Where does air pollution come from?

What still baffles me is the reduction in SO2 emissions due to regulations on shipping fuel.

How did the shipping industry accept / manage / afford to switch fuels (presumably, to more expensive ones) in order to follow the regulation ; as opposed to delay / deny / deflect, or plain old lobbying the hell against the changes ?

Are we in a "Montreal protocol" situation, where the alternative was existing and acceptable and in the same price range ?

Or did one actor implement coercion differently ? Was a standard change made, that enabled drop-in replacement ?

(If we were living under Discworld-like physics where narrativium existed, I would understand _why_ the change happened : it's making climate change worst, so of course there is all the power of narrative irony.

Are we in a world governed by narrative irony ? That would explain so many things...)

Are we at the point where corporate adherence to laws is considered shocking?

To be honest: yes, at this point, and with an industry of this scale, it's a bit shocking to me.

I don't know the main actors here, but I imagine the leverage of shipping companies on western countries is incredible ? ("oh, you think our boats are too polluting ? sure, let's see how you bring "about everything that's sold in about all your shops but that is manufactured half a world away" without our boats.")

Yes

And especially considering its usual resistance to change

I speculate that it's the ports which make the rules and they're not bothered by having to charge more for fuel, as ships are wholly dependent on that. Meanwhile local authorities can put pressure on ports to not provide certain types of fuel.

When maritime shipping quintupled in price during the pandemic it wasn't because ship operators suddenly figured they could fleece people like that - it was the ports' logistics which were all out of whack.

I would bet the main forcing being insurance companies. There are only a handful of those and while they are powerful, they are also subject to (western) courts. And if (essentially) the US says: If you insure a ship using the wrong fuel you will cease existing, those ships won't be insured. And ships are too expensive to run without insurance (at least most of them). But.. pure speculation

Ports could be the other player, but how would you coordinate the ~all ports?

Yes, e.g. compare that to agriculture where emissions are still increasing exponentially. The political power the farmers have is amazing, apart from the fact that they managed to get exempt from emissions penalties in many countries, they also continue to be able to push increased meat and dairy consumption which does not only increase pollution but has many other serious environmental and health impacts.

SO2 was the main driver behind the forest dieback. I'd estimate that the global investments in forrest property (mostly by old money) dwarfs the total cost for the switch to sulfur free fuel.

It is remarkable how fast the wheels of progress turn when old money faces the prospect of their assets being washed away.

Different people, though.