The Azores Islands: A Unique Location for Ground-Based Measurements in the MBL and FT of the Central North Atlantic.

The Azores Islands - the only islands in the central North Atlantic that are distant from all surrounding continentes - have historically been important for studies of the North Atlantic atmosphere. Prior to the advent of satellite observations, they provided weather data critical to the accuracy of forecasts of European weather. Today, they provide a unique base for observations of the impacts on atmospheric composition of emissions from the surrounding continents. As part of the NARE program, ground-based measurements of CO and O3 [Parrish et al., 1998] and NOY [Peterson et al., 1998], as well as ozone sondes [Oltmans et al., 1996] were made in 1993 on the island of Terceira. The Azores have also served as a base for airborne studies (e.g., those described by Law et al., this issue) and shipboard studies [e.g., Huebert et al., 1996]. Here, we briefly discuss Azores ground-based measurements, with an emphasis on a new mountaintop site designed to probe the free troposphere. […]