Herschel key program HERITAGE:A far-infrared source catalog for the Magellanic Clouds

Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE ) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). We conducted the study using the HERITAGE catalogs of point sources available from the Herschel Science Center from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 μm) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 μm) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 μm. There are 35,322 unique sources in the LMC and 7503 in the SMC. To be bright in the FIR, a source must be very dusty, and so the sources in the HERITAGE catalogs represent the dustiest populations of sources. The brightest HERITAGE sources are dominated by young stellar objects (YSOs), and the dimmest by background galaxies. We identify the sources most likely to be background galaxies by first considering their morphology (distant galaxies are point-like at the resolution of Herschel) and then comparing the flux distribution to that of the Herschel Astrophysical Terahertz Large Area Survey (ATLAS ) survey of galaxies. We find a total of 9745 background galaxy candidates in the LMC HERITAGE images and 5111 in the SMC images, in agreement with the number predicted by extrapolating from the ATLAS flux distribution. The majority of the Magellanic Cloud-residing sources are either very young, embedded forming stars or dusty clumps of the interstellar medium. Using the presence of 24 μm emission as a tracer of star formation, we identify 3518 YSO candidates in the LMC and 663 in the SMC. There are far fewer far-IR bright YSOs in the SMC than the LMC due to both the SMC's smaller size and its lower dust content. The YSO candidate lists may be contaminated at low flux levels by background galaxies, and so we differentiate between sources with a high ("probable") and moderate ("possible ") likelihood of being a YSO. There are 2493/425 probable YSO candidates in the LMC/SMC. Approximately 73% of the Herschel YSO candidates are newly identified in the LMC, and 35% in the SMC. We further identify a small population of dusty objects in the late stages of stellar evolution including extreme and post-asymptotic giant branch, planetary nebulae, and supernova remnants. These populations are identified by matching the HERITAGE catalogs to lists of previously identified objects in the literature. Approximately half of the LMC sources and one quarter of the SMC sources are too faint to obtain accurate ample FIR photometry and are unclassified.

Effect of Impeller Design on Homogeneity, Size and Strength of Pharmaceutical Granules produced by High Shear Wet Granulation

Small mixer impeller design is not tailored for granulation because impellers are intended for a wide range of processes. The aim of this research was to evaluate the performances of several impellers to provide guidance on the selection and design for the purposes of granulation. Lactose granules were produced using wet granulation with water as a binder. A Kenwood KM070 mixer was used as a standard apparatus and five impeller designs with different shapes and surface areas were used. The efficacy of granulate formation was measured by adding an optically sensitive tracer to determine variations in active ingredient content across random samples of granules from the same size classes. It was found that impeller design influenced the homogeneity of the granules and therefore can affect final product performance. The variation in active ingredient content across granules of differing size was also investigated. The results show that small granules were more potent than larger granules.

Char oxidation of torrefied biomass at high temperatures and high heating rates

The char oxidation of a torrefied biomass and its parent material was carried out in an isothermal plug flow reactor (IPFR), which is able to rapidly heat the biomass particles to a maximum temperature of 1400 °C at a heating rate of 104 °C/s, similar to the real conditions found in power plant furnaces. During each char oxidation test, the residues of biomass particles were collected and analyzed to determine the weight loss based on the ash tracer method. According to the experimental results, it can be concluded that chars produced from a torrefied biomass are less reactive than the ones produced, under the same conditions, from its raw material. The apparent kinetics of the torrefied biomass and its parent material are determined by minimizing the difference between the modeled and the experimental results. The predicted weight loss during char oxidation, using the determined kinetics, agrees well with experimental results

Effects of resistive magnetic field on fast electron divergence measured in experiments

Transport of fast electrons driven by an ultraintense laser through a tracer layer buried in solid targets is studied by particle-in-cell simulations. It is found that intense resistive magnetic fields, having a magnitude of several thousand Tesla, are generated at the interfaces of the materials due to the steep resistivity gradient between the target and tracer layer. Such magnetic fields can significantly inhibit the fast electron propagation. The electrons that can penetrate the first interface are mostly confined in the buried layer by the magnetic fields and cause heating of the tracer layer. The lateral extent of the heated region can be significantly larger than that of the relativistic electron beam. This finding suggests that the relativistic electron divergence inferred from Ká x-ray emission in experiments might be overestimated.

