Explanation:

Globally, about 40 percent of total N2O emissions come from human activities. Nitrous oxide is emitted from agriculture, transportation, and industry activities, described below.
Agriculture: Nitrous oxide is emitted when people add nitrogen to the soil through the use of synthetic fertilizers.
Agricultural soil management is the largest source of N2O emissions in the United States, accounting for about 75 percent of total U.S. N2O emissions in 2015.
Nitrous oxide is also emitted during the breakdown of nitrogen in livestock manure and urine, which contributed to 5 percent of N2O emissions in 2015.
Fuel Combustion: Nitrous oxide is emitted when fuels are burned. The amount of N2O emitted from burning fuels depends on the type of fuel and combustion technology, maintenance, and operating practices.
Industry: Nitrous oxide is generated as a by-product during the production of nitric acid, which is used to make synthetic commercial fertilizer, and in the production of adipic acid, which is used to make fibers, like nylon, and other synthetic products.