Oh, and you want to get me started on cars now?
Do you remember what happened when cars didn't have catalytic converters? all that shit that was emitted by exhaust went up into air, and fell back down to earth shortly thereafter. Since the introduction of the catalytic converter, the particles in exhaust get broken down again, so that they're extraordinarily tiny, and stay in the atmosphere when they go up.
Thank you, Mr. catalytic converter. I certainly do like hydrocarbons in my air.