How acid rain is formed? Explained with Reactions

How acid rain is formed? explained with reactions post explains about acid in the rain water’s, formation of acid rain, and acid rain reactions.

What is Acid Rain?

Acid in the Rain Water’s

Formation of Acid Rain

Reactions of Acid Rain

What is Acid Rain?

Although the phenomenon of “acid rain” (more correctly acid deposition) was identified in Manchester, England, as long ago as 1852, and described more thoroughly in 1872, modern scientific research has been going on only since the mid-1950s. Public concern about the problem began in the late 1960s. Acid rain is an environmental hazard that is transponder in nature. Northeastern America, North Western Europe and India are facing an acute problem of acid rain. Acid rain has affected certain rivers, lakes, streams and forests in United Kingdom (UK), United States of America (USA), Germany and many other countries.

Acid rain literally means ‘the presence of excessive acids in rain waters’. Acid precipitation is a mixture of strong mineral acids sulphuric acid (H2SO4), nitric acid (HNO3) and in some locations, hydrochloric acid (HCl). It usually has a ph of less than 5.6, the value of distilled water in equilibrium with atmospheric carbon dioxide.

Acid in the Rain Water’s

Acid rain problem is a result of anthropogenic activities. Most acids come from cars, homes, industries and power stations but some share is contributed by natural sources such as volcanoes, swamps and planktons. The acid problem is basically associated with the transport and subsequent deposition of oxides of sulphur, nitrogen and their oxidative products. These are produced by combustion of fossil fuels, power plants, automobile exhausts and domestic fires etc.

Formation of Acid Rain

Acid rain is one of the form of acid deposition which can either be wet or dry, acid rain, snow, dew, fog, frost and mist are the wet form of deposition, while dust particles containing sulphate and nitrates which settle on ground is called dry deposition.

Coal, fuel wood or petroleum products have sulphur and nitrogen. These elements, when burnt in atmospheric oxygen,’ are converted into their respective oxides (SO2 and NO3), which are highly soluble in water. By anthropogenic and by natural sources, oxides of sulphur and nitrogen enter the atmosphere.

Reactions of Acid Rain

How acid rain is formed explained with reactions

Figure 1: This image illustrates the pathway for acid rain in our environment: (1) Emissions of SO2 and NOx are released into the air, where (2) the pollutants are transformed into acid particles that may be transported long distances. (3) These acid particles then fall to the earth as wet and dry deposition (dust, rain, snow, etc.) and (4) may cause harmful effects on soil, forests, streams, and lakes. Image Source:

Reaction with Sulphur

S + O2 = SO2

2SO2 + O2 = 2SO3

Reaction with Nitrogen

NO + O3 = NO2 + O2

NO3 + NO2 = N2O5

When air is saturated with water droplets (humid conditions), N2O5 invariably reacts with water vapors to form droplets of HNO3.

N2O5 + H2O = 2HNO3

Besides some HNO2 is also formed

N2O3 + H2O = 2HNO2

SO3 in humid conditions forms droplets of H2SO4.

SO2 + 1/202O2 + H2O=H2SO4

HNO3 and H2SO4 thus formed combine with HCl to generate precipitation, which is commonly referred to as acid rain.

The primary reason for concern is that acid deposition acidifies streams, and taken on coarse, sandy soils low in lime: The effect is seen particularly in headwater areas and in wet montane environments, wherever sulphate loading from anthropogenic sources is strong. The chemical and physical consequences of lake acidification include, increased leaching of calcium from terrestrial soils, mobilization of heavy metals such as aluminium, zinc, and manganese and an increase in the transparency of lake waters. The biological consequences include market changes in communities of aquatic plants and animals, with a progressive lessening of their diversity.

Acid deposition may further impoverish forests soils, developed on sandy substrata poor in lime. As a consequence of accelerated leaching of nutrients, such as phosphorous, potassium, magnesium and calcium from these soils, forest productivity would eventually be reduced. Moreover, the acid sulphate particles that contribute to acid precipitation are in the size range that penetrates deep into the lung, and they may well exacerbate lung diseases and increase mortality rates.

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