The principal sources of atmospheric NH4 include: (1) pig and cattle farms in large agricultural operations; (2) cereal fields; (3) land transport, highways; (4) burning of fossile fuels in power plants; (5) photochemical processes in the amtosphere; (6) oil platforms in the sea; (7) marine transport, shipping.
There may be more than one correct choice.
Ammonia is a highly reactive and soluble gas. Both anthropogenic and natural sources can contribute to ammonia is the atmosphere. But the major contributor is the agriculture; manure, slurries and fertilizer applications. Overall the agricultural sector can contribute about ~80-90% of the total atmospheric emissions.
Livestock operations such as pig and cattle operations can contribute more than 50% of the total emissions. Significant portions of nitrogen provided to beef and dairy cattle end up in urine and manure. Beef cattle will only utilize 10% of the N input and dairy cattle will utilize about 35% of the N input. The rest of the N will end up in urine and manure. N in urine is highly volatile and will be converted into NH3 in the presence of urease enzyme. Therefore most of the animal husbandry operations such as pigs, hogs, cattle and even chicken will contribute the majority of NH3 operations. [Ref 1]
Fertilizer application in cereal production such as corn, wheat and rice production is the second most significant source of atmospheric NH3, especially when cereal production requires a huge input of nitrogen fertilizers each year. Fertilizers especially urea can be converted into NH3 after application which will be released into the atmosphere.
Therefore the answers are 1 and 2 (animal husbandry and cereal production).
Ref 1: Atmospheric Ammonia: Sources and Fate, NOAA. http://www.esrl.noaa.gov/csd/AQRS/reports/ammonia.pdf