Wood pellets generally burn smoke free at a superheated temperature. A few are added at a time to a small fire, with forced air combustion.
The combustion gases must pass through the red hot coal bed for full oxidation, and then through a good heat exchanger.
But I'm sure not all pellet stoves are created equal.
Conclusion: Wood stoves are convenient to blame for what is actually another source of the smog
That’s why we must persuade the Brits to use American LNG for home heating and cooking.