Measuring Acid Rain

The acid in the atmosphere reaches the soil in two ways: wet deposition and dry deposition. While wet deposition occurs chiefly in the form of rain, fog and snow, dry deposition mainly consists of acidic gases and particles that settle on the earth's surface.

This acidic deposition has an adverse effect on the plants, animals and aquatic life, and also affects the ecosystem. While certain species of living organisms are more resistant to this acidity, others are not.

This disturbs the food chain that is an integral part of any ecosystem. The extent of damage, however, depends on the degree of acidity and the chemical composition of the soil. The acidity of any substance is measured by the pH scale. Lower the pH value, the more acidic the substance is.

The pH value of distilled water (water that is free from all impurities) is 7 and this value is considered as neutral pH.

The primary cause responsible for acid rain, is the presence of acidic gases in the atmosphere, which gets dissolved in the rainwater. When water vapor precipitates to form droplets of water, in the higher layers of the atmosphere, the pH value is close to 7, i.e. neutral.

When atmospheric carbon dioxide (CO₂) gets dissolved in it, its pH value reduces to 5.5. However, as this rainwater passes through the different layers of the atmosphere to reach the earth's surface, acidic gases get dissolved in the rainwater, further reducing its pH value to something around 4.3.

If we analyze then, we find that the gases greatly responsible for causing acid rain are sulfur dioxide (SO₂) and oxides of nitrogen such as nitric oxide (NO). Produced as a result of burning of fossil fuels such as coal and petroleum, these gases react with atmospheric oxygen and moisture to produce sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

The list of damages caused by acid rain is seemingly endless. Water bodies and marine ecosystems are worst hit by acid rain, as all the acid ultimately reaches the lakes, rivers and smaller water bodies.

This results in major change in the pH levels of the water, which is a potential threat to the rich aquatic life, both flora as well as fauna. Also, the low pH results in the soil releasing aluminum and magnesium, which are toxic for plant life.

Acid rain curbs the growth of trees and causes irreversible damage to parts, such as the roots, stem and leaves. Weak roots leave the plants incapable of withstanding rough weather and, in time, they die. Prolonged exposure to acid rain, can even cause erosion of buildings, sculptures, pillars and other architectural structures.

Determining the degree of acidity in acid rain, is essential to keep a tab on the acid content in the atmosphere. The good news is that it is a simple process and can be practically carried out by anyone, with just a handful of equipment. For measuring the pH of acid rain, all you need are the following.

• Data logger
• pH sensor
• pH electrode
• sensor cable
• 50 ml beakers
• Marker pen
• Acid rain sample
• Tap water sample

Once you are ready with the things enlisted above, just follow these simple steps given below to measure acid rain.
Switch on the data logger and connect the pH sensor and the pH electrode together.

1. Now remove the pH electrode from the buffer storage and rinse the bulb with water.
2. Now use the sensor cable to connect the pH sensor to the data logger.

3. Dip the tip or bulb of the pH electrode into the sample of acid rain and once the reading stabilizes, note its pH value in the data logger.

4. After that, dip the tip of the pH electrode into the sample of tap water and note the pH value as shown on the data logger.

This is to compare the pH values of both the samples.
So, having noted the pH values of both, tap water as well as acid rain, you will find that the pH value of acid rain is lower, when compared to tap water. If you use distilled water for the same experiment, you'll find that the difference in pH is even greater.

This was briefly about measuring acid rain, its characteristics and effects on living beings. We can protect the earth from the ill-effects of acid rain by following the principle of conservation of energy and choosing alternative sources of energy such as geothermal energy, solar energy or wind energy.