Sure thing, here's a report from the Greater London Authority tracking the history of air quality in the city since the "Great Smog" event 1952, which caused an estimated 4000 deaths.

https://www.london.gov.uk/programmes-strategies/environment-...

The main takeaway is that yes, urban air quality (including fine particulate matter) has improved massively over time, but most of it had little to do with road traffic, as for decades it wasn't a significant contributor to the overall mix. The important change was the move away from burning solid fuels like coal for household heating and in power stations within cities, to using gas and electricity with larger, out-of-town power stations.

As other sources have declined, road traffic has indeed become the largest contribution to urban air pollution, but even here there has been progress. Fine particulate emissions have continued to decline as car manufacturers have adapted to more stringent regulation (cheating scandals notwithstanding). A bigger problem now is higher non-exhaust emissions caused by larger and heavier vehicles. This is something else that will need to be solved via regulation. Other policies like Low Traffic Neighbourhoods can also help to restrict the worst pollution to major roads and away from where most people live.

Urban air quality is never going to be as good as that in the countryside, but it's not true to believe that no progress has been made, and that it's simply been a switch in the type of pollution.