It's called PM 2.5, and it's a particularly nasty type of particulate matter found in the air around roadways. It can cause health problems, and as you can imagine it is especially heavy during rush hour traffic. But in a new study from researchers including Rodney Weber, a professor in the School of Earth and Atmospheric Sciences, PM 2.5 was also found inside cars at twice the levels previously estimated. The data was collected by devices placed on car passenger seats during Atlanta's morning commute.