Changes in rainwater composition in Wilmington, NC during tropical storm Ernesto

Abstract

Tropical weather events can contribute large wet depositional fluxes of biogeochemically important rainwater constituents over relatively short time periods. One composite sample during these events does not capture the dynamic nature of rainwater composition and can lead to misinterpretation of the impact of tropical events on local aquatic systems. Eight sequential samples were collected at 2–3 h intervals in Wilmington, NC during the duration of tropical storm Ernesto to examine a suite of rainwater constituents influenced by gas phase, aerosol, or mixed sources in the atmosphere. Real time wind speed and air mass back trajectories were used to examine the progression of the storm. Hydrogen peroxide and nitrate displayed washout trends during the storm. Dissolved organic carbon (DOC), hydrogen ion (H +), and total mercury (HgT) displayed washout at the beginning of the storm but toward the end of the storm concentrations increased, which corresponded to a shift in air masses from marine to terrestrial, increased ground air mass influence, and increased wind speeds. Integrated fluorescence, a measure of the chromophoric properties of the DOC, was highest at the beginning of the storm and than decreased but unlike DOC, the fluorescence did not increase at the end of the storm, indicating a change in the DOC source and composition during the storm. Chloride and sulfate, which are strongly influenced by seasalt aerosols, increased with increasing wind speeds. Factors such as wind speed, storm trajectory, and rainwater volume influenced rainwater constituent concentrations; the relative importance of these factors was a function of the sources of these rainwater constituents in rainwater.