Atmos. Chem. Phys. Discuss., 11, 8249-8290, 2011
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Investigation of nucleation events vertical extent: a long term study at two different altitude sites
J. Boulon1, K. Sellegri1, M. Hervo1, D. Picard1, J.-M. Pichon1, P. Freville1, and P. Laj2
1Laboratoire de Météorologie Physique CNRS UMR 6016, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, France
2Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS UMR5183, Saint Martin d'Héres, France

Abstract. In this work we present an analysis of the occurrence of nucleation events during more than three years of measurements at two different rural altitude sites, the puy de Dôme research station (1465 m a.s.l.) and the Opme station (660 m a.s.l.), central France. The collected database is a unique combination of a Scanning Mobility Particle Sizer (SMPS, 10–400 nm) measurements, an air ion spectrometers (AIS, 0.5 to 45 nm) and neutral clusters and air ion spectrometers (NAIS, 0.5 to 45 nm) measurements at two different altitudes nearly located research stations, from February 2007 to June 2010. During the measurement period, neither the particle formation rates (J2 = 1.382 ± 0.195 s−1) nor the growth rates (GR1.3–20 nm = 6.20 ± 0.12 nm h−1) differ from one site to the other on average. Hovewer, we found that, on 437 sampling days in common to the two sites, the nucleation frequency was higher at the puy de Dôme station (35.9%, 157 days) than at the low elevation station of Opme (20.8%, 91 days). The role of sulfuric acid in the nucleation process was investigated at the altitude station and no correlation was found between nucleation events and the estimated sulfuric acid concentrations. Nevertheless, the contribution of ion-induced nucleation was found to be relatively high (12.49 ± 2.03% of the total nucleation rate). LIDAR measurements and the evolution of the potential equivalent temperature revealed that the nucleation could be triggered either (i) within the whole low tropospheric column at the same time from the planetary boundary layer to the top of the injection layer (29.2%, 47 events), (ii) above the planetary boundary layer upper limit (43.5%, 70 events), and (iii) at low altitude and then transported, conserving dynamic and properties, at high altitude (24.8%, 40 events). This is the first time that the vertical extent of nucleation can be studied over a long observational period, allowing for a rigorous statistical analysis of the occurrence of nucleation over the whole lower troposphere. This work highlights the fact that nucleation can have occur over a large vertical extent, at least the whole low tropospheric column, and also the fact that it occurs twice as frequently as actually detected in the planetary boundary layer.

Citation: Boulon, J., Sellegri, K., Hervo, M., Picard, D., Pichon, J.-M., Freville, P., and Laj, P.: Investigation of nucleation events vertical extent: a long term study at two different altitude sites, Atmos. Chem. Phys. Discuss., 11, 8249-8290, doi:10.5194/acpd-11-8249-2011, 2011.
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