Vladimír Ždímal

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.

Homogeneous nucleation rates of n-pentanol measured in an upward thermal diffusion cloud chamber

Homogeneous nucleation rates of n-pentanol as functions of both supersaturation and temperature were measured in two different upward thermal diffusion cloud chambers, by research groups in Prague and Baltimore. The measurements were made at temperatures between 280 K and 320 K. The nucleation rates obtained are compared to the rates measured by Luijten et al. [J. Chem. Phys. 106, 4152 (1997)], by Hrubý et al. [J. Chem. Phys. 104, 5181 (1996)], and by Strey et al. [J. Chem. Phys. 84, 2325 (1986)]. Fair agreement between our data and the data obtained by the other authors also was found.

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

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.

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

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.

Homogeneous nucleation rate measurements in supersaturated water vapor II

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.

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.

Detailed comparison of OC/EC aerosol at an urban and a rural Czech background site during summer and winter

Winter and summer measurements of organic carbon and elemental carbon (OC and EC) in PM2.5 were performed in parallel at two sites, the rural background station Košetice and the Prague-Suchdol urban background site, with a 2-h time resolution using semi-online field OC/EC analysers. Seasonal and site differences were found in the OC and EC contents of PM2.5. Overall, the highest concentrations of both OC and EC were during winter at the urban site. The average urban impact was 50% for OC and 70% for EC. The summer season gives similar concentrations of OC at both sites. However, higher concentrations of EC, caused by higher traffic, were found at the urban site with an average urban increase of 50%. Moreover, an analysis of four OC fractions depending on the volatility (OC1 - most volatile, OC4 - least volatile) and pyrolytic carbon (PC) is provided. A similar level of each OC fraction at both sites was found in summer, except for higher OC1 at urban and higher PC at the rural site. In winter, the differences between the urban and rural sites were dominated by a large increase of the OC1 fraction in comparison with the rural site. A diurnal pattern of concentration and share of OC1 and PC suggests a prevailing influence of local sources on their concentrations at the urban site in winter. The OC3 and OC4 diurnal cycles suggest their more regional or long range transport origin in both seasons. The prevalent influence of OC1 at any urban site has not been previously reported. The minimisation of semi-volatile carbon losses during semi-continuous sampling and analysis, in comparison with off-line sampling methods, is a probable reason for the observed differences.

The homogeneous nucleation of 1-pentanol in a laminar flow diffusion chamber: The effect of pressure and kind of carrier gas

The influence of total pressure and kind of carrier gas on homogeneous nucleation rates of 1-pentanol was investigated using experimental method of laminar flow diffusion chamber in this study. Two different carrier gases (helium and argon) were used in the total pressure range from 50 to 400 kPa. Nucleation temperatures ranged from 265 to 290 K for 1-pentanol-helium and from 265 to 285 K for 1-pentanol-argon. Nucleation rates varied between 10(1) and 10(6) cm(-3) s(-1) for 1-pentanol-helium and between 10(2) and 10(5) cm(-3) s(-1) for 1-pentanol-argon. Both positive and slight negative pressure effects were observed depending on temperature and carrier gas. The trend of pressure effect was found similar for both carrier gases. Error analysis on thermodynamic properties was conducted, and the lowering of surface tension due to adsorption of argon on nucleated droplets was estimated. A quantitative overview of pressure effect is provided.

Mass and chemically speciated size distribution of Prague aerosol using an aerosol dryer--the influence of air mass origin.

Ambient aerosol particles dried using a diffusional aerosol dryer were sampled using a 7-stage modified Berner low pressure impactor with a back-up filter during the heating and non-heating season campaigns in 2008. The samples were analyzed for water-soluble ions and water-soluble organic carbon. Because of the drying, the aerosol size distribution was not influenced by the daily variability of ambient relative humidity. The results summarize the observations from campaigns in both the heating (11 sampling days) and non-heating (10 sampling days) seasons. The aerosols sampled on individual days were classified based on the connected air mass back trajectories into three classes: sea-influenced aerosol (SIA), continental aerosol (CA) and mixed aerosol (MA) for samples of intermediate origin. The differences between CA and SIA were substantial both when looking at the normalized mass size distributions of the particulate matter (PM) and of the individual species and when taking into account the absolute concentrations in the fine and coarse size fractions. The main differences were found in the normalized mass size distributions of the PM and of the sea-salt related ions.