There is this report that says the risk of aerosol spreading on a commercial liner is low due to HEPA filters.
But it is not considering the cases when A/C is OFF. This seems to be quite common when the plane is on the tarmac but away from the gates. At the gate the air is supplied by the airport. There are numerous reports of planes being delayed for hours in hot weather and passengers suffering. I have been in that situation myself a few times.
This is explained on quora:
It's kind of a double-edged sword. Simply put, cabin air in flight comes from intakes just behind the engine compressors. In flight, you're getting fresh, clean air that is inducted, mixed and filtered. It circulates through the cabin and eventually, lots of the circulated air gets sucked out by air blowing past the plane at nearly the speed of sound. However, its a different story when you're sitting on the tarmac. Engines at idle are still producing fumes, and these can get inducted along with fresh air because there's no air thrusting the fumes away from the plane as there is when you're moving at 500 knots. That mix can be filtered to a degree and is safe to breathe, but it's still going to smell awful, and even burn your throat. If you fly often, you'll often notice an awful smell of fuel when you get on the plane that clears up after takeoff. Granted, some of that smell at idle also comes from open passenger doors, but you get the idea. Also, due to changes resulting from in-flight fires, and 9/11, the pilots are isolated, and can often be unaware of how uncomfortable it is getting in the passenger cabin. Someone has got to bring it to their attention. Its not like a thermostat in your house, where you just set it and forget it. The crew has to control the cabin air on a more or less manual basis. Ever been to a restaurant that's freezing cold? Lots of times, the thermostat is controlled by people working in the hot kitchen, and the kitchen crew may not be aware (or even care) that their comfort is turning your fingers into icicles. Same principle.
So if the AC is OFF on the tarmac due to fumes, would it not make sense to use 100% recirculation in this instance and switch to fresh air whilst airborne? Can the pilot control this from the cockpit?