What kind of fumes would come from mowing the lawn? Unless you have a professional yardman that sprays insecticdes or other "pest deterrents?" Just to be on the safe side, I would close all the windows, and run the air for awhile.... and maybe find out where the smell was coming from. The guy that does our lawn always tells us if he's going to use something that won't be safe for our animals, and usually does the front and back on seperate days, so we won't have too big a problem.