Clouds and aerosols in Puerto Rico - a new evaluation

• Published in: Atmospheric chemistry and physics discussions 2007-08, Vol.7 (4), p.12573-12616
• Main Authors: Allan, J D, Baumgardner, D, Raga, G B, Mayol-Bracero, O L, Morales-Garcia, F, Garcia-Garcia, F, Montero-Martinez, G, Borrmann, S, Schneider, J, Mertes, S, Walter, S, Gysel, M, Dusek, U, Frank, G P, Kraemer, M
• Format: Article
• Language: English
• Subjects: Ocean, Atmosphere; Sciences of the Universe
• ISSN: 1680-7367; 1680-7375

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements using some of the latest developments in online instrumentation took place in December 2004 in Puerto Rico. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape San Juan in the north-eastern corner of the island and at the top of East Peak mountain (1040 m a.s.l.), the two sites separated by 17 km. Additional measurements of the cloud droplet residual and interstitial aerosol properties were made at the mountain site, accompanied by measurements of cloud droplet size distributions, liquid water content and the chemical composition of cloud and rain water samples. Both aerosol composition and cloud properties were found to be sensitive to wind sector. Air from the east-northeast (ENE) was mostly free of anthropogenic influences, the submircron fraction being mainly composed of non-sea salt sulphate, while that from the east-southeast (ESE) was found to be moderately influenced by populated islands upwind, adding smaller (