Ion-induced Nucleation Process Research Articles

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

Abstract. New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over South America (January–March 2005), Australia (November–December 2005), West Africa (August 2006) and Central America (2004–2007). Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different dp50 (50% lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 Geophysica in the altitude range of 12.0–20.5 km and on board the DLR Falcon-20 at up to 11.5 km altitude. On board the NASA WB-57F size distributions were measured over Central America in the 4 to 1000 nm diameter range with a system of nucleation mode aerosol spectrometers. Nucleation mode particle concentrations (NNM) were derived from these measurements which allow for identifying many NPF events with NNM in the range of thousands of particles per cm3. Over Australia and West Africa, we identified NPF in the outflow of tropical convection, in particular of a Mesoscale Convective System (MCS). Newly formed particles with NNM > 1000 cm−3 were found to coexist with ice cloud particles (dp > 2 μm) as long as cloud particle concentrations remained below 2 cm−3. The occurrence of NPF within the upper troposphere and the TTL was generally confined within 340 K to 380 K potential temperature, but NPF was of particular strength between 350 K and 370 K (i.e. ~1–4 km below the cold point tropopause). Analyses of the aerosol volatility (at 250 °C) show that in the TTL on average 75–90% of the particles were volatile, compared to typically only 50% in the extra-tropical UT, indicative for the particles to mainly consist of H2SO4-H2O and possibly organic compounds. Along two flight segments over Central and South America (24 February 2005 and 7 August 2006, at 12.5 km altitude) in cloud free air, above thin cirrus, particularly high NNM were observed. Recent lifting had influenced the probed air masses, and NNM reached up to 16 000 particles cm−3 (ambient concentration). A sensitivity study using an aerosol model, which includes neutral and ion induced nucleation processes, simulates NNM in reasonable agreement with the in situ observations of clear-air NPF. Based on new, stringent multi-CPC criteria, our measurements corroborate the hypothesis that the tropical UT and the TTL are regions supplying freshly nucleated particles. Our findings narrow the altitude of the main source region to the bottom TTL, i.e. to the level of main tropical convection outflow, and, by means of measurements of carbon monoxide, they indicate the importance of anthropogenic emissions in NPF. After growth and/or coalescence the nucleation mode particles may act as cloud condensation nuclei in the tropical UT, or, upon ascent into the stratosphere, contribute to maintain the stratospheric background aerosol.

Clusters: a bridge across the disciplines of environment, materials science, and biology.

The formation of finite particles and dust grains in interstellar media, heterogeneous reactions occuring in the stratosphere, and unidentified infrared bands in interstellar gas clouds have been suggested to have a cluster origin. In the following, we provide examples where clusters have played a role in describing and accounting for phenomena in atmospheric science. ### Aerosols and Fine Particles. Fine particles are ubiquitous throughout the universe; they are present in interstellar media (e.g., in dense clouds where ion clustering reactions have been invoked in mechanisms responsible for the formation of molecules); they are ultimately responsible for the rings around Saturn; and, in some theories of planetary evolution, they are used to explain the origin of planets themselves. The fascinating issue of interstellar dust, which could serve as a supply of biotic raw material on earth, is also relevant for astrobiology. In high altitudes of our own planet, there are layers of meteoritic ablation where dust layers are known and noctilucent clouds form, possibly enhanced by ion-induced nucleation processes. For more “down-to-earth” reasons, fine particles are of interest to environmental scientists who must contend with them in ways more germane to our everyday life in terms of visibility and health (1–6). Clustering and related nucleation phenomena are, in part, responsible for their formation (7–13). For many years, the community of atmospheric scientists was divided into two groups: those dealing with problems of visibility effects, clouds, and condensation processes and those interested in chemical transformations. Many atmospheric chemists considered heterogeneous processes to be of secondary importance and of third-order interest; they usually attempted to account for most observed phenomena considering only gas-phase reactions. However, one need only realize that gas-phase acid molecules … †To whom correspondence may be addressed. E-mail: pjena{at}vcu.edu or awc{at}psu.edu

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 ...

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.