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Rain is very important for life. All living things need water to live, even people.
Rain brings us the water we need. But in many places in the world even where you live, rain has become a menace.
Because of pollution in the air, acid gases from factories, cars and homes, the rain is becoming dangerous for the life of every living creature.
This rain is known as 'acid rain'.

WHAT IS ACID RAIN?
Acid gases are produced when fossil fuels like coal and oil are burned in power stations, factories and in our own homes. Most of these acid gases are blown into the sky, and when they mix with the clouds it can cause rain - or snow, sleet, fog, mist or hail - to become more acidic.
The opposites of acid are alkalis; for example, toothpaste and baking powder are both alkalis. Strong alkalis can also be dangerous, such as ammonia and bleach.
Lemon juice, vinegar and cola are all acidic. Rain is naturally acidic, but acid gases make it even more acidic, sometimes as acid as lemon!
Nature can also produce acid gases, such as volcanoes. When they erupt, the smoke that comes out of the crater is also full of acid gases.

HOW DO WE MEASURE ACIDITY?
There is a special scale called the pH scale that measures the strength of acids and alkalis. A low pH number means something is acid. A high number means something is alkali. And something in the middle is called neutral.
Acidity can be tested using litmus paper.
Usually rain is a little acidic, and has pH of about 5.5, if the pH of rainfall is less than 5.5, then the rain is probably polluted by acid gases.
Acids turn litmus paper red, and alkalis turn it blue. With a special paper called universal indicator, you can test levels of acidity.

WHAT ARE THE MAIN GASES THAT CAUSE ACID RAIN?
When we burn fuels, chemicals called 'sulphur' and 'nitrogen' are released into the air. Once in the air, they...