This data set contains yearly observations by the Environmental Protection Agency on the concentration of sulfur dioxide in parts per billion, based on 35 sites. I use this for in-class illustration. Note that the national standard is 75 parts per billion.
A data frame with 40 observations on the following 4 variables.
the mean concentration of sulfur dioxide in the air based on 35 trend sites, in parts per billion
the lower bound of the value (10th percentile)
the upper bound of the value (90th percentile)
Environmental Protection Agency, 2020. https://www.epa.gov/air-trends/sulfur-dioxide-trends