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. The AEROCE Primary Network Operations Group (PNOG) is located at the Center for Atmospheric Chemistry Studies, Graduate School of Oceanography, University of Rhode Island. This group will establish Primary Network sites in the North Atlantic Ocean at the following locations: Daniels Head, Bermuda; Mace Head, Ireland; Ragged Point, Barbados; and Izania, Tenerife. These sites will be high quality state-of-the-art atmospheric sampling stations with facilities to support a wide range of atmospheric chemistry measurements. Aerosol, gas, and precipitation samples will be collected at these sites and will follow the sampling protocol as outlined in the AEROCE Overview. The PNOG will construct and operate the sampling stations. Each station will have a triplet rain collector and six aerosol/trace gas collection systems for obtaining continuous daily grab samples. Flask samples for certain trace gases will also be collected twice a week. Other gases analyzed by on-site techniques will have essentially a continuous record. The group will have an on-site technician with technical expertise at each site. The group will receive samples and data from the Primary Network stations and will redistribute the materials as required by AEROCE investigators. The Bermuda-West (Daniels Head) site will be operational in August, 1988 and the Mace Head, Ireland site will be operational in May, 1988.