Acid Rain Acid rain is caused by extra amounts of sulphur dioxide and nitrogen oxides. Natural sources of sulphur oxides and nitrogen oxides do exist, but are balanced by nature. Normal rain reacts with alkaline chemicals from the region's bedrock that are in the air, soils, lakes, and streams. This neutralizes the rain. However, if rain is more highly acidic, then the natural neutralizing chemicals can eventually become depleted. This is what is happening with more than 90% of the sulphur and 95% of the nitrogen emissions coming from humans. Approximately 40% of the nitrogen oxides come from transportation, about 25% from thermoelectric generatin