Earlier this year we learned that Google was using Street View cars to do more than just take pictures — some of them were also mapping air quality. Today the company announced that the program will expand to the Los Angeles, San Francisco, and Central Valley regions of California. The company says it's focusing on cities in California because of their high concentrations of particulate pollution, which contributes to more than a billion dollars per year in health care costs.

A trial run of the program was performed earlier this year in Denver, Colorado. Three cars were equipped with sensors from a company called Aclima, which enable them to study pollutants like carbon dioxide, methane, black carbon, and particulate matter on a per-block basis. They collected data for 750 hours over the course of a month, and some of the data from this trial was published by Aclima.

Going forward, Google said today that this data will eventually be overlaid on Google Earth and Google Maps, and it will also made available to scientists and air quality experts — specifically the Environmental Protection Agency and the Environmental Defense Fund.

Google and Aclima say that those three Street View cars are now roaming San Francisco, and the program will reach the other areas in 2016. Beyond that, there's no additional detail on how much of the Street View fleet will be devoted to the program.