Foggy breath and car exhaust.

One thing I had noticed long ago is that if you breath in a little car exhaust (just by being near a running car) that you are more likely to be able to see your breath in cold weather.

I assume it's because the air is different enough to conduct the heat from inside your lungs faster than regular air.

The building Amazing and I work in is right next to a freeway.  The back of the building faces the freeway.  When we got back from lunch today, I parked in the back and when we got out of the car I noticed I could see my breath, but didn't notice that when we left the restaurant just down the street and only minutes before.

I told Amazing it was because of the exhaust of the freeway, and that our breath would be noticeably less foggy looking even just in front of the building where the building would separate us from the freeway.

Amazing wanted to try it out, and sure enough, we could hardly see our breath at all in front of the building; where the back of the building, next to the freeway, it was pretty hard to miss.

Can someone provide a better explanation of the phenomena than I have provided?  I'm sure there is much more science to it, and I wouldn't mind knowing.