It was found a dairy cow creates around 9 kg of volatile organic compounds (VOC) every year - more than a car - as well as large amounts of the greenhouse gas methane, possibly adding up to 20 percent of global emissions.
VOCs combine in the atmosphere with nitrogen oxides, emitted by cars, to form smog.
Cows should be more closely monitored, claims the San Joaquin Valley United Air Pollution Control District, which is behind the study.
Professor Jamie Newbold, of the Institute of Rural Sciences in Aberystwyth, told National Geographic: "In more rural communities as much as 50 percent of the methane comes from livestock.
"Actually it's belching, not farting, that's the problem. A full-grown dairy cow can belch 400 to 500 litres of methane a day."
The gases are produced by microbes in the cows' stomachs that ferment grass and food into a digestible state.
Professor Newbold went on to explain that gas creation is not only limited to cows as humans also produce methane, although without the necessary microbes it is limited to only a few millilitres.
Just to get the whole picture :p