Air Around Us-Introduction

Carbon dioxide
        In a closed room, if there is some material that is burning, you may have felt suffocation. This is due to excess of carbon dioxide that may be accumulating in the room, as the burning continues. Carbon dioxide makes up a small component of the air around us. Plants and animals consume oxygen for respiration and produce carbon dioxide. Plant and animal matter also consumes oxygen on burning and produces mainly carbon dioxide and a few other gases. It is advisable not to burn dry leaves and discarded remains of the crop, which pollute our surroundings.
Dust and smoke
        The burning of fuel also produces smoke. Smoke contains a few gases and fine dust particles and is often harmful. That is why you see long chimneys in factories. This takes the harmful smoke and gases away from our noses, but, brings it closer to the birds flying up in the sky! Dust particles are always present in air.
Activity 
Find a sunny room in your school/ home. Close all the doors and windows with curtains pulled down to make the 

oom dark. Now, open the door or a window facing the sun, just a little, in such a way that it allows sunlight to enter the room only through a slit. Look carefully at the incoming beam of sunlight.
        Do you see some tiny shining particles moving in the beam of sunlight
What are these particles? 
        During winters you might have observed similar beam of sunlight filter through the trees in which dust particles appear to dance merrily around!This shows that air also contains dust particles. The presence of dust particles in air varies from time to time, and from place to place. 
        We inhale air when we breathe through our nostrils. Fine hair and mucus are present inside the nose to prevent dust particles from getting into the respiratory system. 
        Do you recall being scolded by your parents when you breathe through your mouth? If you do that, harmful dust particles may enter your body. 
        We may conclude, then, that air contains some gases, water vapour and dust particles. The gases in air are mainly nitrogen, oxygen, small amount of carbon dioxide, and many other gases. However, there may be some
Composition of air
    variations in the composition of air from place to place. We see that air contains mostly nitrogen and oxygen. In fact,these two gases together make up 99% of the air. The remaining 1% is constituted by carbon dioxide and a few other gases and water vapour.