Speciation of water-soluble inorganic, organic, and total nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles

Cloud water, rainwater, and aerosol particles were collected in Puerto Rico from December 2004 to March 2007 in order to investigate their chemical composition, relation to sources, and removal processes. The species analyzed were inorganic ions, metals, total and dissolved organic carbon (TOC, DOC), total nitrogen (TN), and organic acids. For all samples, the dominant species were marine (Na+, Cl-), representing about 50%-65% of total content. Non-sea-salt fraction was dominated by SO42- (17%-25%), followed by water-soluble organic (2%-8%) and total nitrogen (2% -6%) compounds. Organic acids represented contributions to the organic fraction in cloud water of 20% and 6% for aerosol particles. Inorganic species were predominant in total nitrogen portion. The chemical composition of cloud water, rainwater, and aerosol particles were observed to be sensitive to transport patterns. Air masses from northwest Africa showed the highest concentrations of nss-Ca2+, Fe, and Al, suggesting a crustal origin. The pH values for cloud water and rainwater observed under this transport pattern were higher than background conditions, probably due to the alkalinity associated with nss-Ca2+. The highest concentrations of Cl- and SO42-, with lower pH, were measured during periods of influence from Soufriere Hills volcano eruptions, most likely due to emitted SO2 and HCl. Air masses from North America had an anthropogenic influence, where levels of nss-SO42-, TOC, and TN were higher (similar to 4 times) than in clean air masses. These results suggest that long-range transport could be an extra source of metals and organic/nitrogen species to the Caribbean region ecosystems.