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Analysis of number size distributions of tropical free tropospheric aerosol particles observed at Pico Espejo (4765 m a.s.l.), Venezuela

by T. Schmeissner, R. Krejci, J. Ström, W. Birmili, A. Wiedensohler, G. Hochschild, J. Gross, P. Hoffmann, S. Calderon show all authors
Atmospheric Chemistry and Physics ()
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The first long-term measurements of aerosol num- ber and size distributions in South-American tropical free troposphere (FT) were performed from March 2007 until March 2009. The measurements took place at the high al- titude Atmospheric Research Station Alexander von Hum- boldt. The station is located on top of the Sierra Nevada mountain ridge at 4765ma.s.l. nearby the city of M´ erida, Venezuela. Aerosol size distribution and number concentra- tion data was obtained with a custom-built Differential Mo- bility Particle Sizer (DMPS) system and a Condensational Particle Counter (CPC). The analysis of the annual and diur- nal variability of the tropical FT aerosol focused mainly on possible links to the atmospheric general circulation in the tropics. Considerable annual and diurnal cycles of the parti- cle number concentration were observed. Highest total par- ticle number concentrations were measured during the dry season (January–March, 519±613cm−3), lowest during the wet season (July–September, 318±194cm−3). The more humid FT (relative humidity (RH) range 50–95%) contained generally higher aerosol particle number concentrations (573±768cm−3 during dry season, 320±195cm−3 during wet season) than the dry FT (RH<50 %, 454±332cm−3 during dry season, 275±172cm−3 during wet season), in- dicating the importance of convection for aerosol distribu- tions in the tropical FT. The diurnal cycle in the variability of the particle number concentrationwas mainly driven by local orography. Correspondence

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