Ion-induced Nucleation Research Articles

Experimental studies of the ion-induced binary nucleation

We have conducted an experimental investigation of the aerosol nucleation phenomenon in a binary mixture of H 2O and H 2SO 4 vapors in a carrier stream of N 2 gas in the presence of ions produced by a low energy beta source. The H 2O vapor pressure in the reaction cell ranged from 0.6 to 7.5 torr, whereas the H 2SO 4 vapor pressure was varied from 1.6 × 10 −9 to 2 × 10 −7 torr. The temperature in the reaction cell ranged from 308 to 330K. The first series of experiments were conducted at a reaction cell pressure of ∼ 250 torr. Based on the cluster masses measured with a quadrupole mass spectrometer, cluster spectra of the form (H 2SO 4) m H + were identified. The number of H 2SO 4 molecules in the clusters ranged from 0 to 6 whereas the number of H 2O molecules ranged from 1 to 20 depending on the concentration of H 2SO 4 and H 2O vapors in the reaction chamber. The experimental system was then modified to minimize the possible fractionation effects by reducing the cell pressure to ∼ 20 torr and eliminating the space between the reaction cell and the collimator leading to the quadrupole mass spectrometer. The results of these measurements are discussed.

Experimental studies of ion clustering: relationship to aerosol formation processes and some atmospheric implications

Studies of the clustering of molecules about ions are of both fundamental and practical interest. The results find immediate application in assessing the validity of classical expressions for nucleation phenomenon and provide a basis for further developments of nucleation theory. It is well known that the atmosphere contains substantial ion populations and their potential role in aerosol formation provides a strong coupling between the fields of atmospheric electricity and other areas of the atmospheric sciences. As a result of recent advances in high pressure mass spectrometry, the detailed processes involved in the continuous transition of a system from the gaseous to the condensed (aerosol) state can be investigated at the molecular level. Many of the recent findings in ion clustering are reported in literature devoted to fundamental chemistry and physics and are not in a form of immediate value to the researcher in the field of aerosol science. The purpose of this paper is to review recent progress in understanding ion clustering as it relates to the general mechanisms of gas-to-particle conversion. Laboratory data on the bonding of various negative and positive ion complexes is used to assess the validity of the classical model to ion-induced nucleation. Further consideration is given to the role of ion cluster-ion cluster interaction in aerosol formation.

Theoretical Prediction of Ion Clusters Relevant to the Atmosphere: Size and Mobility

Abstract The clustering of water vapor about ions is important because of its relevance to atmospheric electrical processes. For this reason we have placed our emphasis particularly on the description of the size distribution (concentrations) and mobilities of the small ion clusters at various humidities. From our present theoretical study, we find that most of the hydronium ions H3O+ tend to associate with a small number of water molecules to form a hydrated ion cluster even at extremely low humidities in the range of 5 × 10−3 to 1%. At atmospherically more realistic humidities and at the room temperature, our computed number of water molecules in the hydrated ion clusters is predicted to be relatively small. It is then conjectured that ion-induced nucleation process (if it occurs) starts rather from the small hydrated ion clusters which initially existed even at extremely low humidities in the atmosphere. In addition, we also find that, in general, the hydrated ion clusters of small sizes corresponding ...

Ion-induced nucleation of atmospheric water vapor at the mesopause

The possibility of aerosol formation at the mesopause by ion-induced water vapor nucleation is investigated. A simple kinetic model considering new information on ion-growth and -recombination processes as well as on mesospheric water vapor and temperatures is put forward. It predicts ion-nucleation to be possible only at high latitudes during local summer in a narrow height region, extending from about 88 to 91 km. Derived nucleation rates increase steeply with decreasing temperatures and electron number densities. If for the latter typical values are considered nucleation rates may become sufficiently high to account for the observed mesospheric aerosol layer. Various observed characteristic temporal and spatial variations of the aerosol layer including its response to geomagnetic activity may be explained by the model.

The formation of ultrafine ion H 2O— H 2SO 4 aerosol particles through ion-induced nucleation process in the stratosphere

In this theory, we have demonstrated that ultrafine (ångstrom size) prenucleation ion clusters comprise a segment of the overall nucleation size spectrum in the stratosphere. Also, the ion clusters exist in a spectrum attributable to certain favorable physical states. The distribution changes when the temperature and ambient water and sulfuric acid vapor pressures vary with altitude. Around 18 km, the spectrum of prenucleation embryo radii are in the range of 6.3 to 7.2 Å. It is also observed that the average radius of the ion cluster spectrum decreases with altitude, while the weight percentage of sulfuric acid in the average ion cluster increases with altitude. A profile for the ion cluster spectrum and its variation with altitude is constructed. Under stratospheric conditions, growth to large aerosols by nucleation is negligible. A comparison of the characteristic interaction time for an ion-molecule reaction with that of an ion annihilation and recombination shows that ion nucleation is the favored process in forming ultrafine background aerosols. So prenucleation ion clusters will take the place of primary ions as the main participant in the ion recombination, ion annihilation, coagulation and condensation processes.

The formation of ultrafine ion H 2OH 2SO 4 aerosol particles through ion-induced nucleation process in the stratosphere : By L. Y. Chain and V. A. Mohnen, Atmospheric Sciences Research Center, State University of New York, Albany, NY 12222, U.S.A.

The formation of ultrafine ion H 2OH 2SO 4 aerosol particles through ion-induced nucleation process in the stratosphere : By L. Y. Chain and V. A. Mohnen, Atmospheric Sciences Research Center, State University of New York, Albany, NY 12222, U.S.A.

Theory of the formation of aerosols of volatile binary solutions through the ion-induced nucleation process

The classical Thomson's theory is modified to study the formation of aerosols through the nucleation of a binary mixture of vapors and in the presence of ion sources. Analytical expressions for estimating the critical size and composition of droplets formed through the ion-induced nucleation process are derived. Conclusions drawn from this study agree qualitatively with the available experimental results.

On the characteristics of sulfate aerosols formed in the presence of ion sources

The general theory of ion-induced nucleation is applied to a study of the formation of sulfate aerosols in the presence of ion sources. It is shown that these aerosols can be divided into three categories: stable, transitory and unstable according to the environmental conditions in which they are formed. Graphical methods are presented so that the critical size and composition of ion-induced sulfate aerosols at 25°C for different ambient conditions can be quickly estimated. Our results are in good agreement with calculations assuming discrete numbers of molecules in the aerosol. The general characteristics of these aerosols are also discussed.