I explained to him that the air is not just polluted, it isn't even air anymore. Studies indicate that the air of today has less than 50% of the oxygen content it had just 100 years ago. The oxygen, essential to our health and well-being, is dwindling. The cause can be attributed to any number of things, including the decimation of the rain forests, which had been responsible for producing a large portion of the earth's oxygen. Rain forests were the Earth's "lungs".
Whatever the reasons, our air is of very low quality, and not suited to our needs, and is getting worse each year. This would explain why lung problems, such as asthma, have grown from almost nothing in 1950 to a worldwide epidemic in the present.
Unfortunately, there is little we can do about this situation on any large scale, short of re-foresting the planet. However, all is not completely lost...
Grandma had the right idea - have lots of green plants in every room. Plants absorb carbon dioxide and expel oxygen.
On a more "global" scale, if every person in the U.S. were to plant just one tree somewhere, that would be 320 million more producers of oxygen that "eat" the carbon dioxide that environmentalists are so worried about.
I planted 600 trees this year, and will plant 600 each year for 4 more years because I burn 20 trees each year for fuel. So, I add a lot more than I take. I also have a large vegetable garden, and a host of flower gardens. By producing food, beautifying the premises and growing a future fuel supply, I am adding a lot of oxygen, and reducing the carbon dioxide. But it is a mere, insignificant amount compared to what is needed.
But it is a start. And it is my part in the solution. How about adding your own? You do not need to own land in order to plant a tree in the forest, or even to have a window box of flowers, or plants in your home. We can all do a little. And when you add up 320 million "little" things, you have a LOT!