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Contribution of black carbon and desert dust to aerosol absorption in the atmosphere of the Eastern Arabian Peninsula
Mohamed M. K. Mahfouz, Gregor Skok, Jean Sciare, Michael Pikridas, M. R. Alfarra, Shamjad Moosakutty, Bálint Alföldy, Matic Ivančič, Martin Rigler, Asta Gregorič, Rok Podlipec, Griša Močnik, 2024, izvirni znanstveni članek

Opis: Discriminating the absorption coefficients of aerosol mineral dust and black carbon (BC) in different aerosol size fractions is a challenge because of BC's large mass absorption cross-section compared to dust. Ambient aerosol wavelength dependent absorption coefficients in supermicron and submicron size fractions were determined with a high time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. At each site, measurements were taken by co-located Aethalometers, one with a virtual impactor (VI) and the other with a PM1 cyclone to respectively collect super-micron-enhanced and submicron fractions. The combined measurement of aerosol absorption and scattering coefficients enabled the particles to be classified based on their optical properties' wavelength dependence. The classification reveals the presence of BC internally/externally mixed with different aerosols. Helium ion microscopy images provided information concerning the extent of mineral dust in the submicron fraction. The determination of absorption coefficients during dust storms and non-dust periods was used to establish the absorption Ångström exponent for dust and BC. Non-parametric wind regression, potential source contribution function and back-trajectory analysis reveal major regional sources of desert dust associated with north-westerly winds and a minor local dust contribution. In contrast, major BC sources found locally were associated with south-westerly winds with a smaller contribution made by offshore emissions transported by north-easterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets separates contributions of BC and dust to the aerosol absorption coefficient.
Ključne besede: aerosol absorption, black carbon, mineral dust, desert dust, Arabian Peninsula
Objavljeno v RUNG: 29.02.2024; Ogledov: 893; Prenosov: 6
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Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes
Q. 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: 2398; Prenosov: 0
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Investigating the use of secondary organic aerosol as seed particles in simulation chamber experiments
Jaqueline F Hamilton, M Rami Alfarra, Kevin P Wyche, Martyn W Ward, Alistair C Lewis, Gordon B McFiggans, Nicholas Good, Paul S Monks, Timo Carr, Iain R. White, Ruth M Purvis, 2011, izvirni znanstveni članek

Opis: The use of β-caryophyllene secondary organic aerosol particles as seeds for smog chamber simulations has been investigated. A series of experiments were carried out in the Manchester photochemical chamber as part of the Aerosol Coupling in the Earth System (ACES) project to study the effect of seed particles on the formation of secondary organic aerosol (SOA) from limonene photo-oxidation. Rather than use a conventional seed aerosol containing ammonium sulfate or diesel particles, a method was developed to use in-situ chamber generated seed particles from β-caryophyllene photo-oxidation, which were then diluted to a desired mass loading (in this case 4-13 μg m-3). Limonene was then introduced into the chamber and oxidised, with the formation of SOA seen as a growth in the size of oxidised organic seed particles from 150 to 325 nm mean diameter. The effect of the partitioning of limonene oxidation products onto the seed aerosol was assessed using aerosol mass spectrometry during the experiment and the percentage of m/z 44, an indicator of degree of oxidation, increased from around 5 to 8 %. The hygroscopicity of the aerosol also changed, with the growth factor for 200 nm particles increasing from less than 1.05 to 1.25 at 90 % RH. The detailed chemical composition of the limonene SOA could be extracted from the complex β-caryophyllene matrix using two-dimensional gas chromatography (GC× GC) and liquid chromatography coupled to mass spectrometry. High resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS) was used to determine exact molecular formulae of the seed and the limonene modified aerosol. The average O:C ratio was seen to increase from 0.32 to 0.37 after limonene oxidation products had condensed onto the organic seed.
Ključne besede: Aerosol, Aerosol formation, Smog chamber
Objavljeno v RUNG: 18.07.2019; Ogledov: 3182; Prenosov: 0
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