From Cleveland (1993): The data are daily maximum ozone concentrations at ground level on 132 days from May 1,1974 to September 30,1974 at two sites in the U.S.A. — Yonkers, New York and Stamford, Connecticut — which are approximately 30 km from one another. The sample for each measurement is the air mass on a particular day, and the bivariate data arise from two measurements at the two sites.
ozone
A data frame with 132 rows and 2 variables:
day
air mass at Yonkers
air mass at Stamford
Cleveland W. S. (1993). “Visualizing Data”. Hobart Press.