Theoretical atmospheric chemistry models used to predict the effects of human activities on stratospheric ozone are dependent on measurement of reactive chemical species in the upper atmosphere. The radical OH is an important chemically active transient species that is believed to control the concentration of ozone above 40 km, and to have a strong influence on the partitioning of odd-nitrogen and odd-chlorine species that affect the main ozone level at about 25 km altitude. A relatively inexpensive method of gaining information about fluctuations in OH levels is provided by ground-based observations of the column abundance of OH by the PEPSIOS (Poly Etalcon Pressure Scanned Interferometric Spectrometer) system. Under previous NSF grants the principal investigator has carried on a successful program of PEPSIOS measurements at the Fritz Peak Observatory in Colorado Since 1977, and more recently for Boca Raton, Florida, the Poker Flat Research Range near Fairbanks, Alaska, and at Truk Island in Micronesia. This research is being done by a scientist who is generally recognized as a pioneer in this area of atmospheric chemistry research. His research papers on the spatial and temporal variations in the stratospheric hydroxyl radical concentrations are widely acclaimed and have provided important information about several aspects of the chemistry of the stratosphere and mesosphere. This continuation research will include continued studies of the middle atmosphere hydroxyl radical in the tropics as well as the measurement of this species from the Fritz Peak Observatory.
