What makes a city green? The latest COMMERCIALCafe study set out to identify the top 50 U.S. green cities currently making the most progress toward sustainability. COMMERCIALCafé looked at data on energy-related CO2 emissions reduction, improvements in air quality, differences over time in the share of walking and biking commuters, widening adoption of LEED-certified building practices, growth in environmentally-focused occupations, as well as detailed ratings by the ACEEE.

Here are some key findings:

Phoenix took #19 on the list, with a total of 51.99 points, surpassing cities like San Diego, Dallas and Las Vegas. Its strongest suits were median air quality improvement and city efforts geared toward sustainability.

• The city also added 131 LEED-certified buildings since 2014, bringing its total to 398.

• Overall, Washington, D.C., took the first spot on the list, with 72.68 points, followed by NYC and Denver.