One of the debates currently raging between environmentalists and the agricultural industry concerns factory farms. These are large, usually corporate-owned facilities in which there are high concentrations of livestock or where vast areas of cropland contribute to fertilizer runoff. When it comes to air pollution, such farms are a major contributor to the problem. So much animal waste is generated by factory farms, that large lagoons filled with manure and urine have to be built to maintain all of it. Some of this liquid manure is dispersed by spraying it onto crops as fertilizer, but that doesn’t really help the issue. These wastes generate large amounts of noxious pollutants, including ammonia gas, methane, and hydrogen sulfide, as well as carbon dioxide. Such gases contribute to acid rain and ozone depletion. In addition, livestock flatulence (to put it bluntly, burping and farting cows) is another source of methane gas. According to the Environmental Protection Agency, 20 percent of methane gas generated by human civilization comes from agricultural activities.