Wondering why I had 2 small trucks pass by me during my run this morning, and they were loud and smelled bad. For about 10 seconds I could clearly see my breath while running. Does this happen with heavy exhaust or was I breathing something potentially harmful? It was slightly concerning.
Mostly just curious since I’ve been a runner for a long time and have never had this happen despite trucks and cars passing by me all the freaking time.
In: Chemistry
Being able to see your breath in the air is not just a factor of temperature, it is also a factor of your body temperature, ambient humidity, and importantly, local visibility conditions. In cool dry weather your breath can still create fog, but it might be harder to see. When the trucks went past you, it probably changed the local lighting conditions (they might have cast a shadow on your for a moment for instance). When they were gone, the conditions changed again, throwing the fog of your breath into sharp relief so it became briefly visible. It wasn’t that the trucks did something to the air itself to cause your breath to fog, they just did something to the light or to the visual background that made the fog visible.
This may have been caused by the soot emitted by the trucks providing nucleation sites for water to condense. Your breath added extra humidity to the air and the soot could have seeded small clouds as a result.
My guess is that while running normally, the small amount of fog created by your exhalation in that temperature did not come to your field of view as you were running through the air, but the way in which those passing trucks created all sorts of air movement allowed you to see it briefly.
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