Jiří Smolík

Chemical composition of size-resolved atmospheric aerosols in the eastern Mediterranean during summer and winter

Abstract The chemical composition of aerosols has been determined in 30 size-resolved samples collected using a Berner low-pressure impactor during two campaigns conducted at a coastal site in the Eastern Mediterranean in July 2000 and in January 2001. Sulfate (SO42−) and ammonium (NH4+) have been identified as the main ionic components of the sub-micronic aerosol fraction, with SO42− accounting for up to 38% of the total fine mass and up to 65% of the total ionic mass during both seasons. On the other hand, nitrate (NO3−), chloride (Cl−), sodium (Na+) and calcium (Ca2+) were identified as the main components of the super-micron mode. The ionic organic compounds (including carboxylic, dicarboxylic and ketoacids) were distributed both between sub-micron and super-micron mode, indicating origin from both gas-to-particle conversion and heterogeneous reactions on pre-existing particles. The total water-soluble ionic organic fraction although accounting for only up to 1–2% of both coarse (>1 μm ) and fine ( μm ) mass fractions, accounts for up to 15% of the organic carbon (OC) mass. NH4+ was found to be significantly correlated to non-sea-salt sulfate (nss-SO42−), with NH4+/nss-SO42− molar ratio ranging from 1.3 to 2, the lower ratio associated with transport from the W sector. Chloride depletion was observed mainly during summer and was significantly correlated with NO3− concentrations, with a molar ratio of 0.80, indicating the reaction of nitric acid with NaCl as the main source of NO3− in the area. Total ionic mass both in the fine and coarse fraction accounted for up to 58% of the total aerosol mass during both seasons. An attempt to perform a mass closure analysis indicates that nss-SO42− and organic carbon are the main components of the fine fraction with relative contributions of 38% and 16%, respectively. In the coarse fraction, the ionic part accounts for 58%, mineral dust for 32% and the remaining non-identified part of 12–30% could be partly attributed to water.

Modeling Dry Deposition of Aerosol Particles onto Rough Surfaces

Dry deposition is a primary mechanism by which suspended particles are transported from gas onto surfaces. Prediction of this transport rate is needed in a vast range of applications, including environmental, industrial, and engineering, and in studying the impacts of aerosols. Besides air flow characteristics and properties of aerosol particles, the dry deposition velocity depends greatly on surface properties. However, existing models describe rough surfaces with only one parameter, the surface roughness height, and are therefore of limited accuracy. Here, we introduce a new, and yet simple, physical approach to account for the influence of surface roughness on the dry deposition velocity. The approach relies on a hybrid parameter that combines the surface roughness height and the peak-to-peak distance between roughness elements. Our new approach is able to predict the deposition velocity accurately, being superior to many of the earlier models, which overpredict deposition velocities by a factor as high as 25. In addition, our approach is more general and covers a wide size range of aerosol particle diameter (0.001–100 μm). Copyright 2012 American Association for Aerosol Research

Evaporation of ventilated water droplet: connection between heat and mass transfer

Heat and mass transfer from evaporating water droplets has been investigated using a wind tunnel technique. The results were compared with results of other authors and correlated by an empirical fit proposed by Clift, Grace, and Weber (Bubbles, Drops, and Particles, Academic Press, New York, 1978 [Chapters 3 and 5]). It was found that the fit gave reasonably accurate predictions for Reynolds numbers Re ranging from 0 to 400. The accuracy of the obtained expression was tested comparing measured and calculated droplet temperatures. The results agree always within 5% and usually even within 1%. This represents an experimental validation for mass and heat flux expressions commonly used in condensation and evaporation studies.

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

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.

Condensation of Supersaturated Vapors of Dioctylphthalate: Homogeneous Nucleation Rate Measurements

Homogeneous nucleation rates of dioctylphthalate (DOP) [1,2-benzenedicarboxylic acid (bis-2-ethyl hexyl ester)] ranging from 0.032 to 16.3 drops cm−3 s−1 were measured as a function of supersaturation and temperature by using an upward thermal diffusion cloud chamber. The influence of thermodiffusiophoresis was included in raw data analysis. An empirical formula was used to fit measured nucleation rates over a supersaturation range from 33 to 68 and temperatures ranging from 364 to 396 K. A comparison with earlier published data on critical supersaturations of DOP showed consistency of both measurements.

