Chicago ranks among the top 10 metro areas when it comes to clean technology.

Chicago moved into 10th place from 12th, while the state of Illinois continued to be ranked eighth in the U.S. Clean Tech Leadership Index, an annual ranking compiled by Clean Edge, a research firm based in Portland, Ore.

The city's ranking improved because of improvement in investment, innovation and workforce. The report credited Mayor Rahm Emanuel's creation of the Chicago Infrastructure Trust, a public-private partnership that has focused on energy efficiency and solar projects, though deals have been slow to materialize. Chicago also gets high marks for energy disclosure requirements for buildings and other "green-building standards."

Chicago is not in the top 10 in venture investment in clean tech or patent output.

California, Massachusetts and Oregon were the top-ranked states; the leading cities were San Francisco, San Jose, Calif., and Portland.

Illinois is the only Midwestern state in the top 10, helped by assets such as Argonne National Laboratory near Lemont; Energy Foundry, a Chicago-based accelerator for clean-tech startups; and a green master's degree program.

The state ranked fourth in total venture-capital investment in clean tech at $198 million, but ninth in per capita investment, trailing Missouri. Illinois ranked seventh in clean-energy patent output.

The state also benefits from regulations and incentives passed, such as energy efficiency rebates and renewable-energy targets, though implementation of regulations sometimes has been limited.

The index looks at a range of factors, such as renewable-energy targets and electric vehicle use. (Illinois is lacking in the electric vehicle department.) For states, criteria include technology, regulation, and financial and intellectual capital. Metro areas are judged based on green buildings; advanced transportation; clean-tech investment, innovation and workforce; and clean electricity and carbon management.