent input data, such as receptor models (RMs) and chemical transport models (CTMs), the intercomparison provided a unique opportunity for their cross-validation. In addition, comparing the CTM chemical profiles with those measured directly at the source contributed to corroborate the consistency of the tested model results. The most commonly used RM was the US EPA- PMF version 5. RMs showed very good performance for the overall dataset (91% of z-scores accepted) while more difficulties were observed with the source contribution time series (72% of RMSEu accepted). Industrial activities proved to be the most difficult sources to be quantified by RMs, with high variability in the estimated contributions. In the CTMs, the sum of computed source contributions was lower than the measured gravimetric PM10 mass concentrations. The performance tests pointed out the differences between the two CTM approaches used for source apportionment in this study: brute force (or emission reduction impact) and tagged species methods. The sources meeting the z-score and RMSEu acceptability criteria tests were 50% and 86%, respectively. The CTM source contributions to PM10 were in the majority of cases lower than the RM averages for the corresponding source. The CTMs and RMs source contributions for the overall dataset were more comparable (83% of the z-scores accepted) than their time series (successful RMSEu in the range 25% - 34%). The comparability between CTMs and RMs varied depending on the source: traffic/exhaust and industry were the source categories with the best results in the RMSEu tests while the most critical ones were soil dust and road dust. The differences between RMs and CTMs source reconstructions confirmed the importance of cross validating the results of these two families of models
Short-course PET based simultaneous integrated boost for locally advanced cervical cancer
Results of the first European Source Apportionment intercomparison for Receptor and Chemical Transport Models
In this study, the performance of the source apportionment model applications were evaluated by comparing the model results provided by 44 participants adopting a methodology based on performance indicators: z-scores and RMSEu, with pre-established acceptability criteria. Involving models based on completely different and independent input data, such as receptor models (RMs) and chemical transport models (CTMs), provided a unique opportunity to cross-validate them. In addition, comparing the modelled source chemical profiles, with those measured directly at the source contributed to corroborate the chemical profile of the tested model results. The most used RM was EPA- PMF5. RMs showed very good performance for the overall dataset (91% of z-scores accepted) and more difficulties are observed with SCE time series (72% of RMSEu accepted). Industry resulted the most problematic source for RMs due to the high variability among participants. Also the results obtained with CTMs were quite comparable to their ensemble reference using all models for the overall average (>92% of successful z-scores) while the comparability of the time series is more problematic (between 58% and 77% of the candidatesâ RMSEu are accepted). In the CTM models a gap was observed between the sum of source contributions and the gravimetric PM10 mass likely due to PM underestimation in the base case. Interestingly, when only the tagged species CTM results were used in the reference, the differences between the two CTM approaches (brute force and tagged species) were evident. In this case the percentage of candidates passing the z-score and RMSEu tests were only 50% and 86%, respectively. CTMs showed good comparability with RMs for the overall dataset (83% of the z-scores accepted), more differences were observed when dealing with the time series of the single source categories. In this case the share of successful RMSEu was in the range 25% - 34%.JRC.C.5-Air and Climat
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Precision of the current methods to measure the alkenone proxy Uââ Kâ and absolute alkenone abundance in sediments: results of an interlaboratory comparison study
Measurements of the Uââ Kâ index and the absolute abundance of alkenones in marine sediments are increasingly used in paleoceanographic research as proxies of past sea surface
temperature and haptophyte (mainly coccolith-bearing species) primary productivity, respectively. An
important aspect of these studies is to be able to compare reliably data obtained by different laboratories
from a wide variety of locations. Hence the intercomparability of data produced by the research
community is essential. Here we report results from an anonymous interlaboratory comparison study
involving 24 of the leading laboratories that carry out alkenone measurements worldwide. The majority
of laboratories produce data that are intercomparable within the considered confidence limits. For the measurement of alkenone concentrations, however, there are systematic biases between laboratories,
which might be related to the techniques employed to quantify the components. The maximum
difference between any two laboratories for any two single measurements of Uââ Kâ in sediments is
estimated, with a probability of 95%, to be <2.1°C. In addition, the overall within-laboratory precision
for the Uââ Kâ temperature estimates is estimated to be <1.6°C (95% probability). Similarly, from the
analyses of alkenone concentrations the interlaboratory reproducibility is estimated at 32%, and the
repeatability is estimated at 24%. The former is compared to a theoretical estimate of reproducibility
and found to be excessively high. Hence there is certainly scope and a demonstrable need to improve
reproducibility and repeatability of Uââ Kâ and especially alkenone quantification data across the
community of scientists involved in alkenone research
Living on Cold Substrata: New Insights and Approaches in the Study of Microphytobenthos Ecophysiology and Ecology in Kongsfjorden
Organisms in shallow waters at high latitudes are under pressure due to climate change. These areas are typically inhabited by microphytobenthos (MPB) communities, composed mainly of diatoms. Only sparse information is available on the ecophysiology and acclimation processes within MPBs from Arctic regions. The
physico-chemical environment and the ecology and ecophysiology of benthic diatoms in Kongsfjorden (Svalbard, Norway) are addressed in this review. MPB biofilms cover extensive areas of sediment. They show high rates of primary production, stabilise sediment surfaces against erosion under hydrodynamic forces,and affect the exchange of oxygen and nutrients across the sediment-water interface. Additionally, this phototrophic community represents a key component in the functioning of the Kongsfjorden trophic web, particularly as a major food source for benthic suspension- or deposit-feeders. MPB in Kongsfjorden is confronted with pronounced seasonal variations in solar radiation, low temperatures, and hyposaline (meltwater) conditions in summer, as well as long periods of ice and snow cover in winter. From the few data available, it seems that these organisms can easily cope with these environmental extremes. The underlying physiological mechanisms that allow growth and photosynthesis to continue under widely varying abiotic parameters, along with vertical migration and heterotrophy, and biochemical features such as a pronounced fatty-acid metabolism
and silicate incorporation are discussed. Existing gaps in our knowledge of benthic diatoms in Kongsfjorden, such as the chemical ecology of biotic interactions, need to be filled. In addition, since many of the underlying molecular acclimation mechanisms are poorly understood, modern approaches based on transcriptomics,
proteomics, and/or metabolomics, in conjunction with cell biological and biochemical techniques, are urgently needed. Climate change models for the Arctic predict other multifactorial stressors, such as an increase in precipitation and permafrost thawing, with consequences for the shallow-water regions. Both precipitation and permafrost thawing are likely to increase nutrient-enriched, turbid freshwater runoff and may locally counteract the expected increase in coastal radiation availability. So far, complex interactions among factors, as well as the full genetic diversity and physiological plasticity of Arctic benthic diatoms, have only rarely been considered. The limited existing information is described and discussed in this review
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