Repository of University of Nova Gorica

Search the repository
A+ | A- | Help | SLO | ENG

Query: search in
search in
search in
search in
* old and bolonia study programme

Options:
  Reset


1 - 4 / 4
First pagePrevious page1Next pageLast page
1.
Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City
L. C. Marr, Katja Džepina, Jose L. Jimenez, F. Reisen, H. L. Bethel, Janet Arey, J. S. Gaffney, N. A. Marley, Luisa T. Molina, Mario J. Molina, 2006, original scientific article

Abstract: Understanding sources, concentrations, and transformations of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particle-bound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and intercomparison of the methods. The three methods are ( 1) collection and analysis of bulk samples for time-integrated gas- and particle-phase speciation by gas chromatography/ mass spectrometry; ( 2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and ( 3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations of particle-phase PAHs typically peak at similar to 110 ng m(-3) during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentrations during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions.
Found in: osebi
Keywords: aerosol mass-spectrometer, aerodynamic diameter measurements, oxygenated organic aerosols, relative rate constants
Published: 12.04.2021; Views: 497; Downloads: 0
.pdf Fulltext (1,06 MB)

2.
Secondary organic aerosol formation from anthropogenic air pollution
Rainer Volkamer, Jose L. Jimenez, F. M. San Martini, Katja Džepina, Q. Zhang, Dara Salcedo, Luisa T. Molina, D. Worsnop, 2006, original scientific article

Abstract: The atmospheric chemistry of volatile organic compounds (VOCs) in urban areas results in the formation of 'photochemical smog', including secondary organic aerosol (SOA). State-of-the-art SOA models parameterize the results of simulation chamber experiments that bracket the conditions found in the polluted urban atmosphere. Here we show that in the real urban atmosphere reactive anthropogenic VOCs (AVOCs) produce much larger amounts of SOA than these models predict, even shortly after sunrise. Contrary to current belief, a significant fraction of the excess SOA is formed from first-generation AVOC oxidation products. Global models deem AVOCs a very minor contributor to SOA compared to biogenic VOCs (BVOCs). If our results are extrapolated to other urban areas, AVOCs could be responsible for additional 3 - 25 Tg yr(-1) SOA production globally, and cause up to - 0.1 W m(-2) additional top-of-the-atmosphere radiative cooling.
Found in: osebi
Keywords: atmospheric aerosol, atmospheric chemistry, volatile organic compounds, secondary organic aerosols
Published: 12.04.2021; Views: 466; Downloads: 0
.pdf Fulltext (638,71 KB)

3.
Detection of particle-phase polycyclic aromatic hydrocarbons in Mexico City using an aerosol mass spectrometer
Katja Džepina, Janet Arey, Linsey C. Marr, D. Worsnop, Dara Salcedo, Q. Zhang, Timothy B. Onasch, Luisa T. Molina, Mario J. Molina, Jose L. Jimenez, 2007, original scientific article

Abstract: We report the quantification of ambient particle-bound polycyclic aromatic hydrocarbons (PAHs) for the first time using a real-time aerosol mass spectrometer. These measurements were carried out during the Mexico City Metropolitan Area field study (MCMA-2003) that took place from March 29 to May 4, 2003. This was the first time that two different fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. This paper focuses on the technical aspects of PAH detection in ambient air with the Aerodyne AMS equipped with a quadrupole mass analyzer (Q-AMS), on the comparison of PAHs measured by the Q-AMS to those measured with the other two techniques, and on some features of the ambient results. PAHs are very resistant to fragmentation after ionization. Based on laboratory experiments with eight PAH standards, we show that their molecular ions, which for most particulate PAHs in ambient particles are larger than 200 amu, are often the largest peak in their Q-AMS spectra. Q-AMS spectra of PAH are similar to those in the NIST database, albeit with more fragmentation. We have developed a subtraction method that allows the removal of the contribution from non-PAH organics to the ion signals of the PAHs in ambient data. We report the mass concentrations of all individual groups of PAHs with molecular weights of 202, 216, 226 + 228, 240 + 242, 250 + 252, 264 + 266, 276 + 278, 288 + 290, 300 + 302, 316 and 326 + 328, as well as their sum as the total PAH mass concentration. The time series of the Photoelectric Aerosol Sensor (PAS) and Q-AMS PAH measurements during MCMA-2003 are well correlated, with the smallest difference between measured PAH concentrations observed in the mornings when ambient aerosols loadings are dominated by fresh traffic emissions. The Q-AMS PAH measurements are also compared to those from GC–MS analysis of filter samples. Several groups of PAHs show agreement within the uncertainties, while the Q-AMS measurements are larger than the GC–MS ones for several others. In the ambient Q-AMS measurements the presence of ions tentatively attributed to cyclopenta[cd]pyrene and dicyclopentapyrenes causes signals at m/z 226 and 250, which are significantly stronger than the signals in GC–MS analysis of filter samples. This suggests that very labile, but likely toxic, PAHs were present in the MCMA atmosphere that decayed rapidly due to reaction during filter sampling, and this may explain at least some of the differences between the Q-AMS and GC–MS measurements.
Found in: osebi
Keywords: AMS, PAH, Mexico City
Published: 11.04.2021; Views: 496; Downloads: 0
.pdf Fulltext (4,12 MB)

4.
Comparative Analysis of urban atmospheric aerosol by particle-induced X-ray emission (PIXE), proton elastic scattering analysis (PESA), and aerosol mass spectrometry (AMS)
Katja Džepina, Mario J. Molina, V. Shutthanandan, Luisa T. Molina, Dara Salcedo, K.S. Johnson, A. Laskin, Jose L. Jimenez, 2008, original scientific article

Abstract: 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.
Found in: osebi
Keywords: organic aerosols, secondary organic aerosols, Mexico City, MCMA-2003 field campaign
Published: 11.04.2021; Views: 483; Downloads: 0
.pdf Fulltext (1,74 MB)

Search done in 0 sec.
Back to top