41. Implementation of a Markov Chain Monte Carlo method to inorganic aerosol modeling of observations from the MCMA-2003 campaign : part IIF. M. San Martini, E. J. Dunlea, R. M. Volkamer, T. B. Onasch, J. Jayne, M. R. Canagaratna, D. Worsnop, C. E. Kolb, J. H. Shorter, Katja Džepina, 2006, izvirni znanstveni članek Opis: A Markov Chain Monte Carlo model for integrating the observations of inorganic species with a thermodynamic equilibrium model was presented in Part I of this series. Using observations taken at three ground sites, i. e. a residential, industrial and rural site, during the MCMA-2003 campaign in Mexico City, the model is used to analyze the inorganic particle and ammonia data and to predict gas phase concentrations of nitric and hydrochloric acid. In general, the model is able to accurately predict the observed inorganic particle concentrations at all three sites. The agreement between the predicted and observed gas phase ammonia concentration is excellent. The NOz concentration calculated from the NOy, NO and NO2 observations is of limited use in constraining the gas phase nitric acid concentration given the large uncertainties in this measure of nitric acid and additional reactive nitrogen species. Focusing on the acidic period of 9-11 April identified by Salcedo et al. ( 2006), the model accurately predicts the particle phase observations during this period with the exception of the nitrate predictions after 10: 00 a. m. ( Central Daylight Time, CDT) on 9 April, where the model underpredicts the observations by, on average, 20%. This period had a low planetary boundary layer, very high particle concentrations, and higher than expected nitrogen dioxide concentrations. For periods when the particle chloride observations are consistently above the detection limit, the model is able to both accurately predict the particle chloride mass concentrations and provide well-constrained HCl ( g) concentrations. The availability of gas-phase ammonia observations helps constrain the predicted HCl ( g) concentrations. When the particles are aqueous, the most likely concentrations of HCl ( g) are in the sub-ppbv range. The most likely predicted concentration of HCl ( g) was found to reach concentrations of order 10 ppbv if the particles are dry. Finally, the atmospheric relevance of HCl ( g) is discussed in terms of its indicator properties for the possible influence of chlorine-mediated photochemistry in Mexico City.
Ključne besede: secondary organic aerosols, Mexico City, MCMA-2003 field campaign, thermodynamic equilibrium
Objavljeno v RUNG: 11.04.2021; Ogledov: 2143; Prenosov: 0
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42. Technical note : use of a beam width probe in an aerosol mass spectrometer to monitor particle collection efficiency in the fieldDara Salcedo, T. B. Onasch, M. R. Canagaratna, Katja Džepina, J. A. Huffman, J. Jayne, D. Worsnop, C. E. Kolb, S. Weimer, F. Drewnick, 2007, izvirni znanstveni članek Opis: Two Aerodyne Aerosol Mass Spectrometers (Q-AMS) were deployed in Mexico City, during the Mexico City Metropolitan Area field study (MCMA-2003) from 29 March - 4 May 2003 to investigate particle concentrations, sources, and processes. We report the use of a particle beam width probe (BWP) in the field to quantify potential losses of particles due to beam broadening inside the AMS caused by particle shape (nonsphericity) and particle size. Data from this probe show that no significant mass of particles was lost due to excessive beam broadening; i.e. the shape- and size-related collection efficiency (E-s) of the AMS during this campaign was approximately one. Comparison of the BWP data from MCMA-2003 with other campaigns shows that the same conclusion holds for several other urban, rural and remotes sites. This means that the aerodynamic lens in the AMS is capable of efficiently focusing ambient particles into a well defined beam and onto the AMS vaporizer for particles sampled in a wide variety of environments. All the species measured by the AMS during MCMA-2003 have similar attenuation profiles which suggests that the particles that dominate the mass concentration were internally mixed most of the time. Only for the smaller particles ( especially below 300 nm), organic and inorganic species show different attenuation versus particle size which is likely due to partial external mixing of these components. Changes observed in the focusing of the particle beam in time can be attributed, in part, to changes in particle shape (i.e. due to relative humidity) and size of the particles sampled. However, the relationships between composition, atmospheric conditions, and particle shape and size appear to be very complex and are not yet completely understood.
Ključne besede: atmospheric aerosol, organic aerosols, aerodynamic lenses, Mexico City
Objavljeno v RUNG: 11.04.2021; Ogledov: 2595; Prenosov: 0
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43. Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudesQ. Zhang, Jose L. Jimenez, M. R. Canagaratna, J. David Allan, H. Coe, I. M. Ulbrich, M. R. Alfarra, A. Takami, A. M. Middlebrook, Katja Džepina, 2007, izvirni znanstveni članek Opis: Organic aerosol (OA) data acquired by the Aerosol Mass Spectrometer (AMS) in 37 field campaigns were deconvolved into hydrocarbon-like OA (HOA) and several types of oxygenated OA (OOA) components. HOA has been linked to primary combustion emissions (mainly from fossil fuel) and other primary sources such as meat cooking. OOA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total OA in urban, urban downwind, and rural/remote sites, respectively. A case study analysis of a rural site shows that the OOA concentration is much greater than the advected HOA, indicating that HOA oxidation is not an important source of OOA, and that OOA increases are mainly due to SOA. Most global models lack an explicit representation of SOA which may lead to significant biases in the magnitude, spatial and temporal distributions of OA, and in aerosol hygroscopic properties.