Supersolar Ni/Fe production in the Type IIP SN 2012ec

SN 2012ec is a Type IIP supernova (SN) with a progenitor detection and comprehensive photospheric phase observational coverage. Here, we present Very Large Telescope and Public ESO Spectroscopic Survey of Transient Objects observations of this SN in the nebular phase. We model the nebular [O I] lambda lambda 6300, 6364 lines and find their strength to suggest a progenitor main-sequence mass of 13-15 M-circle dot. SN2012ec is unique among hydrogen-rich SNe in showing a distinct line of stable nickel [Ni II] lambda 7378. This line is produced by Ni-58, a nuclear burning ash whose abundance is a sensitive tracer of explosive burning conditions. Using spectral synthesis modelling, we use the relative strengths of [Ni II] lambda 7378 and [Fe II] lambda 7155 (the progenitor of which is Ni-56) to derive a Ni/Fe production ratio of 0.20 +/- 0.07 (by mass), which is a factor 3.4 +/- 1.2 times the solar value. High production of stable nickel is confirmed by a strong [Ni II] 1.939 mu m line. This is the third reported case of a core-collapse SN producing a Ni/Fe ratio far above the solar value, which has implications for core-collapse explosion theory and galactic chemical evolution models.

The Evaluation and Quantitation of Dihydrogen Metabolism Using Deuterium Isotope in Rats

Purpose: Despite the significant interest in molecular hydrogen as an antioxidant in the last eight years, its quantitative metabolic parameters in vivo are still lacking, as is an appropriate method for determination of hydrogen effectivity in the mammalian organism under various conditions.

Basic Procedures: Intraperitoneally-applied deuterium gas was used as a metabolic tracer and deuterium enrichment was determined in the body water pool. Also, in vitro experiments were performed using bovine heart submitochondrial particles to evaluate superoxide formation in Complex I of the respiratory chain.

Main Findings: A significant oxidation of about 10% of the applied dose was found under physiological conditions in rats, proving its antioxidant properties. Hypoxia or endotoxin application did not exert any effect, whilst pure oxygen inhalation reduced deuterium oxidation. During in vitro experiments, a significant reduction of superoxide formation by Complex I of the respiratory chain was found under the influence of hydrogen. The possible molecular mechanisms of the beneficial effects of hydrogen are discussed, with an emphasis on the role of iron sulphur clusters in reactive oxygen species generation and on iron species-dihydrogen interaction.

Principal Conclusions: According to our findings, hydrogen may be an efficient, non-toxic, highly bioavailable and low-cost antioxidant supplement for patients with pathological conditions involving ROS-induced oxidative stress.

Mineralisation of 2,4-dichlorophenol and glucose placed into the same or different hydrological domains as a bacterial inoculant

The spatial location of microorganisms in the soil three-dimensional structure with respect to their substrates plays an important role in the persistence and turnover of natural and xenobiotic organic compounds. To study the effect of spatial location on the mineralisation of ¹⁴C-2,4-dichlorophenol (2,4-DCP, 0.15 or 0.31 μmol g^-1) and ¹⁴C-glucose (2.77 μmol g^-1), columns packed with autoclaved soil aggregates (2-5 mm) were used. Using a chloride tracer of water movement, the existence of 'immobile' water, which was by-passed by preferentially flowing 'mobile' water, was demonstrated. By manipulation of the soil moisture content, the substrates were putatively placed to these conceptual hydrological domains (immobile and mobile water). Leaching studies revealed that approximately 1.7 (glucose) and 3.4 (2.4-DCP) times the amount of substrate placed in mobile water was recovered in the first 4 fractions of leachate when compared to substrate placed in immobile water. The marked difference in the breakthrough curves was taken as evidence of successful substrate placement. The 2,4-DCP degrading bacterium, Burkholderia sp. RASCc2, was inoculated in mobile water (1.8-5.2 × 10⁷ cells g^-1 soil) and parameters (asymptote, time at maximum rate, calculated maximum rate) describing the mineralisation kinetics of 2,4-DCP and glucose previously added to immobile or mobile water domains were compared, For glucose, there was no significant effect (P > 0.1) of substrate placement on any of the mineralisation parameters. However, substrate placement had a significant effect (P < 0.05) on parameters describing 2,4-DCP mineralisation. In particular, 2,4-DCP added in mobile water was mineralised with a greater maximum rate and with a reduced time at maximum rate when compared to 2,4-DCP added to immobile water. The difference in response between the two test substrates may reflect the importance of sorption in controlling the spatial bioavailability of compounds in soil. © 2002 Elsevier Science Ltd. All rights reserved.

