Trace elements over the North Atlantic Ocean: Sources and transport pathways.

摘要

The air/sea exchange of continental materials that occurs following long-range transport to the open oceans is geochemically significant, but the sources for most of these substances are not known with certainty. This dissertation focuses on developing graphical and statistical methods to identify sources and transport pathways of aerosol and then applying them to aerosol from over the North Atlantic Ocean. The data used here were collected for the Atmosphere/Ocean Chemistry Experiment (AEROCE). Of the four AEROCE sampling sites (Bermuda, Barbados, Izaña, and Mace Head), Bermuda and Mace Head are discussed intensively in this dissertation.; The graphical methods reveal important information visually and simply. By using this approach, the dry-depositional component of aerosol at Bermuda and Mace Head was determined semiquantitatively. Another type of plot was used to derive sources for aerosol and their compositions at Bermuda and Mace Head.; A method was developed to quantitatively evaluate how well factor analysis techniques can resolve sources for aerosol. It was found that to optimize the resolving power of FA, the most important consideration is to select a suite of elements that have few missing data and that represent individual sources unambiguously.; The graphical and factor analysis techniques, combined with other tools such as meteorological maps, were used to determine the sources and transport of aerosol at Bermuda and Mace Head. A detailed seasonal pattern of pollution (particulates and trace gases) at Bermuda, semiannual cycles with spring and fall maxima, was revealed to be closely linked with large-scale circulation over the North Atlantic Ocean. For aerosol at Mace Head, a sulfur-group factor was revealed to have two components: a (marine) background secondary aerosol and a pollution-derived secondary aerosol that most likely comes from coal combustion.; Compared to Bermuda, aerosol at Mace Head had stronger marine and SO ₄2−-Se sources but weaker crustal and residual-oil sources, and less-dramatic seasonal variation. The maximum transport of pollution was observed in summer months, with a peak in May, and was mostly associated with recirculation of westerlies passing over nearby land (Ireland, United Kingdom, and the Belgium-Netherlands-Luxemburg region).