Question

If pollutants keep adding tons of this and that to
the atmosphere, does the air get more dense, or just bleed off into space? And how does the answer relate to the ideal gas law?

Answer 1

The total mass of the earth's atmosphere is about \( 5 \times 10^{15} \) metric tons, so the effect of these gases is small, but not zero.

The increase in \( CO_2 \) in the atmosphere leads to an increase of the greenhouse effect, etc.

Now, does this mean the atmosphere on average gets more dense depends on a few things. Let's first observe that the average pressure of the atmosphere hasn't changed; i.e., P is constant. Hence what must be happening with T going up and n also increasing slightly, is the volume of the atmosphere must be increasing as well, as
PV = nrT

Given that if there are more molecules of CO2 (or other molecules of higher molar mass) than O2 in a gas of P = 1 atm at constant temperature, then yes, the density also slightly increases.

Answer 2

CO2 is not a pollutant. What about nanoscale particles and particulate matter e.g.
incompletely combusted fossil fuel? The greenhouse part I understand, it's the other
stuff that confuses me. Thanks.

Answer 3

Yes, by the same principle, because those molecules have a greater molar mass than atmospheric gases in general, they do increase the density of the air. But again, the effect is very small.