Balancing the (carbon) budget: Using linear inverse models to estimate carbon flows and mass-balance 13C:15N labelling experiments in low oxygen sediments.

Over 1 million km² of seafloor experience permanent low-oxygen conditions within oxygen minimum zones (OMZs). OMZs are predicted to grow as a consequence of climate change, potentially affecting oceanic biogeochemical cycles. The Arabian Sea OMZ impinges upon the western Indian continental margin at bathyal depths (150 - 1500 m) producing a strong depth dependent oxygen gradient at the sea floor. The influence of the OMZ upon the short term processing of organic matter by sediment ecosystems was investigated using in situ stable isotope pulse chase experiments. These deployed doses of ¹³C:¹⁵N labeled organic matter onto the sediment surface at four stations from across the OMZ (water depth 540 - 1100 m; [O₂] = 0.35 - 15 μM). In order to prevent experimentally anoxia, the mesocosms were not sealed. ¹³C and ¹⁵N labels were traced into sediment, bacteria, fauna and ¹³C into sediment porewater DIC and DOC. However, the DIC and DOC flux to the water column could not be measured, limiting our capacity to obtain mass-balance for C in each experimental mesocosm. Linear Inverse Modeling (LIM) provides a method to obtain a mass-balanced model of carbon flow that integrates stable-isotope tracer data with community biomass and biogeochemical flux data from a range of sources. Here we present an adaptation of the LIM methodology used to investigate how ecosystem structure influenced carbon flow across the Indian margin OMZ. We demonstrate how oxygen conditions affect food-web complexity, affecting the linkages between the bacteria, foraminifera and metazoan fauna, and their contributions to benthic respiration. The food-web models demonstrate how changes in ecosystem complexity are associated with oxygen availability across the OMZ and allow us to obtain a complete carbon budget for the stationa where stable-isotope labelling experiments were conducted.

Characterizing Aquifer Heterogeneity Using Bacterial and Bacteriophage Tracers

Gravel aquifers act as important potable water sources in central western Europe yet they are subject to numerous contamination pressures. Compositional and textural heterogeneity makes protection zone delineation around groundwater supplies in these units challenging; artificial tracer testing aids characterization. This paper reappraises previous tracer test results in light of new geological and microbiological data. Comparative passive gradient testing, using a fluorescent solute (Uranine), virus (H40/1 bacteriophage), and comparably sized bacterial tracers Escherichia coli and Pseudomonas putida, was used to investigate a calcareous gravel aquifer’s ability to remove microbiological contaminants at a test site near Munich, Germany. Test results revealed E. coli relative recoveries could exceed those of H40/1 at monitoring wells 10 m and 20 m from an injection well by almost four times; P. putida recoveries varied by a factor of up to three between wells. Application of filtration theory suggested greater attenuation of H40/1 relative to similarly charged E. coli occurred due to differences in microorganism size, while estimated collision efficiencies appeared comparable. By contrast, more positively charged P. putida experienced greater attenuation at one monitoring point, while lower attenuation rates at the second location indicated the influence of geochemical heterogeneity. Test findings proved consistent with observations from nearby fresh outcrops that suggested thin open framework gravel beds dominated mass transport in the aquifer, while discrete intervals containing stained clasts reflect localized geochemical heterogeneity. Study results highlight the utility of reconciling outcrop observations with artificial tracer test responses, using microbiological tracers with well-defined properties, to characterize aquifer heterogeneity.

