How can you think about air in a way where you can feel the scale of the relationship of air to the Earth. Here’s one: Imagine you have an onion.
Peel off the brown outer layer. When you reach the ball within, you will see a fine film on the outside of the onion. Gently peel that film back. It’s so fine you can see right through it. That film is our atmosphere and the onion is the Earth.
Like water, there is no substitute for air. When you run out of air to breathe, when it lacks the requisite oxygen for your body to use to process sugar for energy and breaking down what you eat to stay alive, you die.
We think there is a never ending supply of air available to us as a species. We think the air is limitless and can absorb any amount of our pollution and a good breeze will clear the air after a day or two.
The air has limits. The air is mobile, but not always. Smog over cities can linger for weeks, making air quality quite toxic in the long term. Triggering asthma, allergies, and reactions to chemicals and particulates trapped in such conditions.