Pacific Exploratory Mission (PEM-West A) aircraft ozone data and concurrently measured TOMS atmospheric total column ozone data are examined. The focus of the paper is to determine, for relatively remote Pacific regions (110¿--180 ¿E longitude, 0¿--40 ¿N latitude), what fraction of total column ozone can be attributed to lower-tropospheric ozone (surface to 9-km altitude) and how this fraction varies with time. At ≈30¿ to 40 ¿N the surface to 9-km ozone column contributes about 10% to total column ozone. Of this 10%, about half is attributed to the surface to 3-km column. Nearer the equator (0¿--15 ¿N), the contributions are less, about 5 (0--9 km) and 1% (0--3 km) of the total column, respectively. Variations in ozone within the 3-km and 9-km columns over periods of days tend to be larger at northern latitudes. At 40¿ to 50 ¿N, ozone variations within the columns can result in changes in each column's contribution to the total column that approach >50% of the column's contribution to the total column. Nearer the equator, variations are ≤1 Dobson unit which is generally <10% of the surface to 9-km column's contribution to total column ozone. The results provide insight into the relative importance of lower-tropospheric ozone to observed variations in atmospheric total column ozone and thus are important to the interpretation of total column measurements, especially for tropospheric studies. ¿ American Geophysical Union 1996