Carbon and nitrogen uptake of calcareous benthic foraminifera along a depth-related oxygen gradient in the OMZ of the Arabian Sea

Foraminifera are an important faunal element of the benthos in oxygen-depleted settings such as Oxygen Minimum Zones (OMZs) where they can play a relevant role in the processing of phytodetritus. We investigated the uptake of phytodetritus (labeled with 13C and 15N) by cal-careous foraminifera in the 0-1 cm sediment horizon under different oxygen concentrations within the OMZ in the eastern Arabian Sea. The in situ tracer experiments were carried out along a depth transect on the Indian margin over a period of 4 to 10 days. The uptake of phy-todetrital carbon within 4 days by all investigated species shows that phytodetritus is a rele-vant food source for foraminifera in OMZ sediments. The decrease of total carbon uptake from 540 to 1100 m suggests a higher demand for carbon by species in the low-oxygen core region of the OMZ or less food competition with macrofauna. Especially Uvigerinids showed high uptake of phytodetrital carbon at the lowest oxygenated site. Variation in the ratio of phytodetrital carbon to nitrogen between species and sites indicates that foraminiferal carbon and nitrogen use can be decoupled and different nutritional demands are found between spe-cies. Lower ratio of phytodetrital carbon and nitrogen at 540 m could hint for greater demand or storage of food-based nitrogen, ingestion or hosting of bacteria under almost anoxic condi-tions. Shifts in the foraminiferal assemblage structure (controlled by oxygen or food availabil-ity) and in the presence of other benthic organisms account for observed changes in the pro-cessing of phytodetritus in the different OMZ habitats. Foraminifera dominate the short-term processing of phytodetritus in the OMZ core but are less important in the lower OMZ bounda-ry region of the Indian margin as biological interactions and species distribution of foraminifera change with depth and oxygen levels.

Radioimmunoassay Quantitation of Neuropeptide Y (NPY) in Human Dental Pulps

Neuropeptide Y (NPY) is a 36 amino acid peptide that is abundantly expressed in both the central and peripheral nervous systems. NPY has previously been shown to be present in human dental pulp although its exact role in pulpal health and disease remains to be fully elucidated. In addition to serving a neurotransmitter role, NPY may also have a role in modulating the pulpal response to injury and inflammation. Indeed NPY is known to be a potent vasoconstrictor in a range of tissues. Recent work by our research group has demonstrated changes in sensory neuropeptide levels measured by radioimmunoassay (RIA) in healthy and carious teeth. In addition to elevated levels of sensory neuropeptides, it is also possible that the carious process is associated with increased levels of autonomic neuropeptides such as NPY. Objectives: The aim of the present study was to undertake a comprehensive quantitative RIA analysis of NPY expression in human dental pulps from carious and non-carious teeth. Methods: A total of 22 non-carious and 46 carious teeth were included in the study. NPY was measured in all samples using RIA. Briefly, the RIA system consisted of a total volume of 400 ul, comprising 100 ul anti-NPY antibody (Peninsula Laboratories), 200 ul human NPY synthetic standard or pulp sample, and 100 ul of 125I-labelled NPY as radioactive tracer. Results: The mean concentration of NPY in non-carious teeth was found to be 4.28 ng/g (4.34 SD) compared to 9.57 ng/g (9.39 SD) in carious teeth. Using ANOVA the difference in NPY levels between the non-carious group and the carious group was found to be statistically significant (p= 0.003). Conclusion: The significant increase in the levels of NPY in carious dental pulps reported in this study provides evidence for a role for NPY in the pulpal response to caries.

Closed circuit rebreathing to achieve inert gas wash-in for multiple breath wash-out

Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2 accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be delivered and it would not alter wash-out parameters. Computer modelling was used to assess the impact of the rebreathe method on wash-in efficiency. Clinical testing of open and closed circuit wash-in–wash-out was performed in healthy controls and adult patients with cystic fibrosis (CF) using a circuit with an effective CO2 scrubber and a refined wash-in protocol. Wash-in efficiency was enhanced by rebreathing. There was no difference in mean lung clearance index between the two wash-in methods for controls (6.5 versus 6.4; p=0.2, n=12) or patients with CF (10.9 versus 10.8; p=0.2, n=19). Test time was reduced by rebreathe wash-in (156 versus 230 s for CF patients, p<0.001) and both methods were well tolerated. End wash-in CO2 was maintained below 2% in most cases. Rebreathe–wash-in is a promising development that, when correctly deployed, reduces wash-in time and facilitates portable MBW testing. For mild CF, wash-out outcomes are equivalent to an open circuit.

