NSF Award
0342548
This project is a component of the broader "Rain in Cumulus Over the Ocean" (RICO) experiment, a multi-investigator study of warm-rain formation and the characteristics of trade-wind Cumuli to be conducted in Antigua-Barbuda in 2004-2005. Rain in such clouds forms after condensation on particles called "cloud condensation nuclei," or CCN, some of which are thought to be partly composed of organic compounds. However, little is known about the organic components in CCN, and this is a controversial topic because standard CCN measurements may not provide valid measurements in cases where there is a substantial organic component. The objective of this research project is to determine representative concentrations, size distributions, composition, CCN activity, and organic fraction for tropical marine aerosols, with particular attention to the influence of organic aerosols on the properties of clouds. Filter samples will be collected at three sites, two in Puerto Rico and one at Barbuda near the RICO experimental area, so that natural and anthropogenic sources can be separated. Analyses of the collected samples will be performed by an international collaboration of chemists who will be participating in this work. Other components of the study include measurement of the fraction of particles scavenged by clouds and study of possible effects of water-soluble organic carbon on the surface tension of solution droplets.<br/><br/>The project has the potential to help determine if organic constituents have a significant influence on CCN, the subset of particles that determines the droplet concentration and droplet size in tropical clouds. Understanding the influence of such particles on clouds is a key contribution to RICO because the sizes of the droplets that result influence the rate and efficiency of precipitation from the clouds, the primary processes being studied by that experiment. The results have far-ranging potential implications in studies of anthropogenic influences on climate because they advance understanding of the effects of particles, including those produced by humans or those associated with air pollution, on rainfall. The project also brings good local involvement into the RICO experiment (to be conducted in Antigua-Barbuda) by including investigators and students from the University of Puerto Rico. A Graduate Student seminar conducted during the field experiment will provide educational opportunities for students from this university and others and will help advance training in this area, with particular benefits for the predominantly Hispanic students at this university. New equipment to be acquired for this work will also enable related studies to continue at this institution.
