Snow does put nitrogen into the ground when it falls. In fact, it has enough nitrogen that it has a fertilizer reputation because it feeds nitrogen to the soil slowly over time at a rate it can be absorbed.
Nitrogen is also found in rain in higher amounts. But rain tends to saturate the ground more quickly and run off, whereas snow melts more slowly, absorbs more gradually and therefore provides a slow feed to the ground beneath.
The atmosphere is around 78% nitrogen gas (N2) which is a compound made of two bonded nitrogen atoms. The amount of nitrogen in precipitation has increased since the industrial revolution due to pollutants in the atmosphere. Lightning also produces nitric oxide which travels down to the earth during precipitation. Altogether, the nitrogen compounds are deposited on the ground at an estimated rate of 5-10 pounds per acre per year. But the N2 that comes down from the sky can’t be used by plants until it has been converted into mineralized nitrogen.
China has been experiencing higher levels of nitrogen-containing pollutants as a result of agricultural, transportation and industrial increases in the past 30 years. Once nitrogen pollutants, such as ammonia and nitrogen oxides made it to the air, they can be transformed to secondary pollutants like ammonium and nitrates. When washed down to earth by the rain and snow, these pollutants can cause great harm to the earth, including soil acidification and the fertilization of harmful algae.