Publications by authors named "David Brus"

12 Publications

  • Page 1 of 1

Concentrations and Adsorption Isotherms for Amphiphilic Surfactants in PM Aerosols from Different Regions of Europe.

Environ Sci Technol 2019 Nov 10;53(21):12379-12388. Epub 2019 Oct 10.

Division for Marine and Environmental Research , Ruđer Bošković Institute , Zagreb 10000 , Croatia.

Predicting the activation of submicrometer particles into cloud droplets in the atmosphere remains a challenge. The importance of surface tension, σ (mN m), in these processes has been evidenced by several works, but information on the "surfactants" lowering σ in actual atmospheric particles remains scarce. In this work, PM aerosols from urban, coastal, and remote regions of Europe (Lyon, France, Rogoznica, Croatia, and Pallas, Finland, respectively) were investigated and found to contain amphiphilic surfactants in concentrations up to 2.8 μg m in the air and 1.3 M in the particle dry volume. In Pallas, correlations with the PM chemical composition showed that amphiphilic surfactants were present in the entire range of particle sizes, supporting recent works. This implied that they were present in hundreds to thousands of particles cm and not only in a few large particles, as it has been hypothesized. Their adsorption isotherms and critical micelle concentration (CMC) were also determined. The low CMC obtained (3 × 10-9 × 10 M) implies that surface tension depression should be significant for all the particles containing these compounds, even at activation (growth factor ∼ 10). Amphiphilic surfactants are thus likely to enhance the CCN ability of submicrometer atmospheric particles.
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http://dx.doi.org/10.1021/acs.est.9b03386DOI Listing
November 2019

Intercomparison of Small Unmanned Aircraft System (sUAS) Measurements for Atmospheric Science during the LAPSE-RATE Campaign.

Sensors (Basel) 2019 05 10;19(9). Epub 2019 May 10.

Cooperative Institute for Research in Environmental Sciences, University of Colorado,Boulder, CO 80309, USA.

Small unmanned aircraft systems (sUAS) are rapidly transforming atmospheric research. With the advancement of the development and application of these systems, improving knowledge of best practices for accurate measurement is critical for achieving scientific goals. We present results from an intercomparison of atmospheric measurement data from the Lower Atmospheric Process Studies at Elevation-a Remotely piloted Aircraft Team Experiment (LAPSE-RATE) field campaign. We evaluate a total of 38 individual sUAS with 23 unique sensor and platform configurations using a meteorological tower for reference measurements. We assess precision, bias, and time response of sUAS measurements of temperature, humidity, pressure, wind speed, and wind direction. Most sUAS measurements show broad agreement with the reference, particularly temperature and wind speed, with mean value differences of 1.6 ± 2 . 6 ∘ C and 0.22 ± 0 . 59 m/s for all sUAS, respectively. sUAS platform and sensor configurations were found to contribute significantly to measurement accuracy. Sensor configurations, which included proper aspiration and radiation shielding of sensors, were found to provide the most accurate thermodynamic measurements (temperature and relative humidity), whereas sonic anemometers on multirotor platforms provided the most accurate wind measurements (horizontal speed and direction). We contribute both a characterization and assessment of sUAS for measuring atmospheric parameters, and identify important challenges and opportunities for improving scientific measurements with sUAS.
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http://dx.doi.org/10.3390/s19092179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6540006PMC
May 2019

A Finnish Meteorological Institute-Aerosol Cloud Interaction Tube (FMI-ACIT): Experimental setup and tests of proper operation.

J Chem Phys 2018 Sep;149(12):124201

Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland.

The Finnish Meteorological Institute-Aerosol Cloud Interaction Tube (FMI-ACIT) is a multi-purpose instrument for investigating atmospherically relevant interactions between aerosol particles and water vapor under defined laboratory conditions. This work introduces an experimental setup of FMI-ACIT for investigation of the aerosol activation and the droplet growth under supersaturated conditions. Several simulations and experimental tests were conducted to find out what the proper operational parameters are. To verify the ability of FMI-ACIT to perform as a cloud condensation nuclei (CCN) counter, activation experiments were executed using size selected ammonium sulfate [(NH)SO] particles in the size range of 10-300 nm. Supersaturations from 0.18% to 1.25% were tested by experiments with different temperature gradients. Those showed that FMI-ACIT can effectively measure CCN in this range. Measured droplet size distributions at supersaturations 0.18% and 1.25% are in good agreement with those determined by a droplet growth model.
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http://dx.doi.org/10.1063/1.5037298DOI Listing
September 2018

Homogenous nucleation rates of n-propanol measured in the Laminar Flow Diffusion Chamber at different total pressures.

J Chem Phys 2014 May;140(17):174301

Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, FI-00101 Helsinki, Finland.

