To identify the most and least environmentally friendly states, 24/7 Wall St. created an index based on the following measures: prevalence of “green” transportation in commuting to work, average daily PM 2.5 (presence of fine particulate matter less than or equal to 2.5 microns across), the percentage of counties within a state with an average daily PM 2.5 greater than 12, consumption of renewable energy, and the population living in non attainment zones for sulfur dioxide, lead, PM 2.5, and 8-hour ozone.
Green transportation is classified as carpooling, using public transportation, walking, biking, and those who work from home, and this data comes from the U.S Census Bureau’s American Community Survey for 2016. Average daily PM 2.5 and the percent of counties with an average PM 2.5 greater than 12 comes from the County Health Rankings. Renewable energy consumption as a percentage of total energy consumption comes from the Energy Information Administration (EIA) and is for 2015, the most recent year available.
Data on non attainment areas (an area that is not meeting the standards for air quality set forth by the Clean Air Act) comes from the Environmental Protection Agency (EPA)’s Greenbook, and is current as of March 31, 2018. It is worth noting that an area that is classified as “non-attainment” is required by the Clean Air Act to immediately take steps to improve the quality of the air. As such, updates to the attainment status of an area may have changed in the time since the Greenbook was last updated, or an area may be in the process of working with the EPA to have their attainment status formally changed, which takes around a year to complete. Population estimates for non attainment areas are from the 2010 census.