Numerical modelling of radionuclide migration in near-surface systems

Em todo o mundo são usados, hoje em dia, modelos numéricos hidrogeoquímicos para simular fenómenos naturais e fenómenos decorrentes de actividades antrópicas. Estes modelos ajudam-nos a compreender o ambiente envolvente, a sua variabilidade espacial e evolução temporal. No presente trabalho apresenta-se o desenvolvimento de modelos numéricos hidrogeoquímicos aplicados no contexto do repositório geológico profundo para resíduos nucleares de elevada actividade. A avaliação da performance de um repositório geológico profundo inclui o estudo da evolução geoquímica do repositório, bem como a análise dos cenários de mau funcionamento do repositório, e respectivas consequências ambientais. Se se escaparem acidentalmente radionuclídeos de um repositório, estes poderão atravessar as barreiras de engenharia e barreiras naturais que constituem o repositório, atingindo eventualmente, os ecosistemas superficiais. Neste caso, os sedimentos subsuperficiais constituem a última barreira natural antes dos ecosistemas superficiais. No presente trabalho foram desenvolvidos modelos numéricos que integram processos biogeoquímicos, geoquímicos, hidrodinâmicos e de transporte de solutos, para entender e quantificar a influência destes processos na mobilidade de radionuclídeos em sistemas subsuperficiais. Os resultados alcançados reflectem a robustez dos instrumentos numéricos utilizados para desenvolver simulações descritivas e predictivas de processos hidrogeoquímicos que influenciam a mobilidade de radionuclídeos. A simulação (descritiva) de uma experiência laboratorial revela que a actividade microbiana induz a diminuição do potencial redox da água subterrânea que, por sua vez, favorece a retenção de radionuclídeos sensíveis ao potencial redox, como o urânio. As simulações predictivas indicam que processos de co-precipitação com minerais de elementos maioritários, precipitação de fases puras, intercâmbio catiónico e adsorção à superfície de minerais favorecem a retenção de U, Cs, Sr e Ra na fase sólida de uma argila glaciar e uma moreia rica em calcite. A etiquetagem dos radionuclídeos nas simulações numéricas permitiu concluir que a diluição isotópica joga um papel importante no potencial impacte dos radionuclídeos nos sistemas subsuperficiais. A partir dos resultados das simulações numéricas é possivel calcular coeficientes de distribuição efectivos. Esta metodologia proporciona a simulação de ensaios de traçadores de longa duração que não seriam exequíveis à escala da vida humana. A partir destas simulações podem ser obtidos coeficientes de retardamento que são úteis no contexto da avaliação da performance de repositórios geológicos profundos.

