J. Boulon

Observations of nucleation of new particles in a volcanic plume

Volcanic eruptions caused major weather and climatic changes on timescales ranging from hours to centuries in the past. Volcanic particles are injected in the atmosphere both as primary particles rapidly deposited due to their large sizes on time scales of minutes to a few weeks in the troposphere, and secondary particles mainly derived from the oxidation of sulfur dioxide. These particles are responsible for the atmospheric cooling observed at both regional and global scales following large volcanic eruptions. However, large condensational sinks due to preexisting particles within the plume, and unknown nucleation mechanisms under these circumstances make the assumption of new secondary particle formation still uncertain because the phenomenon has never been observed in a volcanic plume. In this work, we report the first observation of nucleation and new secondary particle formation events in a volcanic plume. These measurements were performed at the puy de Dôme atmospheric research station in central France during the Eyjafjallajokull volcano eruption in Spring 2010. We show that the nucleation is indeed linked to exceptionally high concentrations of sulfuric acid and present an unusual high particle formation rate. In addition we demonstrate that the binary H2SO4 - H2O nucleation scheme, as it is usually considered in modeling studies, underestimates by 7 to 8 orders of magnitude the observed particle formation rate and, therefore, should not be applied in tropospheric conditions. These results may help to revisit all past simulations of the impact of volcanic eruptions on climate.

Sub-3 nm Particles Detection in a Large Photoreactor Background: Possible Implications for New Particles Formation Studies in a Smog Chamber

New particles formation experiments have been conducted in the experimental multiphasic atmospheric simulation chamber (CESAM) smog chamber. The nucleation events generated during the dark ozonolysis of sabinene were monitored using a neutral cluster and air ions spectrometer in the size range 0.8–42 nm under simulated atmospheric conditions. The measurements show that a significant amount of pre-existing clusters exist in the 1–2 nm size range even in very clean controlled conditions. Numerical modeling experiments indicate that a range of 9–67% of pre-existing clusters can explain, through activation by organic vapors, the number of new particles formed when sabinene is oxidized, with an increasing contributing fraction for increasing condensable vapor concentrations. These findings suggest that atmospheric simulation chambers backgrounds have to be carefully characterized for their sub-3-nm neutral cluster concentration content before nucleation parameterizations can be derived. Copyright 2013 American Association for Aerosol Research

DOUBLE FIT: Optimization procedure applied to lattice strain model

Modeling trace element partition coefficients using the lattice strain model is a powerful tool for understanding the effects of P-T conditions and mineral and melt compositions on partition coefficients, thus significantly advancing the geochemical studies of trace element distributions in nature. In this model, partition coefficients describe the strain caused by a volume change upon cation substitution in the crystal lattice. In some mantle minerals, divalent, trivalent, and tetravalent trace element cations are mainly substituted in one specific site. Lattice strain model parameters, for instance in olivine and plagioclase, are thus fit for one crystal site. However, trace element cations can be substituted in two sites in the cases of pyroxenes, garnets, amphiboles, micas, or epidote-group minerals. To thoroughly study element partitioning in those minerals, one must consider the lattice strain parameters of the two sites. In this paper, we present a user-friendly executable program, working on PC, Linux, and Macintosh, to fit a lattice strain model by an error-weighted differential-evolution-constrained algorithm (Storn, R., and Price, K. 1997. Differential evolution - A simple and efficient heuristic for global optimization over continuous spaces. Journal of Global Optimization 11, 341–359). This optimization procedure is called DOUBLE FIT and is available for download on http://celiadalou.wixsite.com/website/double-fit-program. DOUBLE FIT generates single or double parabolas fitting experimentally determined trace element partition coefficients using a very limited amount of data (at minimum six experimental data points) and accounting for data uncertainties. It is the fastest calculation available to obtain the best-fit lattice strain parameters while accounting for the elastic response of two different sites to trace element substitution in various minerals.