The Right Chemistry: I'll level with you; asphalt is problematic

It’s summer and the smell of asphalt is in the air. Road crews are out filling potholes, repaving roads and, of course, breathing the fumes. Pretty foul smelling stuff. Surely can’t be great for the lungs. As it turns out, it isn’t. Polycyclic aromatic compounds, or PAHs, are the problem and there’s no asphalt without these. 
So, what is asphalt and where does it come from? The source is petroleum, that dark viscous liquid found deep within the Earth, the product of