Nucleation rates of n-propanol were investigated in the Laminar Flow Diffusion Chamber. Nucleation temperatures between 270 and 300 K and rates between 10(0) and 10(6) cm(-3) s(-1) were achieved. Since earlier measurements of n-butanol and n‑pentanol suggest a dependence of nucleation rates on carrier gas pressure, similar conditions were adjusted for these measurements. The obtained data fit well to results available from literature. A small positive pressure effect was found which strengthen the assumption that this effect is attributed to the carbon chain length of the n-alcohol [D. Brus, A. P. Hyvärinen, J. Wedekind, Y. Viisanen, M. Kulmala, V. Ždímal, J. Smolík, and H. Lihavainen, J. Chem. Phys. 128, 134312 (2008)] and might be less intensive for substances in the homologous series with higher equilibrium vapor pressure. A comparison with the theoretical approach by Wedekind et al. [Phys. Rev. Lett. 101, 12 (2008)] shows that the effect goes in the same direction but that the intensity is much stronger in experiments than in theory.
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http://dx.doi.org/10.1063/1.4872364DOI Listing
May 2014

Homogeneous water nucleation in a laminar flow diffusion chamber.

J Chem Phys 2010 Jun;132(24):244505

Institut für Physikalische Chemie, Universität zu Köln, Germany.

Homogeneous nucleation rates of water at temperatures between 240 and 270 K were measured in a laminar flow diffusion chamber at ambient pressure and helium as carrier gas. Being in the range of 10(2)-10(6) cm(-3) s(-1), the experimental results extend the nucleation rate data from literature consistently and fill a pre-existing gap. Using the macroscopic vapor pressure, density, and surface tension for water we calculate the nucleation rates predicted by classic nucleation theory (CNT) and by the empirical correction function of CNT by Wolk and Strey [J. Phys. Chem. B 105, 11683 (2001)]. As in the case of other systems (e.g., alcohols), CNT predicts a stronger temperature dependence than experimentally observed, whereas the agreement with the empirical correction function is good for all data sets. Furthermore, the isothermal nucleation rate curves allow us to determine the experimental critical cluster sizes by use of the nucleation theorem. A comparison with the critical cluster sizes calculated by use of the Gibbs-Thomson equation is remarkably good for small cluster sizes, for bigger ones the Gibbs-Thomson equation overestimates the cluster sizes.
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http://dx.doi.org/10.1063/1.3427537DOI Listing
June 2010

The role of sulfuric acid in atmospheric nucleation.

Science 2010 Mar;327(5970):1243-6

Leibniz-Institut für Troposphärenforschung e.V., Leipzig 04318, Germany.

Nucleation is a fundamental step in atmospheric new-particle formation. However, laboratory experiments on nucleation have systematically failed to demonstrate sulfuric acid particle formation rates as high as those necessary to account for ambient atmospheric concentrations, and the role of sulfuric acid in atmospheric nucleation has remained a mystery. Here, we report measurements of new particles (with diameters of approximately 1.5 nanometers) observed immediately after their formation at atmospherically relevant sulfuric acid concentrations. Furthermore, we show that correlations between measured nucleation rates and sulfuric acid concentrations suggest that freshly formed particles contain one to two sulfuric acid molecules, a number consistent with assumptions that are based on atmospheric observations. Incorporation of these findings into global models should improve the understanding of the impact of secondary particle formation on climate.
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http://dx.doi.org/10.1126/science.1180315DOI Listing
March 2010

Homogeneous nucleation rate measurements in supersaturated water vapor II.

J Chem Phys 2009 Aug;131(7):074507

Laboratory of Aerosol Chemistry and Physics, Institute of Chemical Process Fundamentals AS CR, v.v.i., CZ-16502 Prague, Czech Republic.

The homogeneous nucleation of water was studied experimentally in this work using a thermal diffusion cloud chamber; droplets were counted by the photomultiplier method and helium was used as a carrier gas. The nucleation rates range from 3x10(-2) to 3x10(1) cm(-3) s(-1) and six isotherms from 295 to 320 K with step of 5 K are measured. The experimental setup and obtained data are mutually compared to our previous publication [Brus et al., J. Chem. Phys. 129, 174501 (2008)], where the droplets were counted using digital photography and image processing. The molecular content of the critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of the nucleation rate of water on the saturation ratio were compared with previously published data of others, several theoretical predictions, and the former nucleation onset data. The aim of the present investigation was to show for the first time that nucleation results can be quantitatively reproduced with two different experimental setups operated in different ways.
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http://dx.doi.org/10.1063/1.3211105DOI Listing
August 2009

Homogeneous nucleation rate measurements in supersaturated water vapor.

