Quantifying the relationship between atmospheric transport and the chemical composition of precipitation on Bermuda

Abstract

In an effort to investigate the influence of different atmospheric flow patterns on thecomposition of precipitation on the island of Bermuda, a cluster analysis of atmospherictrajectories was performed to identify periods of similar transport. The cluster analysistechnique represents a relatively objective alternative to the more subjective method ofclassifying trajectories according to compass sector. Data were stratified into two broadseasons, defined as a warm (April-September) and a cool (October-March) season. Relative tothe cool season, significantly higher per event concentrations of non-seasalt sulfate and nitrateoccurred in the warm season on Bermuda. There was no significant difference in the per eventprecipitation amount between seasons; however, there was significantly higher per eventdeposition of warm season non-seasalt sulfate, and nitrate. Significant differences inprecipitation composition were also identified between flow patterns. It was found that thesource regions which contributed the largest fraction of hydrogen ion deposition and nonseasaltsulfate deposition on Bermuda differed by season. During the cool months, 40% of thedeposition occurred with transport from the west, off the East Coast of the US, implicatinganthropogenic sources. In the warm season, an equally large fraction of deposition wasassociated with flow from the Bahamas region, suggesting an oceanic source of biogenic sulfuras the precursor. DOI: 10.1111/j.1600-0889.1988.tb00117.x