This data set contains yearly observations by the Environmental Protection Agency on the concentration of sulfur dioxide in parts per billion, based on 32 sites. I use this for in-class illustration. Note that the national standard is 75 parts per billion. Data are the national trend.

so2concentrations

## Format

A data frame with the following 4 variables.

year

the year

value

the mean concentration of sulfur dioxide in the air based on 32 trend sites, in parts per billion

ub

the lower bound of the value (10th percentile)

lb

the upper bound of the value (90th percentile)

## Source

Environmental Protection Agency, 2021. https://www.epa.gov/air-trends/sulfur-dioxide-trends