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

In an effort to investigate the influence of different atmospheric flow patterns on the composition of precipitation on the island of Bermuda, a cluster analysis of atmospheric trajectories was performed to identify periods of similar transport. The cluster analysis technique represents a relatively objective alternative to the more subjective method of classifying 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 nitrate occurred in the warm season on Bermuda. There was no significant difference in the per event precipitation amount between seasons; however, there was significantly higher per event deposition of warm season non-seasalt sulfate, and nitrate. Significant differences in precipitation composition were also identified between flow patterns. It was found that the source regions which contributed the largest fraction of hydrogen ion deposition and nonseasalt sulfate deposition on Bermuda differed by season. During the cool months, 40% of the deposition occurred with transport from the west, off the East Coast of the US, implicating anthropogenic sources. In the warm season, an equally large fraction of deposition was associated with flow from the Bahamas region, suggesting an oceanic source of biogenic sulfuras the precursor.