All data used was downloaded from the United States Environmental Protection Agency. I downloaded the annual air quality index by county files from 1980-2018. I also downloaded the site listing files. The files on the website are of type .csv that were then uploaded into my R project (Using RStudio). Lastly, I then merged all air quality index files into one table in order to access all county data from 1980-2018 in my R project.
Link to data:
annual_aqi_by_county_2018 - annual_aqi_by_county_1980