Much to the chagrin of California tourism promoters, smog is likely one of the things you picture when you think about the city of Los Angeles. The haze of pollutants that often hangs over the city is more than just an eyesore; it’s a source of considerable respiratory stress. And where does that air pollution come from? Smokestacks, tailpipes, and cows. You read that right—cows. In fact, a new study estimates that cows contribute at least as much as automobiles.