From Beijing to London: Cities show what happen when they crack down on polluting vehicles

By Ho Tan December 8, 2025 | 02:56 pm PT

Once struggling with severe air pollution, Beijing, Seoul, Tokyo and London show how their crackdown on emissions, especially from older diesel trucks and buses, can improve the cities' air far faster than most people expect.

Across Asia and Europe, cities that raised fuel and emissions standards by even one or two levels saw fine dust and toxic gases fall sharply within just a few years. The biggest gains came from phasing out old diesel models or forcing them to install particle-filter systems.

In Tokyo, the turnaround began in the early 2000s. The city introduced strict rules requiring diesel vehicles, particularly commercial trucks and buses, to retrofit diesel particulate filters (DPF) or stop operating altogether. By 2003, non-compliant diesel vehicles were banned from entering the city unless they had been upgraded.

Studies from Japan's environment ministry show these measures cut fine-particle emissions from trucks and buses by more than 40% between 2001 and 2003, enough for Tokyo to shed the smog it was known for in the 1990s.

Beijing followed a similar but more aggressive path. From 2013 to 2017, the city upgraded new-vehicle standards to China V (Euro 5) and removed large numbers of older China II/III vehicles. International research shows Beijing’s average PM2.5 levels fell by around 35% during this period. CO and NOx dropped too, thanks to tighter control of diesel freight fleets and parallel cuts to industrial and coal emissions.

Beijing under the clear blue sky on July 30, 2021. Photo by AP

Seoul paired stricter national standards with local action. Starting in 2005, the city restricted old diesel vehicles, subsidized DPF retrofits and gradually lifted national rules to Euro 4 and Euro 5. As cleaner engines and improved fuel quality took hold, Seoul’s average PM10 levels fell by roughly 30% from the early 2000s to the mid-2010s.

London’s transformation came later but was rapid. The Ultra Low Emission Zone (ULEZ), launched in 2019, barred gasoline cars below Euro 4 and diesel vehicles below Euro 6 from central London. Transport for London says roadside NO2 levels in the core zone dropped dramatically, in some locations nearly by half, compared to a scenario without ULEZ. PM2.5 fell more slowly but steadily around major roads.

Vietnam is now preparing its own emissions roadmap. From 2026, older vehicles will be required to meet Euro 1–4 standards depending on their production year. Hanoi and Ho Chi Minh City will adopt even stricter rules starting in 2027, phasing in Euro 4 and Euro 5 requirements and banning vehicles that fail to meet minimum thresholds by 2029.

Vietnam’s standards remain lower than those of Tokyo, Seoul, or London. But international experience is clear: even moderate upgrades, if enforced strictly and paired with the removal of non-compliant vehicles, can deliver visible improvements to urban air in just a few years.