For the past year-and-a-half, Google has been secretly testing a new way to measure the air quality in city streets. They worked together with a startup company called Aclima, to attach special sensors to its street view cars. With this sensor, they measured different chemicals that are unhealthy to breathe in, like nitrogen dioxide, nitric oxide, ozone, carbon monoxide, carbon dioxide, methane, black carbon. Their technology is good enough now to bring air quality data into the world. The goal is to make these data available to citizens so local governments can see and act on pollution on their own streets. For example, if a city knows that certain roadways are full of smog, they could try and change the traffic situation.