Repozitorij Univerze v Novi Gorici

Iskanje po repozitoriju
A+ | A- | Pomoč | SLO | ENG

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju

Opcije:
  Ponastavi


91 - 100 / 248
Na začetekNa prejšnjo stran6789101112131415Na naslednjo stranNa konec
91.
Atmospheric peroxyacetyl nitrate (PAN) : a global budget and source attribution
E. V. Fischer, D. J. Jacob, R. M. Yantosca, M. P. Sulprizio, D. B. Millet, Jiandong Mao, F. Paulot, H. B. Singh, A. Roiger, Katja Džepina, 2014, izvirni znanstveni članek

Opis: Peroxyacetyl nitrate (PAN) formed in the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) is the principal tropospheric reservoir for nitrogen oxide radicals (NOx = NO + NO2). PAN enables the transport and release of NOx to the remote troposphere with major implications for the global distributions of ozone and OH, the main tropospheric oxidants. Simulation of PAN is a challenge for global models because of the dependence of PAN on vertical transport as well as complex and uncertain NMVOC sources and chemistry. Here we use an improved representation of NMVOCs in a global 3-D chemical transport model (GEOS-Chem) and show that it can simulate PAN observations from aircraft campaigns worldwide. The immediate carbonyl precursors for PAN formation include acetaldehyde (44 % of the global source), methylglyoxal (30 %), acetone (7 %), and a suite of other isoprene and terpene oxidation products (19 %). A diversity of NMVOC emissions is responsible for PAN formation globally including isoprene (37 %) and alkanes (14 %). Anthropogenic sources are dominant in the extratropical Northern Hemisphere outside the growing season. Open fires appear to play little role except at high northern latitudes in spring, although results are very sensitive to plume chemistry and plume rise. Lightning NOx is the dominant contributor to the observed PAN maximum in the free troposphere over the South Atlantic.
Ključne besede: peroxyacetyl nitrate, non-methane volatile organic compounds, global 3-D chemical transport model, GEOS-chem
Objavljeno v RUNG: 11.04.2021; Ogledov: 2263; Prenosov: 0
Gradivo ima več datotek! Več...

92.
Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory : a case study with a long-range transported biomass burning plume
Katja Džepina, Claudio Mazzoleni, Paulo Fialho, Swarup China, Bo Zhang, R. Chris Owen, D. Helmig, J. Hueber, Sumit Kumar, J. A. Perlinger, 2015, izvirni znanstveni članek

Opis: Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m above mean sea level on Pico Island of the Azores archipelago in the North Atlantic. The observatory is located ∼ 3900 km east and downwind of North America, which enables studies of free tropospheric air transported over long distances. Aerosol samples collected on filters from June to October 2012 were analyzed to characterize organic carbon, elemental carbon, and inorganic ions. The average ambient concentration of aerosol was 0.9 ± 0.7 µg m−3 . On average, organic aerosol components represent the largest mass fraction of the total measured aerosol (60 ± 51 %), followed by sulfate (23 ± 28 %), nitrate (13 ± 10 %), chloride (2 ± 3 %), and elemental carbon (2 ± 2 %). Water-soluble organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25) collected consecutively during a pollution event were analyzed using ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 4000 molecular formulas were assigned to each of the mass spectra in the range of m/z 100–1000. The majority of the assigned molecular formulas had unsaturated structures with CHO and CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled air masses were very aged (average plume age > 12 days). These aged aerosol WSOM compounds had an average O /C ratio of ∼ 0.45, which is relatively low compared to O /C ratios of other aged aerosol. The increase in aerosol loading during the measurement period of 9/24 was linked to biomass burning emissions from North America by FLEXPART retroplume analysis and Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. This was confirmed with biomass burning markers detected in the WSOM and with the morphology and mixing state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions of phenolic species suggests that the aerosol collected at the Pico Mountain Observatory had undergone cloud processing before reaching the site. Finally, the air masses of 9/25 were more aged and influenced by marine emissions, as indicated by the presence of organosulfates and other species characteristic of marine aerosol. The change in the air masses for the two samples was corroborated by the changes in ethane, propane, and ozone, morphology of particles, as well as by the FLEXPART retroplume simulations. This paper presents the first detailed molecular characterization of free tropospheric aged aerosol intercepted at a lower free troposphere remote location and provides evidence of low oxygenation after long-range transport. We hypothesize this is a result of the selective removal of highly aged and polar species during long-range transport, because the aerosol underwent a combination of atmospheric processes during transport facilitating aqueous-phase removal (e.g., clouds processing) and fragmentation (e.g., photolysis) of components.
Ključne besede: organic aerosol, ultrahigh-resolution FT-ICR MS, electron microscopy, remote marine atmosphere, Pico Mountain Observatory
Objavljeno v RUNG: 11.04.2021; Ogledov: 2227; Prenosov: 0
Gradivo ima več datotek! Več...

