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1.
Comparing black-carbon- and aerosol-absorption-measuring instruments : a new system using lab-generated soot coated with controlled amounts of secondary organic matter
Daniel M. Kalbermatter, Griša Močnik, Luka Drinovec, Bradley Visser, Jannis Röhrbein, Matthias Oscity, Ernest Weingartner, Antti-Pekka Hyvärinen, Konstantina Vasilatou, 2022, complete scientific database of research data

Abstract: A preprint of the publication can be found here: AMTD - Response of black carbon and aerosol absorption measuring instruments to laboratory-generated soot coated with controlled amounts of secondary organic matter (copernicus.org) (doi.org/10.5194/amt-2021-214). The files correspond to the raw data sets used for Figures 3 and 4 of the aforementioned publication. The date and start/stop time of the measurements are listed in the file "overview_measurements".
Keywords: aerosol absorption coefficient, black carbon, absorption enhancement
Published in RUNG: 19.03.2024; Views: 156; Downloads: 2
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2.
Phenomenology of organic aerosols light absorption in Europe based on in situ surface observations
Jordi Rovira, Jesús Yus-Díez, Griša Močnik, 2024, published scientific conference contribution abstract

Abstract: Both chamber and field experiments have shown that a fraction of organic aerosols (OA), called brown carbon (BrC), can efficiently absorb UV-VIS radiation with important effects on radiation balance. However, the optical properties of BrC, and its climate effects, remain poorly understood because a variety of chemical compositions are involved and their fractions vary with source and formation process. We present a phenomenology of OA light absorption in Europe using Aethalometer (AE) data. AE data were used to calculate the black carbon (BC) and BrC contribution to the total measured absorption in the UV-VIS spectral range (babs,BC(l), babsBrC(l)). Fig. 1 shows the BrC absorption at 370 nm and shows that the BrC absorption was on average higher in urban than in rural sites. Figure 1. Map of BrC absorption in rural and urban sites. At 18 out of 41 sites, simultaneous ACSM (Aerosol Chemical Speciation Monitor) data were available allowing reporting the mass absorption cross-section (MAC), the imaginary refractive index (k), the k Angström Exponent (w) of OA particles and OA sources. We compared the experimental data the with Saleh’s classification, that groups BrC in four optical classes, namely very weakly (VW-BrC), weakly (W-BrC), moderately (M-BrC) and strongly (S-BrC) absorbing BrC. Preliminary results show that both MAC and k of POA sources were higher compared to SOA sources and that BBOA (biomass burning OA) followed by CCOA (coal combustion OA) and HOA (hydrocarbon-like OA) dominated the absorption by BrC.  Data reported indicate a relationship between w and k with higher w associated to less absorbing OA particles. With this work we provide a robust experimental framework that can be used to better constrain the climate effect of OA particles represented in climate models. In our results we found that most of the measured ambient OA particles present from W to M absorption properties. Variations in OA k and w depend on the relative contribution of POA compared to SOA as also reflected by the higher k observed in winter compared to summer. Our results also demonstrate a strong variation of OA optical properties in Europe thus further confirming the complexity of OA absorption properties. This work was supported by the FOCI Project (G.A. 101056783) and ARRS P1-0385. Action Cost COLOSSAL. We thank the COLOSSAL Team for providing OA sources and AE33 data. Chen et al (2022). Env. Int. 166, 107325. Nakao et al (2013). Atm. Env. 68, 273-277. Canagaratna et al (2015). Atmos. Chem. Phys. 15, 253-272. Saleh et al (2020). Curr. Pollution Rep. 6, 90–104.
Keywords: black carbon, brown carbon, aerosol absorption coefficient
Published in RUNG: 18.03.2024; Views: 167; Downloads: 2
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3.
Aerosol light extinction coefficient closure : comparison of airborne in-situ measurements with LIDAR measurements during JATAC/CAVA-AW 2021/2022 campaigns
Marija Bervida, Jesús Yus-Díez, Luka Drinovec, Uroš Jagodič, Blaž Žibert, Matevž Lenarčič, Griša Močnik, 2024, published scientific conference contribution abstract

Abstract: The JATAC campaign in September 2021 and September 2022 on and above Cape Verde Islands resulted in a large in-situ and remote measurement dataset. Its main objective was the calibration and validation of the ESA satellite Aeolus ALADIN Lidar. The campaign also featured secondary scientific objectives related to climate change. Constraining remote sensing measurements with those provided by in-situ instrumentation is crucial for proper characterization and accurate description of the 3-D structure of the atmosphere.We present the results performed with an instrumented light aircraft (Advantic WT-10) set-up for in-situ aerosol measurements. Twenty-seven flights were conducted over the Atlantic Ocean at altitudes around and above 3000 m above sea level during intense dust transport events. Simultaneous measurements with PollyXT, and eVe ground-based lidars took place, determining the vertical profiles of aerosol optical properties, which were also used to plan the flights.The aerosol light extinction coefficient was obtained at three different wavelengths as a combination of the absorption coefficients determined using Continuous Light Absorption Photometers (CLAP) and the scattering coefficients measured with an Ecotech Aurora 4000 nephelometer, which also measured the backscatter fraction. The particle size distributions above 0.3 µm diameter were measured with two Grimm 11-D Optical Particle Size Spectrometers (OPSS). Moreover, CO2 concentration, temperature, aircraft GPS position and altitude, air and ground speed were also measured.We compare the in-situ aircraft measurements of the aerosol extinction coefficients with the AEOLUS lidar derived extinction coefficients, as well as with the ground-based eVe and PollyXT lidar extinction coefficients when measurements overlapped in space and time. The comparison was performed at the closest available wavelengths, with in-situ measurements inter/extrapolated to those of the lidar systems.In general we find an underestimation of the extinction coefficient obtained by lidars compared to the in-situ extinction coefficient. The slopes of regression lines of ground-based lidars, PollyXT and eVe, against the in-situ measurements are characterised by values ranging from 0.61 to 0.7 and R2 between 0.71 and 0.89. Comparison further suggests better agreement between Aeolus ALADIN lidar and the in-situ measurements. Relationship described by fitting the Aeolus to in-situ data is characterised by the slope value 0.76 and R2 of 0.8.The causes of better agreement of the in-situ measurements with the ALADIN lidar than with the surface based ones are being studied, with several reasons being considered: a) lower spatial and temporal resolution which homogenize the area of study in comparison with the very fine vertical variations of the aerosols, which can be detected with the surface-based measurements, impairing the comparison with highly vertically resolved ground-lidar measurements while not affecting averaged space-borne lidar; b) the effect of lower clouds/ Saharan air layers on the attenuation of the lidar signal.The presented results show the importance of the comparison of the remote with in-situ measurements for the support of the research on evolution, dynamics, and predictability of tropical weather systems and provide input into and verification of the climate models.
Keywords: LIDAR, Aeolus, ALADIN, in-situ measurements, aerosol absorption, aerosol extinction, airborne measurements
Published in RUNG: 18.03.2024; Views: 169; Downloads: 5
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4.
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, original scientific article

