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12.
Evaluation of recently-proposed secondary organic aerosol models for a case study in Mexico City
Katja Džepina, R. M. Volkamer, Sasha Madronich, P. Tulet, I. M. Ulbrich, Q. Zhang, C. D. Cappa, P. J. Ziemann, Jose L. Jimenez, 2009, original scientific article

Abstract: Recent field studies have found large discrepancies in the measured vs. modeled SOA mass loadings in both urban and regional polluted atmospheres. The reasons for these large differences are unclear. Here we revisit a case study of SOA formation in Mexico City described by Volkamer et al. (2006), during a photochemically active period when the impact of regional biomass burning is minor or negligible, and show that the observed increase in OA/Delta CO is consistent with results from several groups during MILAGRO 2006. Then we use the case study to evaluate three new SOA models: 1) the update of aromatic SOA yields from recent chamber experiments (Ng et al., 2007); 2) the formation of SOA from glyoxal (Volkamer et al., 2007a); and 3) the formation of SOA from primary semivolatile and intermediate volatility species (P-S/IVOC) (Robinson et al., 2007). We also evaluate the effect of reduced partitioning of SOA into POA (Song et al., 2007). Traditional SOA precursors (mainly aromatics) by themselves still fail to produce enough SOA to match the observations by a factor of similar to similar to 7. The new low-NOx aromatic pathways with very high SOA yields make a very small contribution in this high-NOx urban environment as the RO2 center dot+NO reaction dominates the fate of the RO2 center dot radicals. Glyoxal contributes several mu g m(-3) to SOA formation, with similar timing as the measurements. P-S/IVOC are estimated from equilibrium with emitted POA, and introduce a large amount of gas-phase oxidizable carbon that was not in models before. With the formulation in Robinson et al. (2007) these species have a high SOA yield, and this mechanism can close the gap in SOA mass between measurements and models in our case study. However the volatility of SOA produced in the model is too high and the O/C ratio is somewhat lower than observations. Glyoxal SOA helps to bring the O/C ratio of predicted and observed SOA into better agreement. The sensitivities of the model to some key uncertain parameters are evaluated.
Found in: ključnih besedah
Summary of found: ...SOA formation, with similar timing as the measurements. P-S/IVOC are estimated from equilibrium with emitted...
Keywords: polycyclic aromatic-hydrocarbons, positive matrix factorization, mass-spectrometry, volatility measurements
Published: 11.04.2021; Views: 405; Downloads: 0
.pdf Fulltext (1,18 MB)

13.
Evolution of organic aerosols in the atmosphere
J. H. Kroll, P. F. DeCarlo, J. David Allan, H. Coe, Katja Džepina, Jose L. Jimenez, M. R. Canagaratna, N. M. Donahue, A. S. H. Prevot, Q. Zhang, 2009, original scientific article

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state....
Keywords: secondary organic aerosol, source apportionment, aerodyne aerosol mass spectrometer, global field measurements, laboratory experiments
Published: 11.04.2021; Views: 345; Downloads: 0
.pdf Fulltext (721,30 KB)

14.
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: ključnih besedah
Summary of found: ...used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH...
Keywords: aerosol mass-spectrometer, aerodynamic diameter measurements, oxygenated organic aerosols, relative rate constants
Published: 12.04.2021; Views: 410; Downloads: 0
.pdf Fulltext (1,06 MB)

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