Ključne besede: atmospheric aerosol, secondary organic aerosols, primary organic aerosols, aerodyne aerosol mass spectrometer
Objavljeno v RUNG: 11.04.2021; Ogledov: 2046; Prenosov: 0
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44. Comparative Analysis of urban atmospheric aerosol by particle-induced X-ray emission (PIXE), proton elastic scattering analysis (PESA), and aerosol mass spectrometry (AMS)K.S. Johnson, A. Laskin, Jose L. Jimenez, V. Shutthanandan, Luisa T. Molina, Dara Salcedo, Katja Džepina, Mario J. Molina, 2008, izvirni znanstveni članek Opis: A multifaceted approach to atmospheric aerosol analysis is often desirable infield studies where an understanding of technical comparability among different measurement techniques is essential. Herein, we report quantitative intercomparisons of particle-induced X-ray emission (PIXE) and proton elastic scattering analysis (PESA), performed offline under a vacuum, with analysis by aerosol mass spectrometry (AMS) carried out in real-time during the MCMA-2003 Field Campaign in the Mexico City Metropolitan Area. Good agreement was observed for mass concentrations of PIXE-measured sulfur (assuming it was dominated by SO42-) and AMS-measured sulfate during most of the campaign. PESA-measured hydrogen mass was separated into sulfate H and organic H mass fractions, assuming the only major contributions were (NH4)(2)SO4 and organic compounds. Comparison of the organic H mass with AMS organic aerosol measurements indicates that about 75% of the mass of these species evaporated under a vacuum. However similar to 25% of the organics does remain under a vacuum, which is only possible with low-vapor-pressure compounds, and which supports the presence of high-molecular-weight or highly oxidized organics consistent with atmospheric aging. Approximately 10% of the chloride detected by AMS was measured by PIXE, possibly in the form of metal-chloride complexes, while the majority of Cl was likely present as more volatile species including NH4Cl. This is the first comparison of PIXE/PESA and AMS and, to our knowledge, also the first report of PESA hydrogen measurements for urban organic aerosols.
Ključne besede: organic aerosols, secondary organic aerosols, Mexico City, MCMA-2003 field campaign
Objavljeno v RUNG: 11.04.2021; Ogledov: 2196; Prenosov: 0
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45. Evolution of organic aerosols in the atmosphereJose L. Jimenez, M. R. Canagaratna, N. M. Donahue, A. S. H. Prevot, Q. Zhang, J. H. Kroll, P. F. DeCarlo, J. David Allan, H. Coe, Katja Džepina, 2009, izvirni znanstveni članek Opis: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
Ključne besede: secondary organic aerosol, source apportionment, aerodyne aerosol mass spectrometer, global field measurements, laboratory experiments
Objavljeno v RUNG: 11.04.2021; Ogledov: 2186; Prenosov: 0
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46. Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal : relevance of O/C as a tracer for aqueous multiphase chemistryEleanor M. Waxman, Katja Džepina, Barbara Ervens, Julia Lee-Taylor, Bernard Aumont, Jose L. Jimenez, Sasha Madronich, Rainer Volkamer, 2013, izvirni znanstveni članek Opis: The role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry.
Ključne besede: secondary organic aerosol, glyoxal, aqueous multiphase chemistry, oxygen-to-carbon ratio, single scattering albedo
Objavljeno v RUNG: 11.04.2021; Ogledov: 2062; Prenosov: 0
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47. Atmospheric peroxyacetyl nitrate (PAN) : a global budget and source attributionE. 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: 2324; Prenosov: 0
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48. Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory : a case study with a long-range transported biomass burning plumeKatja 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: 2280; Prenosov: 0
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49. Molecular and physical characteristics of aerosol at a remote free troposphere site : implications for atmospheric agingSimeon 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: 2315; Prenosov: 0
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50. Pollutant removal with organic macrocycle-based covalent organic polymers and frameworksTina Škorjanc, Dinesh Shetty, Ali Trabolsi, 2021, pregledni znanstveni članek Opis: Air, water, and soil pollution devastate countless ecosystems and deteriorate human health. Adsorption has commonly been used as a pollutant removal technique, but ongoing materials science research is still searching for more efficient, cheaper, and scalable sorbent materials. Herein, we discuss the synthesis and pollutant-capturing abilities of covalent polymeric structures, including covalent organic polymers and covalent organic frameworks that contain organic macrocycles in the backbone of their structures. These organic macrocycles (cyclodextrin, calixarene, cucurbituril, pillararene, and porphyrin) possess cavities and functional groups that can sequester pollutants by forming supramolecular interactions. The insolubility of these materials prominently aids in their regeneration and recyclability potentials. Following a discussion on the synthetic strategies used in the polymerization of each type of macrocycle, environmental applications of these materials are presented. Here, we focus on the removal of micropollutants, charged species, metal ions, oils and organic solvents, perfluorinated substances, iodine, and volatile organic compounds.
Ključne besede: supramolecular interactions, host-guest chemistry, organic macrocycles, covalent polymers, covalent organic frameworks, environmental remediation, adsorption
Objavljeno v RUNG: 09.04.2021; Ogledov: 2148; Prenosov: 65
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