Abstract: 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.
Keywords: aerosol absorption, black carbon, mineral dust, desert dust, Arabian Peninsula
Published in RUNG: 29.02.2024; Views: 244; Downloads: 3
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5.
6.
Measuring the Aerosol Light Absorption Coefficient - a Not-So-Easy Task With Relevance for the Global and Regional Climate
Griša Močnik, 2022, unpublished invited conference lecture

Abstract: The photothermal interferometer measurement of aerosol absorption, using pump lasers (532, 1064 nm) and phase sensitive detection results in 4 and 6% measurement uncertainty. It is calibrated traceably to primary standards and thereby a potential reference.
Keywords: aerosol absorption, black carbon, climate change
Published in RUNG: 20.07.2022; Views: 1294; Downloads: 0
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7.
Measuring aerosol absorption directly - PTI methods to the rescue
Griša Močnik, unpublished invited conference lecture

Keywords: aerosol absorption, black carbon, climate change
Published in RUNG: 19.07.2022; Views: 1227; Downloads: 0
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8.
A dual-wavelength photothermal aerosol absorption monitor : design, calibration and performance
Luka Drinovec, Uroš Jagodič, Luka Pirker, Miha Škarabot, Mario Kurtjak, Kristijan Vidović, Luca Ferrero, Bradley Visser, Jannis Röhrbein, Ernest Weingartner, Daniel M. Kalbermatter, Konstantina Vasilatou, Griša Močnik, 2022, original scientific article

Abstract: There exists a lack of aerosol absorption measurement techniques with low uncertainties and without artefacts. We have developed the two-wavelength Photothermal Aerosol Absorption Monitor (PTAAM-2λ), which measures the aerosol absorption coefficient at 532 and 1064 nm. Here we describe its design, calibration and mode of operation and evaluate its applicability, limits and uncertainties. The 532 nm channel was calibrated with ∼ 1 µmol mol−1 NO2, whereas the 1064 nm channel was calibrated using measured size distribution spectra of nigrosin particles and a Mie calculation. Since the aerosolized nigrosin used for calibration was dry, we determined the imaginary part of the refractive index of nigrosin from the absorbance measurements on solid thin film samples. The obtained refractive index differed considerably from the one determined using aqueous nigrosin solution. PTAAM-2λ has no scattering artefact and features very low uncertainties: 4 % and 6 % for the absorption coefficient at 532 and 1064 nm, respectively, and 9 % for the absorption Ångström exponent. The artefact-free nature of the measurement method allowed us to investigate the artefacts of filter photometers. Both the Aethalometer AE33 and CLAP suffer from cross-sensitivity to scattering – this scattering artefact is most pronounced for particles smaller than 70 nm. We observed a strong dependence of the filter multiple scattering parameter on the particle size in the 100–500 nm range. The results from the winter ambient campaign in Ljubljana showed similar multiple scattering parameter values for ambient aerosols and laboratory experiments. The spectral dependence of this parameter resulted in AE33 reporting the absorption Ångström exponent for different soot samples with values biased 0.23–0.35 higher than the PTAAM-2λ measurement. Photothermal interferometry is a promising method for reference aerosol absorption measurements.
Keywords: aerosol absorption, calibration, black carbon
Published in RUNG: 28.06.2022; Views: 1133; Downloads: 25
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9.
Comparing black-carbon- and aerosol-absorption-measuring instruments – a new system using lab-generated soot coated with controlled amounts of secondary organic matter
Daniel M. Kalbermatter, Griša Močnik, Luka Drinovec, Bradley Visser, Jannis Röhrbein, Matthias Oscity, Ernest Weingartner, Antti-Pekka Hyvärinen, Konstantina Vasilatou, 2022, original scientific article

Abstract: We report on an inter-comparison of black-carbon- and aerosol-absorption-measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols was generated with elemental to total carbon (EC  TC) mass fraction ranging from about 90 % down to 10 % and single-scattering albedo (SSA at 637 nm) from almost 0 to about 0.7. A dual-spot Aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument, and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardised and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ black-carbon-measuring (BC-measuring) instruments based on realistic test aerosols.
Keywords: black carbon, aerosol absorption, secondary organic aerosol, coating
Published in RUNG: 01.02.2022; Views: 1611; Downloads: 48
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