J Chem Phys 2008 Nov;129(17):174501

Laboratory of Aerosol Chemistry and Physics, Institute of Chemical Process Fundamentals AS CR, v.v.i., Rozvojova 135, CZ-16502 Prague, Czech Republic.

The rate of homogeneous nucleation in supersaturated vapors of water was studied experimentally using a thermal diffusion cloud chamber. Helium was used as a carrier gas. Our study covers a range of nucleation rates from 3x10(-1) to 3x10(2) cm(-3) s(-1) at four isotherms: 290, 300, 310, and 320 K. The molecular content of critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of nucleation rate of water on saturation ratio were compared with the prediction of the classical theory of homogeneous nucleation, the empirical prediction of Wolk et al. [J. Chem. Phys. 117, 10 (2002)], the scaled model of Hale [Phys. Rev. A 33, 4156 (1986)], and the former nucleation onset data.
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http://dx.doi.org/10.1063/1.3000629DOI Listing
November 2008

Unraveling the "pressure effect" in nucleation.

Phys Rev Lett 2008 Sep 18;101(12):125703. Epub 2008 Sep 18.

Departament de Física Fonamental, Universitat de Barcelona, Martí i Franquès 1, Barcelona, Spain.

The influence of the pressure of a chemically inert carrier gas on the nucleation rate is one of the biggest puzzles in the research of gas-liquid nucleation. Experiments can show a positive effect, a negative effect, or no effect at all. The same experiment may show both trends for the same substance depending on temperature, or for different substances at the same temperature. We show how this ambiguous effect naturally arises from the competition of two contributions: nonisothermal effects and pressure-volume work. Our model clarifies seemingly contradictory experimental results and quantifies the variation of the nucleation ability of a substance in the presence of an ambient gas. Our findings are corroborated by molecular dynamics simulations and might have important implications since nucleation in experiments, technical applications, and nature practically always occurs in the presence of an ambient gas.
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http://dx.doi.org/10.1103/PhysRevLett.101.125703DOI Listing
September 2008

The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

J Chem Phys 2006 Jun;124(22):224304

Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, F1-00101 Helsinki, Finland.

Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.
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http://dx.doi.org/10.1063/1.2200341DOI Listing
June 2006

Homogeneous nucleation rate measurements of 1-propanol in helium: the effect of carrier gas pressure.

J Chem Phys 2006 Apr;124(16):164306

Laboratory of Aerosol Chemistry and Physics, Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Prague 6, Czech Republic.

Kinetics of homogeneous nucleation in supersaturated vapor of 1-propanol was studied using an upward thermal diffusion cloud chamber. Helium was used as a noncondensable carrier gas and the influence of its pressure on observed nucleation rates was investigated. The isothermal nucleation rates were determined by a photographic method that is independent on any nucleation theory. In this method, the trajectories of growing droplets are recorded using a charge coupled device camera and the distribution of local nucleation rates is determined by image analysis. The nucleation rate measurements of 1-propanol were carried out at four isotherms 260, 270, 280, and 290 K. In addition, the pressure dependence was investigated on the isotherms 290 K (50, 120, and 180 kPa) and 280 K (50 and 120 kPa). The isotherm 270 K was measured at 25 kPa and the isotherm 260 K at 20 kPa. The experiments confirm the earlier observations from several thermal diffusion chamber investigations that the homogeneous nucleation rate of 1-propanol tends to increase with decreasing total pressure in the chamber. In order to reduce the possibility that the observed phenomenon is an experimental artifact, connected with the generally used one-dimensional description of transfer processes in the chamber, a recently developed two-dimensional model of coupled heat, mass, and momentum transfer inside the chamber was used and results of both models were compared. It can be concluded that the implementation of the two-dimensional model does not explain the observed effect. Furthermore the obtained results were compared both to the predictions of the classical theory and to the results of other investigators using different experimental devices. Plotting the experimental data on the so-called Hale plot shows that our data seem to be consistent both internally and also with the data of others. Using the nucleation theorem the critical cluster sizes were obtained from the slopes of the individual isotherms and compared with the Kelvin prediction. The influence of total pressure on the observed isothermal nucleation rate was studied in another experiment, where not only temperature but also supersaturation was kept constant as the total pressure was changed. It was shown that the dependence of the nucleation rate on pressure gets stronger as pressure decreases.
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http://dx.doi.org/10.1063/1.2185634DOI Listing
April 2006

Homogeneous nucleation rate measurements of 1-butanol in helium: a comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamber.

J Chem Phys 2005 Jun;122(21):214506

Aerosol Laboratory, Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Prague 6, Czech Republic.

Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results.
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http://dx.doi.org/10.1063/1.1917746DOI Listing
June 2005