Homogeneous nucleation rate measurements in 1-pentanol vapor with helium as a buffer gas

Abstract The rate of homogeneous nucleation in supersaturated vapors of n-pentanol was studied experimentally using an upward static diffusion chamber. Helium was used as a buffer gas, holding the total pressure in the chamber at Pt=25 kPa. A recently improved photographic technique was used to determine the nucleation rate as a function of supersaturation at temperature T=260 K. This dependence was compared with predictions made by the classical theory of homogeneous nucleation. Furthermore, the influence of gaseous ions on nucleation rate was studied, and a minimum voltage across the chamber, necessary to avoid nucleation on ions, was determined. The effect of the wall heating power on nucleation was found to be negligible in the range studied.

Deposition of suspended fine particulate matter in a library

To analyse deposition of fine particulate matter (PM) on book surfaces we put twelve bunches of cellulose filters on a free shelf of the National Library in Prague, exposed them for three, six, nine, and twelve months to indoor air and analysed them after each period by Scanning Electron Microscopy (SEM) and Ion Chromatography (IC). Results showed that fine particles were deposited predominantly on the surface of the top filter but partly also on the surfaces of inner filters. It indicates fine particles penetrated between filters. The penetration and deposition of particles was also modelled as Brownian diffusion between two parallel filters. The model prediction demonstrated that fine particles penetrate between filters, with the depth of penetration limited by parallel diffusional deposition on filter surfaces. This is in qualitative agreement with SEM and IC investigations. The results show that beside the top part fine PM can deposit onto all available surfaces of books.

Comprehensive Characterization of Original 10-Stage and 7-Stage Modified Berner Type Impactors

Two cascade impactors, a Berner Low Pressure Impactor (BLPI model 25/0.018) and a modified BLPI (with a lower pressure drop) were characterized experimentally. First, the critical dimensions of each impactor stage that affect the collection characteristics were measured. Second, the absolute pressures at each stage were determined. Finally, the collection efficiency curves were obtained for all stages in a range of particle sizes from 0.026–13.7 μm. The collection efficiency of the modified impactor was measured using two condensation particle counters (CPC). Monodisperse calibration particles in the submicron size range were generated with a differential mobility analyzer (DMA). A vibrating orifice aerosol generator (VOAG) was used to produce supermicron test particles. In addition, the particle losses of both impactors were experimentally tested using ammonium sulfate particles under dry (15% RH) and wet (>80% RH) conditions. The losses were determined by rinsing a sampling foil and the corresponding impactor stage (nozzle plate, walls and spacer ring) with deionized water. Subsequently, the ammonium sulfate contents of the samples, along with the rinse water, were analyzed using ion chromatography.

Experiments on thermodiffusiophoresis of droplets in gaseous mixtures

Experiments on thermodiffusiophoresis of dioctylphthalate (DOP) droplets, generated by homogeneous nucleation and growing in different gaseous mixtures of DOP vapour with helium and hydrogen were carried out using a static thermal diffusion cloud chamber. The experiments were compared with theoretical predictions based on the formula of thermodiffusiophoresis by Viehland and Mason [J. Aerosol Sci., 8 (1977) 381]. An attempt has been also made to include the effect of thermal conductivity of DOP droplets, using the formula for thermophoretic velocity proposed by Talbot et al. [J. Fluid Mech., 101 (1980) 737]. Both approaches gave comparable results at higher pressures of inert gases. At lower pressures, a stronger influence of thermodiffusiophoretic effects than predicted has been observed.

Matrix effects in PIXE analysis of aerosols and ashes.

A comparison of instrumental neutron activation analysis (INAA) and proton-induced X-ray emission (PIXE) results for sizefractionated atmospheric aerosols (“coarse” and “fine” fractions with an equivalent aerodynamic diameter of 2–10 Μm and < 2 Μm, respectively, or the PM10 fraction) showed that PIXE yielded significantly lower results for the PM10 and coarse fractions, especially for elements with a low Z resulting from a particle size effect. Somewhat lower PIXE results were also obtained for the fine fraction of atmospheric aerosols. A correction is also needed for irregularly shaped deposits of combustion aerosols collected by a cascade impactor in 11 size fractions ranging from 0.016 to 14.3 Μm, as well as for thick samples of fly and bottom ashes. An equivalent layer thickness (ELT) model is proposed to correct the matrix effects in PIXE. The approaches for the calculation of ELT using a comparison of PIXE and INAA results or by comparing PIXE results obtained using two different incident proton beam energies (1.31 and 2.35 MeV) are described. The correction for the ash pellets and irregular deposits are also discussed.