93.
Morphology and mixing state of aged soot particles at a remote marine free troposphere site : implications for optical properties
Swarup China, Barbara Scarnato, Robert C. Owen, Bo Zhang, MarianT. Ampadu, Sumit Kumar, Katja Džepina, Michael P. Dziobak, Paulo Fialho, Judith A. Perlinger, 2015, izvirni znanstveni članek

Opis: The radiative properties of soot particles depend on their morphology and mixing state, but their evolution during transport is still elusive. Here we report observations from an electron microscopy analysis of individual particles transported in the free troposphere over long distances to the remote Pico Mountain Observatory in the Azores in the North Atlantic. Approximately 70% of the soot particles were highly compact and of those 26% were thinly coated. Discrete dipole approximation simulations indicate that this compaction results in an increase in soot single scattering albedo by a factor of <= 2.17. The top of the atmosphere direct radiative forcing is typically smaller for highly compact than mass-equivalent lacy soot. The forcing estimated using Mie theory is within 12% of the forcing estimated using the discrete dipole approximation for a high surface albedo, implying that Mie calculations may provide a reasonable approximation for compact soot above remote marine clouds.
Ključne besede: atmospheric aerosol, soot, long-range transport, free troposphere, single scattering albedo
Objavljeno v RUNG: 11.04.2021; Ogledov: 1997; Prenosov: 0
Gradivo ima več datotek! Več...

94.
Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean
Swarup China, Peter A. Alpert, Bo Zhang, Simeon K. Schum, Katja Džepina, Kendra Wright, R. Chris Owen, Paulo Fialho, Lynn R. Mazzoleni, Claudio Mazzoleni, 2017, izvirni znanstveni članek

Opis: Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.
Ključne besede: atmospheric aerosols, ice nucleating particles, long-range transport, optical microscopy, electron microscopy, Pico Mountain Observatory
Objavljeno v RUNG: 11.04.2021; Ogledov: 2234; Prenosov: 133
URL Povezava na celotno besedilo
Gradivo ima več datotek! Več...

95.
Molecular and physical characteristics of aerosol at a remote free troposphere site : implications for atmospheric aging
Simeon K. Schum, Bo Zhang, Katja Džepina, Paulo Fialho, Claudio Mazzoleni, Lynn R. Mazzoleni, 2018, izvirni znanstveni članek

