Manure is source of many harmful gases

According the United States Department of Agriculture (USDA), the amount of manure generated in 2005 was estimated to be over 335 million tons of dry matter per year.  Much of this manure comes from concentrated animal feeding operations (CAFOs).  The largest 2% of all CAFOs produce over 40% of all animals, according to the USDA. Often, there isn't enough need for all the manure generated at these huge animal farms.  Instead of being used as fertilizer, the extra manure ends up being stored nearby the animal facilities where it decomposes and releases noxious pollutants.  The four main gases produced by this manure are hydrogen sulfide, methane, ammonia, and carbon dioxide.

> Hydrogen sulfide is an odorant and can be a harmful indoor air pollutant. It comes mostly from animal sources.
> Methane is an extremely efficient greenhouse gas.
> Ammonia can cause damage to crops and lead to soil acidification.
> Carbon dioxide is a greenhouse gas.

However, the majority of manure is still spread or sprayed over agricultural land as fertilizer.  This utilizes excess manure and is beneficial to the soil, but it also releases particulate matter, more volatile organic compounds, and pathogens, in addition to the other pollutants listed above.

Animals are a huge source of air pollutants, and measures must be taken to properly dispose of or utilize their waste products.

Sources:
1: http://www.ars.usda.gov/research/programs/programs.htm?np_code=206&docid...
2: http://www.sustainabletable.org/issues/airpollution