Monthly mean concentrations of ozone

SUMMARY:
       The ozone data set has 552 rows and  3  columns.  The
       first  column is the mean monthly ozone (O3) concentration
       in Dobson units of the ozone layer at Arosa,  Switzerland,
       from 1926 to 1971.

DATA DESCRIPTION:
       This data set contains the following columns:
ozone:    mean monthly ozone in Dobson units
year:     year
month:    month

SOURCE:
       Andrews and Herzberg, 1985, p. 75-76.