Acid rain pertains to any form of precipitation (rain, fog, mist, snow) exhibiting higher acidity than usual (with a pH level below 5.6, as a pH below 7 indicates acidity). The occurrence of acid rain is attributed to atmospheric pollution stemming from acidic gases, such as sulphur dioxide and nitrogen oxides, released during the combustion of fossil fuels. Additionally, it is acknowledged that acidic smog, fog, and mist migrate out of the atmosphere and adhere to dust particles, subsequently accumulating on vegetation as acid depositions. Consequently, when precipitation, like rain, transpires, the acid derived from these depositions permeates and gives rise to acid dews.
GASES THAT CAUSE ACID RAIN
Origin of Acidic Gases:
Sulphur Oxides (SOx):
Sources:
- Fossil Fuel Burning
- Power Plants
- Smelting of Metal Sulphide Ores
- Industrial Sources
- Industrial Production of Sulfuric Acid in Metallurgical, Chemical, and Fertilizer Industries
- Volcanoes
- Seas and Oceans
- Decomposition of Organic Matter
Nitrogen Oxides (NOx – NO, NO2, and N2O):
Sources:
- Fossil Fuel Burning
- Lightning
- Biomass Burning
- Forest Fires
- Oceans
- Power Plants
CHEMISTRY OF ACID RAIN – ACIDIFICATION
The formation of acid rain involves six basic steps:
- Emission of Oxides:
- The atmosphere receives oxides of sulphur and nitrogen from both natural sources and human-made activities.
- Dry Deposition:
- Some of these oxides fall directly to the ground as dry deposition, either near their source or at a considerable distance.
- Sunlight Activation:
- Sunlight plays a role in stimulating the formation of photo-oxidants, including ozone, in the atmosphere.
- Chemical Interaction:
- Photo-oxidants interact with the oxides of sulphur and nitrogen, as well as other gases like ammonia (NH3).
- Acid Formation:
- The chemical interaction leads to the production of sulphuric acid (H2SO4) and nitric acid (HNO3) through oxidation.
- Wet Deposition:
- Acid rain, containing ions of sulfate, nitrate, ammonium, and hydrogen, falls to the ground as wet deposition.
HARMFUL EFFECTS OF ACID RAINS
Effects on Humans:
- Acid precipitation, with its detrimental consequences, adversely affects both aquatic and terrestrial organisms.
- It also poses significant threats to buildings and monuments. The repercussions on human health include unpleasant odors, reduced visibility, and irritation of the skin, eyes, and respiratory tract.
- Direct health impacts encompass chronic bronchitis, pulmonary emphysema, and an increased risk of cancer.
Effects on Soil:
- Acid rain induces leaching of essential nutrients in the soil, leading to decreased fertility.
- The exchange between hydrogen ions and nutrient cations, such as potassium and magnesium, causes nutrient leaching.
- This process results in an increase in ammonia levels and a decrease in nitrate levels, affecting decomposition rates.
- Notably, the impact on soil in India is relatively less due to the alkaline nature of Indian soils, which exhibit good buffering ability.
Effects on Aquatic Life:
- Acid rain has detrimental effects on aquatic organisms, affecting their reproductive processes and life cycles.
- The eggs and sperm of fish, frogs, and other aquatic organisms are sensitive to pH changes.
- Acidic lake waters can lead to the unproductivity and death of microbes. Additionally, acid rain can release metals bound in soils into the aquatic environment.
Effects on Terrestrial Life:
- Acid rain damages the cuticle of plant leaves and reduces photosynthesis.
- The acidic medium promotes leaching of heavy metals like aluminum, lead, and mercury, affecting soil microorganisms.
- Indirect impacts on wildlife include the loss or alteration of food and habitat resources.
Effects on Microorganisms:
- The pH level plays a crucial role in determining the proliferation of microbial species. Most bacteria and protozoa prefer a near-neutral pH, while fungi thrive in an acidic environment.
- The shift in pH levels can alter the composition of microbial species in soil and water, causing a delay in the decomposition of organic material.
Effects on Buildings and Monuments:
- Historical buildings, monuments, and artworks are adversely affected by acid rain.
- Limestone and marble, commonly used in historical structures, are particularly susceptible to dissolution and flaking due to acid fumes in the air.
- This phenomenon, often referred to as “Marble Cancer,” has affected renowned structures like the Taj Mahal in Agra.
FAQs – ACID RAIN – ACIDIFICATION
Q1: What is acid rain, and how is it defined?
A1: Acid rain refers to any form of precipitation, including rain, fog, mist, and snow, that exhibits higher acidity than normal, characterized by a pH level below 5.6. A pH below 7 indicates acidity.
Q2: What causes the occurrence of acid rain?
A2: Acid rain is primarily caused by atmospheric pollution resulting from acidic gases, such as sulphur dioxide and nitrogen oxides. These gases are released during the combustion of fossil fuels.
Q3: Are there other forms of acidic atmospheric phenomena besides rain?
A3: Yes, besides rain, acidic smog, fog, and mist can form in the atmosphere. These acidic components migrate and settle on dust particles, accumulating on vegetation as acid depositions.
Q4: How does acid rain form, chemically?
A4: The formation of acid rain involves several steps. Oxides of sulphur and nitrogen are emitted into the atmosphere, some of which fall as dry deposition. Sunlight stimulates the formation of photo-oxidants, leading to the interaction with these oxides and the production of sulphuric acid (H2SO4) and nitric acid (HNO3). Acid rain, containing various ions, then falls as wet deposition.
Q5: What are the sources of Sulphur Oxides (SOx) and Nitrogen Oxides (NOx)?
A5: Sulphur Oxides (SOx): Fossil fuel burning, power plants, smelting of metal sulphide ores, industrial sources, industrial production of sulfuric acid, volcanoes, seas and oceans, decomposition of organic matter.
Q6: What are the harmful effects of acid rain on humans?
A6: Acid rain negatively impacts both aquatic and terrestrial organisms. For humans, it can result in bad smells, reduced visibility, and irritation of the skin, eyes, and respiratory tract. Chronic bronchitis, pulmonary emphysema, and an increased risk of cancer are direct health effects.
Q7: How does acid rain affect soil?
A7: Acid rain induces leaching of essential nutrients in the soil, making it infertile. The exchange between hydrogen ions and nutrient cations causes leaching, resulting in increased ammonia levels and decreased nitrate levels. However, the impact on soil in India is comparatively less due to the alkaline nature of Indian soils.
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