acid rain
Rain in which the drops contain dissolved acids, as a consequence of the chemical combination of water with polluting gases present in the air. Acid rain is, therefore, a consequence of atmospheric pollution. It can be due to both natural causes (volcanic eruptions) and anthropogenic ones (atmospheric emissions). Both nitrogen oxides (NOx), as different sulfur-containing gases, coming from the combustion of coal and other fossil fuels, on reacting with the water vapor present in the atmosphere, give rise to various acids such as nitric acid (HNO3), sulfuric acid (H2 SO4), or sulfurous acid (H2 SO3), which end up incorporated into cloud droplets and from there into the various hydrometeors that form within them. When acid rain (or snow) falls on the Earth's surface, these chemical substances are deposited on it, causing harmful effects on vegetation and an acidification of soil and water.