Organic Carbon in Cloud Water and Aerosols from a Tropical Marine Environment

Chemical characterization was performed on cloud water and aerosol samples collected as part of the Rain In Cumulus over the Ocean Experiment (RICO) experiment, in a new intensive field campaign that took place in Puerto Rico from July to August 2006. The main objective of this study is to seek a better understanding of the impact of tropical marine aerosol on clouds and climate, with particular interest in the organic fraction. Cloud water samples were collected at the East Peak (EP) mountain site (1051 m.a.s.l), using a single-stage Caltech Active Strand Cloudwater Collector. Aerosol samples were collected in our reference site, Cabezas de San Juan (CSJ), using stacked-filter units with Teflon and quartz filters. Meteorological data were collected at both sites. pH measurements were performed in cloud water samples immediately after collection and before analyses. The analyses performed on both cloud and aerosol samples were total organic carbon (TOC analyzer, Shimadzu 5500) and thermal/optical analyses (EC/OC Analyzer, Sunset Lab.). Preliminary results showed an average pH of 5.8 for the cloud water samples. Concentrations of total organic carbon (TOC) and dissolved organic carbon (DOC) in cloud water samples were 1.8 ppmC and 0.3 ppmC, respectively. Particulate matter was visible in the cloud water samples and the content of total carbon (TC) obtained after filtration was on average 1 ug per mL. Back trajectories calculated with the NOAA HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) transport and dispersion model showed that the origin of the air masses was predominantly from the northeast (Atlantic Ocean and the northwest African coast). A more complete set of results that will include ion chromatography and total nitrogen analyses for aerosol and cloud water samples, the comparisons between the two sampling sites, more information about the concentrations of the carbonaceous species of interest (i.e., elemental carbon, total carbon, TOC, and DOC), and the relationship of our results to the origin of the air masses will be presented at the meeting.