A NASA aircraft studying air quality and pollution flew at a low altitude Tuesday morning and afternoon across parts of Chicago and Northwest Indiana.

The aircraft, a four-engine DC-8 jet, took off from Dayton, Ohio, about 9:50 a.m. and passed through Chicago, surrounding suburbs and parts of Northwest Indiana, according to FlightAware, the aircraft tracking app.

The aircraft was scheduled to arrive back in Dayton around 6:15 p.m., according to FlightAware.

The approximately eight-hour flight is part of NASA’s “AEROMMA project.” From the end of June to the middle of August, the aircraft flies low over several cities to collect data on human-based pollution sources, according to NASA.

Other cities included in the project include Los Angeles, New York and Toronto. The DC-8, “the largest flying science laboratory in the world,” flies low over the cities to investigate urban emissions and the atmospheric chemical reactions that affect air quality and climate, according to a news release from NASA.

Those looking to follow the plane can do so on FlightAware, using the tail number N817NA.