Opis: Aerosol properties are transformed by atmospheric processes during long-range transport and play a key role in the Earth’s radiative balance. To understand the molecular and physical characteristics of free tropospheric aerosol, we studied samples collected at the Pico Mountain Observatory in the North Atlantic. The observatory is located in the marine free troposphere at 2225m above sea level, on Pico Island in the Azores archipelago. The site is ideal for the study of long-range-transported free tropospheric aerosol with minimal local influence. Three aerosol samples with elevated organic carbon concentrations were selected for detailed analysis. FLEXPART retroplumes indicated that two of the samples were influenced by North American wildfire emissions transported in the free troposphere and one by North American outflow mainly transported within the marine boundary layer. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry was used to determine the detailed molecular composition of the samples. Thousands of molecular formulas were assigned to each of the individual samples. On average ~60% of the molecular formulas contained only carbon, hydrogen, and oxygen atoms (CHO), ~ 30% contained nitrogen (CHNO), and ~ 10% contained sulfur (CHOS). The molecular formula compositions of the two wildfire-influenced aerosol samples transported mainly in the free troposphere had relatively low average O=C ratios (0:48 ± 0:13 and 0:45 ± 0:11) despite the 7–10 days of transport time according to FLEXPART. In contrast, the molecular composition of the North American outflow transported mainly in the boundary layer had a higher average O=C ratio (0:57 ± 0:17) with 3 days of transport time. To better understand the difference between free tropospheric transport and boundary layer transport, the meteorological conditions along the FLEXPART simulated transport pathways were extracted from the Global Forecast System analysis for the model grids. We used the extracted meteorological conditions and the observed molecular chemistry to predict the relative-humidity-dependent glass transition temperatures (Tg) of the aerosol components. Comparisons of the Tg to the ambient temperature indicated that a majority of the organic aerosol components transported in the free troposphere were more viscous and therefore less susceptible to oxidation than the organic aerosol components transported in the boundary layer. Although the number of observations is limited, the results suggest that biomass burning organic aerosol injected into the free troposphere is more persistent than organic aerosol in the boundary layer having broader implications for aerosol aging.
Ključne besede: secondary organic aerosols, brown carbon, particle dispersion model, ultrahigh-resolution FT-ICR MS, Pico Mountain Observatory
Objavljeno v RUNG: 10.04.2021; Ogledov: 2252; Prenosov: 0
Gradivo ima več datotek! Več...

96.
Analysis of PM[sub](10), Pb, Cd, and Ni atmospheric concentrations during domestic heating season in Sarajevo, Bosnia and Herzegovina, from 2010 to 2019
Jasna Huremović, Sabina Žero, Erna Bubalo, Minela Dacić, Amila Čeliković, Irma Musić, Midheta Bašić, Nudžeima Huseinbašić, Katja Džepina, Merjema Cepić, 2020, izvirni znanstveni članek

Opis: This paper examines atmospheric concentrations of particulate matter with an aerodynamic diameter smaller than 10 μm (PM10) and related particle-phase toxic heavy metals Cd, Ni, and Pb during domestic heating seasons from 2010 to 2019 in Sarajevo, Bosnia and Herzegovina. In total, 242 daily PM10 samples were collected using medium and high volume air samplers. The mean daily PM10 mass concentration for all measurements is 75.16 μg/m3 (with the range of 28.77–149.00 μg/m3). Variation of ambient PM10 was observed throughout the study in different years. Hourly values for PM10 measurements during two heating seasons are also presented. Metal concentrations in PM10 were analyzed by electrothermal atomic absorption spectrometry (ETAAS). Quantities of atmospheric mass concentrations of studied trace metals were observed in the following order: Pb > Ni > Cd. The mean concentrations of metals varied with Pb showing the highest concentration (ranging from 1.38 to 234.00 ng/m3), Ni ranging from 0.87 to 42.43 ng/m3, and Cd showing the lowest concentration ranging from 0.26 to 10.09 ng/m3. The concentration of Pb and Cd in PM10 was strongly correlated, suggesting a common source or dependence of these metals in PM10 in Sarajevo. Bioaccessibility of metals in the synthetic gastric juice was also estimated. The quantities of average bioaccessible metal fractions in PM10 samples showed the following trend: Cd > Pb > Ni. The health risk assessment shows that the population of Sarajevo is at increased lifetime risk of experiencing cancer because of exposure to these Cd concentrations in PM10. In addition, parallel PM10 sampling on two samplers showed that obtained results are highly comparable.
Ključne besede: air, PM10, heavy metals, Sarajevo
Objavljeno v RUNG: 09.04.2021; Ogledov: 2046; Prenosov: 0
Gradivo ima več datotek! Več...

