Sutro Tower in San Francisco hosts the first of California?s regional greenhouse-gas detectors. Credit: S. Ragan/AP

California has begun installing regional greenhouse-gas detection systems in metropolitan areas, becoming the first US state to gather such regional data.

Sensors have been placed on Sutro Tower in San Francisco and Richland Tower in the Sacramento suburbs as part of the California Greenhouse Gas Emissions Project, a collaboration between state and federal agencies and universities. They measure greenhouse-gas concentrations twice a day.

The project ? started by researchers at the Lawrence Berkeley National Laboratory in Berkeley, California ? plans eventually to monitor gases at ten locations, using the data to help establish whether California is reaching its goal of reducing atmospheric greenhouse gases by cutting state emissions. At present these total about 550 million tonnes a year.