Contribution of biomass combustion to air pollutant emissions

In Portugal, it was estimated that around 1.95 Mton/year of wood is used in residential wood burning for heating and cooking. Additionally, in the last decades, burnt forest area has also been increasing. These combustions result in high levels of toxic air pollutants and a large perturbation of atmospheric chemistry, interfere with climate and have adverse effects on health. Accurate quantification of the amounts of trace gases and particulate matter emitted from residential wood burning, agriculture and garden waste burning and forest fires on a regional and global basis is essential for various purposes, including: the investigation of several atmospheric processes, the reporting of greenhouse gas emissions, and quantification of the air pollution sources that affect human health at regional scales. In Southern Europe, data on detailed emission factors from biomass burning are rather inexistent. Emission inventories and source apportionment, photochemical and climate change models use default values obtained for US and Northern Europe biofuels. Thus, it is desirable to use more specific locally available data. The objective of this study is to characterise and quantify the contribution of biomass combustion sources to atmospheric trace gases and aerosol concentrations more representative of the national reality. Laboratory (residential wood combustion) and field (agriculture/garden waste burning and experimental wildland fires) sampling experiments were carried out. In the laboratory, after the selection of the most representative wood species and combustion equipment in Portugal, a sampling program to determine gaseous and particulate matter emission rates was set up, including organic and inorganic aerosol composition. In the field, the smoke plumes from agriculture/garden waste and experimental wildland fires were sampled. The results of this study show that the combustion equipment and biofuel type used have an important role in the emission levels and composition. Significant differences between the use of traditional combustion equipment versus modern equipments were also observed. These differences are due to higher combustion efficiency of modern equipment, reflecting the smallest amount of particulate matter, organic carbon and carbon monoxide released. With regard to experimental wildland fires in shrub dominated areas, it was observed that the largest organic fraction in the samples studied was mainly composed by vegetation pyrolysis products. The major organic components in the smoke samples were pyrolysates of vegetation cuticles, mainly comprising steradienes and sterol derivatives, carbohydrates from the breakdown of cellulose, aliphatic lipids from vegetation waxes and methoxyphenols from the lignin thermal degradation. Despite being a banned practice in our country, agriculture/garden waste burning is actually quite common. To assess the particulate matter composition, the smoke from three different agriculture/garden residues have been sampled into 3 different size fractions (PM2.5, PM2.5-10 and PM>10). Despite distribution patterns of organic compounds in particulate matter varied among residues, the amounts of phenolics (polyphenol and guaiacyl derivatives) and organic acids were always predominant over other organic compounds in the organosoluble fraction of smoke. Among biomarkers, levoglucosan, β-sitosterol and phytol were detected in appreciable amounts in the smoke of all agriculture/garden residues. In addition, inositol may be considered as an eventual tracer for the smoke from potato haulm burning. It was shown that the prevailing ambient conditions (such as high humidity in the atmosphere) likely contributed to atmospheric processes (e.g. coagulation and hygroscopic growth), which influenced the particle size characteristics of the smoke tracers, shifting their distribution to larger diameters. An assessment of household biomass consumption was also made through a national scale survey. The information obtained with the survey combined with the databases on emission factors from the laboratory and field tests allowed us to estimate the pollutant amounts emitted in each Portuguese district. In addition to a likely contribution to the improvement of emission inventories, emission factors obtained for tracer compounds in this study can be applied in receptor models to assess the contribution of biomass burning to the levels of atmospheric aerosols and their constituents obtained in monitoring campaigns in Mediterranean Europe.

