References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-11-3319-2011

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

Schmeissner

¹ Krejci

² Ström

² ³ Birmili

¹ Wiedensohler

¹ Hochschild

⁴ Gross

⁴ Hoffmann

⁵ Calderon

⁵

Leibniz Institute for Tropospheric Research e.V. (IfT), 04318 Leipzig, Germany

Stockholm University, Department of Environmental Science (ITM), 106 91 Stockholm, Sweden

Norwegian Polar Institute (NPI), 9296 Tromso, Norway

Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research (ASF), 76344 Eggenstein-Leopoldshafen, Germany

Universidad de Los Andes, Merida 5101, Venezuela

07 04 2011

11 7 3319 3332

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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The first long-term measurements of aerosol number 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 altitude Atmospheric Research Station Alexander von Humboldt. The station is located on top of the Sierra Nevada mountain ridge at 4765 m a.s.l. nearby the city of Mérida, Venezuela. Aerosol size distribution and number concentration data was obtained with a custom-built Differential Mobility Particle Sizer (DMPS) system and a Condensational Particle Counter (CPC). The analysis of the annual and diurnal 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 particle number concentration were observed. Highest total particle number concentrations were measured during the dry season (January–March, 519 ± 613 cm−3), lowest during the wet season (July–September, 318 ± 194 cm−3). The more humid FT (relative humidity (RH) range 50–95 %) contained generally higher aerosol particle number concentrations (573 ± 768 cm−3 during dry season, 320 ± 195 cm−3 during wet season) than the dry FT (RH < 50 %, 454 ± 332 cm−3 during dry season, 275 ± 172 cm−3 during wet season), indicating the importance of convection for aerosol distributions in the tropical FT. The diurnal cycle in the variability of the particle number concentration was mainly driven by local orography.

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