97.
Carcinogenic organic content of particulate matter at urban locations with different pollution sources
Gordana Pehnec, Ivana Jakovljević, Ranka Godec, Zdravka Sever Štrukil, Sabina Žero, Jasna Huremović, Katja Džepina, 2020, izvirni znanstveni članek

Opis: Polycyclic aromatic hydrocarbons (PAHs) are compounds known for their adverse effects on human health. Many of them are proven carcinogens, especially those with 5 and 6 aromatic rings, which under normal tropospheric conditions are found in the particle-phase. Benzo(a)pyrene (BaP) is often measured as their general representative. Sarajevo, the capital of Bosnia and Herzegovina, is among the European cities with the poorest air quality. However, in Sarajevo PAHs are neither routinely measured within the air quality monitoring network nor have been a subject of extended, continuous field studies during the most polluted cold periods of the year. The capital of Croatia, Zagreb, is located approximately 300 km air distance north-west from Sarajevo. PAH mass concentrations in Zagreb have been measured continuously since 1994 within air quality monitoring networks. During winter 2017/2018, the SAFICA project (Sarajevo Canton Winter Field Campaign 2018) was carried out in order to characterize the chemical composition of organic and inorganic aerosol in the Sarajevo Canton. This paper presents the results of PAH measurements in the cities of Sarajevo and Zagreb at one urban location per city. Daily (24 h), continuous samples of PM10 (particulate matter with aerodynamic diameters ≤10 μm) were collected during heating season, from December 27, 2017 to February 27, 2018. Mass concentrations of eleven particle-phase PAHs in Sarajevo and Zagreb from filter samples collected during the same period were compared. The average BaP ambient mass concentrations in Sarajevo and Zagreb were 6.93 ng m−3 and 3.11 ng m−3, respectively. The contribution of BaP to the total PAH mass concentration was similar at both locations (11%). However, much higher contributions of particle-phase fluoranthene and pyrene were found in Sarajevo. Contributions of individual PAH, diagnostic ratios and factor analysis indicate that combustion of gasoline and diesel from vehicle traffic are a potential source of PAHs at both locations, as well as combustion of other liquid fossil fuels (petroleum and fuel oil). Wood burning was occasionally indicated as a PAH emission source in Zagreb, while in Sarajevo the contribution of PAHs from wood and coal combustion was more evident. Calculated value for total carcinogenic potency (TCP) of PAHs, which was estimated using toxic equivalence factors from the literature, in PM10 samples collected in Sarajevo was more than twice higher than in Zagreb (10.6 ng m−3 and 4.7 ng m−3, respectively). BaP had the highest contribution to the TCP at both locations (69 and 67%).
Ključne besede: carcinogenic potency, diagnostic ratio, factor analysis, PM10, polycyclic aromatic hydrocarbons
Objavljeno v RUNG: 09.04.2021; Ogledov: 2096; Prenosov: 0
Gradivo ima več datotek! Več...

98.
Nevidni, a vendar vseprisotni : nanomateriali
Katja Željan, 2021, intervju

Ključne besede: nanoznanost, nanotehnologija, nanodelci, elektronski mikroskopi
Objavljeno v RUNG: 04.03.2021; Ogledov: 2119; Prenosov: 0

99.
Primer Krajner: skoraj sto let stara zgodba o prostovoljni samoizolaciji iz časnika Jutro
Katja Mihurko Poniž, 2020, kratki znanstveni prispevek

Ključne besede: samoizolacija, Notranjska, časopis Jutro
Objavljeno v RUNG: 08.01.2021; Ogledov: 2016; Prenosov: 11
URL Povezava na celotno besedilo
Gradivo ima več datotek! Več...

100.
Iskanje izvedeno v 0.07 sek.
Na vrh