Distribuição por tamanhos do aerosol atmosférico na Península Ibérica

Um dos principais fatores que afetam negativamente a qualidade do ambiente em muitas cidades em todo o mundo é o material particulado (PM). A sua presença na atmosfera pode ter impactos negativos na saúde humana, clima, património edificado e ecossistemas. Muitos dos estudos realizados em áreas urbanas focam apenas as frações respiráveis (PM10 e PM2,5). No entanto, os processos de formação, a identificação das fontes emissoras e os efeitos dependem muito da distribuição granulométrica das partículas. A atenção tem recaído na análise de hidrocarbonetos poliaromáticos (PAHs), devida à sua carcinogenicidade e a informação disponível sobre outros compostos é escassa. O presente estudo consistiu na obtenção do PM distribuído por diferentes frações de tamanho e na análise detalhada da sua composição química, em dois locais urbanos da Península Ibérica (Madrid e Lisboa). Dado que os veículos representam uma das principais fontes emissoras em ambientes urbanos, efetuou-se uma caracterização mais detalhada deste tipo de emissões, conduzindo uma campanha de amostragem num túnel rodoviário (Marquês de Pombal, Lisboa). As amostragens, em ambas as cidades, decorreram durante um mês, quer no verão quer no inverno, em dois locais urbanos distintos, um junto a uma via com influência de tráfego e outro numa área urbana de fundo. No túnel a amostragem foi realizada apenas durante uma semana. Em Madrid e no túnel, o PM foi recolhido utilizando um amostrador de elevado volume com impactor em cascata com quatro tamanhos: 10-2,5, 2,5-0,95, 0,95-0,49 e < 0,49 μm. Em Lisboa, foi utilizado um impactor em cascata com apenas dois tamanhos, 10- 2,5 e < 2,5 μm. As amostras foram quimicamente analisadas e determinadas as concentrações de compostos carbonados (OC, EC e carbonatos), iões inorgânicos solúveis em água (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+),metais e compostos orgânicos. Em Madrid, as concentrações médias de PM10 foram 44 e 48% maiores nas amostras recolhidas junto à estrada do que as de fundo urbano no verão e inverno, respetivamente. A fração grosseira e o PM0,5 apresentaram concentrações mais elevadas no verão do que no inverno devido às condições climatéricas pouco usuais. No verão, as amostragens decorreram num mês em que as temperaturas foram muito elevadas e em que ocorreram vários episódios de intrusão de poeira africana. Durante o período de amostragem de inverno, as temperaturas foram muito baixas e registaram-se vários dias de precipitação quer sob a forma de chuva, quer sob a forma de neve. As situações meteorológicas sinóticas mais comuns, incluindo aquelas que causam o transporte de massas de ar com poeiras Africanas, foram identificadas em ambas as estações do ano. As concentrações mássicas de PM10, EC e OC foram encontrados predominantemente na fração de tamanho ultrafino em ambos os locais de amostragem e estações do ano. Nas restantes frações não se observou nenhuma tendência sazonal. O carbono orgânico secundário (SOC) mostrou um claro padrão sazonal, com concentrações muito mais elevadas no verão do que no inverno, em ambos os lugares. A partir do balanço mássico de iões, observou-se que, no verão, a formação de compostos inorgânicos secundários (SIC) conduziu a um enriquecimento pouco comum de Ca2+ na fração submicrométrica, quer nas amostras de tráfego, quer em fundo urbano. Os alcanos, PAHs, os álcoois e os ácidos foram as classes de compostos orgânicos identificados e quantificados no material particulado. Globalmente, representaram 0,26 e 0,11 μg m−3 no verão e inverno, respetivamente, no local de tráfego e 0,28 e 0,035 μg m−3 na área urbana de fundo. Os diferentes compostos orgânicos também apresentaram padrões sazonais, sugerindo fontes de emissão (e.g. escapes dos veículos e fontes biogénicas) ou processos de formação com contribuições variáveis ao longo do ano. As concentrações de benzoapireno equivalente foram menores que 1 ng m-3 e o risco carcinogénico estimado é baixo. No verão, os maiores enriquecimentos de metais ocorreram na fração submicrométrica, e no inverno na fração grosseira. No verão, os enriquecimentos foram ≥ 80% para o Mn, Ni, Cu, Zn, Cd, Sb e Co, no inverno, estes traçadores de emissões do tráfego foram menores, exceto para o Zn. Em Lisboa, a concentração média de PM10 foi de 48 μg m-3 no verão e de 44 μg m-3 no inverno, junto à estrada. Na área de fundo urbano, registaram-se níveis comparáveis nas duas estações (27 μg m-3 e 26 μg m-3). A média do rácio PM2,5/PM10 foi de 65% no verão e 44% no inverno na área de tráfego e 62% e 59% na área urbana de fundo. Estes resultados significam que o PM2,5 é um dos principais contaminantes que afetam a qualidade do ar no centro da cidade de Lisboa. A relação OC/EC, que reflete a composição das emissões de combustão dos veículos, variou entre 0,3 e 0,4 no interior do túnel. Os rácios de OC/EC mínimos obtidos junto às vias de tráfego em Madrid e em Lisboa encontram-se entre os do túnel e os registados em atmosferas urbanas de fundo, sugerindo que os valores mínimos habitualmente obtidos para este parâmetro em ambientes urbanos abertos sobrestimam as emissões diretas de OC pelo transporte rodoviário. Espera-se que os resultados deste trabalho contribuam para suprir, pelo menos em parte, as lacunas de informação quer sobre a composição de várias granulometrias de PM, quer sobre fontes e processos de formação em atmosferas urbanas. Como a exposição a poluentes do ar ultrapassa o controle dos indivíduos e exige ação das autoridades públicas a nível nacional, regional e até mesmo internacional, é importante propor medidas mitigadoras focadas nas principais fontes de emissão identificadas.