Air pollution is a well-known villain in the modern world. The dark smoke emanates from cars and factories, while big cities have been blamed for everything from climate change to the reduced visibility of the stars in the night sky.

But the scourge of urban smog isn't the only thing that contributes to air pollution. In fact, it might be time to point the finger of blame at a surprising culprit: farms.

Agricultural land in California alone contributes to between 25 and 41 percent of the nitrogen oxide in the air, a dismaying new study conducted by the University of California at Davis found. Nitrogen oxide is a blanket term for several compounds made of nitrogen and oxygen that contribute heavily to air pollution. While harmless in small quantities, large amounts of these gases can cause smog and even, in extreme circumstances, acid rain.

Writing in the journal Science Advances, researchers explained how large amounts of excess fertilizer, combined with the typical climate conditions of California, make for a stunning amount of pollution. While half of the nitrogen in fertilizer is used by the plants as nourishment, the other half sinks into the soil, where tiny bacteria convert the gas into nitrogen oxide. "Since you can't see it coming from the soils, it's very easy to miss," Ben Houlton, one of the scientists who led the study, told Newsweek.

Unfortunately, this problem doesn't have an easy solution: Farming remains a major industry in California, which grows about half of the fruits and nuts produced in the U.S. Read more about the study at Newsweek. Shivani Ishwar