The facades of some buildings are already irreversibly damaged to a depth of 1 cm below the surface and will crumble in the near future.
The geography of Bath, in a 'bowl' surrounded by hills, traps airborne pollution and allows the concentration of traffic fumes to rise to levels which are dangerous to health. This bowl shape also makes a Ring-Road almost impossible to construct , so there is no way of diverting the through-traffic from the city centre except through other local routes.
Replacing petrol-engined vehicles with diesel-engined
ones will change the mix of pollution but will not remove it.
Diesel engine exhaust is a major source of spongy carbon particles
(PM10s) which adsorb quantities of dangerous chemicals on their
surface. PM10s are so small that they evade the body's defences
and are deposited in the lungs where the chemicals are deposited
to the detriment of health.
Diesel exhaust particles also blacken buildings and the unburnt fuel particles form a film which promotes algal growth.
More about Pollution in a Heritage City?
More about Bath's Traffic Problems?