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 continue operating primary field sites at Tudor Hill, Bermuda and Mace Head, Ireland. AEROCE primary sites are and will continue to be state-of-the-art atmospheric sampling facilities which support a wide range of atmospheric chemistry measurements. Aerosol, gas and precipitation samples are collected at these sites in accordance with protocols described in the AEROCE Overview. The Facilities at each site include a walk-up tower, a chemical clean laboratory with two laminar flow clean hoods, an instrument laboratory and sampling equipment shelters. Sampling equipment for aerosol and precipitation samples are mounted on the towers and are controlled by automatic control systems. Analytical instruments that measure ozone are housed in the instrument laboratory. A full-time on-site technician operates each site. The PNOG receives site data and aerosol samples from the field sites and redistributes the materials as required by AEROCE investigators.