Ammonia is only one of the gases released from farms that has an unpleasant odor.
Many other gases also irritate the human nose. Some of these are not only unpleasant but also dangerous. High concentrations of this gas can be released when liquid pig manure in tanks is stirred. It can be fatal to humans, though only at high concentrations produced where ventilation is poor. To date, people have perceived farm odors only as nuisances, but awareness of this problem is now growing.