Where is the primary site of ammonia gas accumulation within deep-litter brown layer sheds, and where should exhaust fans be placed?

Ammonia gas ($NH_3$) is highly soluble in water and is generated by the bacterial decomposition of uric acid in poultry manure. Because ammonia gas is lighter than air when dry, but rapidly binds to humidity in a warm, moist poultry shed, it forms a heavy, toxic micro-climate. This gas accumulates primarily at the floor level—the exact micro-zone where the birds reside, breathe, and sleep (between 0 and 12 inches above the litter). High ammonia levels (above 20 ppm) paralyze the tracheal cilia of the chickens, opening the gateway for E. coli and respiratory pathogens. To evacuate this heavy, humid gas, exhaust fans must not be placed high on ceilings; instead, minimum ventilation exhaust fans must be placed low on the end walls (no higher than 2 to 3 feet from the floor level) to draw air directly across the litter surface and pull the ammonia pocket out of the building. Farmers can study gaseous thermodynamics in the Poultry Encyclopedia, buy ammonia gas detectors and exhaust fans on Poultry Plaza, track daily market rates on Poultry Rates, and list respiratory-disease-free flocks on Murghi Mandi.