Over the past 10-15 years atmospheric chemistry has evolved from a young research discipline devoted primarily to local problems of urban pollution and air quality to a mature science concerned with the hemispheric to global scale cycling of a wide variety of chemical species. To a large extent this change has resulted from an increasing realization that human activities can cause chemical disturbances to the natural troposphere on scales far beyond local concerns. Well-known examples include changes in the regional-to-global concentrations of certain nitrogen compounds, lead and other heavy metals, artificial radionuclides, a number of synthetic organic substances, certain acid-forming species, carbon dioxide and methane. These chemical changes in the atmosphere can often extend to the earth's soils, oceans, and biota far from the original source region. They can result in alterations in the earth's climate, changes in vital nutrient cycles, and impact significantly on the public health and quality of life on earth. The Atmosphere/Ocean Chemistry Experiment (AEROCE) will be a coordinated multi-institutional atmospheric and marine chemistry research project centered in the North Atlantic region. The ultimate goal of the AEROCE project will be the development of a predictive capability for the continentally derived species observed in the marine troposphere over the North Atlantic. The selection of sites and the measurement protocol in AEROCE has been developed jointly by modelers and field experimentalists. This element of the AEROCE research project is designed to measure: (1) the concentration of 210Pb and 7Be in all aerosol samples collected as part of the standard AEROCE protocol at all sites, (2) the monthly deposition flux of 210Pb and 7Be to all sites and (3) the long term mean deposition rates of 137Cs and 210Pb to soils at a majority of the sites. These nuclides have well known sources and do not undergo chemical transformations. This research seeks to achieve 5 objectives: (1) The observed concentrations and deposition of these nuclides will be used to test and refine both event-oriented and climatological numerical models of atmospheric transport. (2) The correlations between the radionuclides and other species will be used to infer the sources of the other species and of seasonal changes in source or transport. (3) The ratio of deposition rate to surface air concentration will be used to quantify the efficiency of transfer of aerosols to the surface. (4) The 7Be/210Pb ratio will be developed as a measure of vertical mixing in the troposphere. (5) Comparison of 7Be/210Pb in air and deposition will help quantify both the absolute value and the vertical variation of these elements.
