A new study finds nearly 18,000 premature deaths in the U.S. are caused each year by pollution generated by farms. Animal farming is the leading culprit. Particulate matter created by gases from manure and animal feed, which can mix with other pollutants in the atmosphere, is highly irritating to human lungs and accounts for more deaths than pollution from coal power plants. Scientists say more sustainable farming practices and reducing our consumption of meat would sharply reduce mortality from agricultural air pollution.