what source releases nitrogen oxides into the atmosphere?

Vehicles release nitrogen oxides into the atmosphere. In the internal combustion engines of vehicles, electric sparks provide sufficient energy for the reaction between nitrogen gas and oxygen gas in the air to produce nitrogen monoxide.
N₂(g) + O₂(g) → 2NO(g)
When nitrogen monoxide is released to atmosphere, it reacts with oxygen in the air to give nitrogen dioxide at room temperature.
2NO(g) + O₂(g) → 2NO₂(g)

Also, power plants also release nitrogen oxides into the atmosphere. The high temperature in burning of fuels provide sufficient energy for the reaction between nitrogen gas and oxygen gas in the air to produce nitrogen monoxide.

internal combustion engines