Twenty-three years ago, Beijing's air was so thick with pollution that the city was nicknamed "Greyjing." Fine particles reduced visibility to metres, residents wore masks long before it became a global habit, and the smog was routinely visible from space.
Today, Beijing has cut its PM2.5 levels by more than 45% since 2010. In 2025, its annual PM2.5 concentration fell below 30 micrograms per cubic meter for the first time in recorded history. Heavily polluted days dropped from 58 in 2013 to just one in 2025.
Beijing is one of 19 major cities highlighted in a report released this month by the Breathe Cities initiative, titled "Breathe Better: How leading cities have rapidly cut air pollution." Published on March 11, 2026, the report found that these cities — including London, San Francisco, Hong Kong, Paris, and Seoul — had collectively reduced levels of two key pollutants by more than 20% between 2010 and 2024.
The two pollutants are PM2.5 (fine particulate matter) and NO2 (nitrogen dioxide). Both are linked to heart disease, lung cancer, stroke, and respiratory conditions. Together, they kill an estimated 7 million people globally per year.
What Actually Changed
The improvements didn't happen by accident. The report attributes them directly to deliberate policy interventions — and the cities that improved most were the ones that committed to multiple measures simultaneously.
London introduced the Ultra Low Emission Zone (ULEZ) and expanded it multiple times, added cycling infrastructure, and electrified its bus fleet. NO2 levels fell by over 30% since 2010, with 99% of monitoring sites showing improvement. PM2.5 dropped by almost 30%.
Beijing implemented large-scale "coal-to-clean" transitions — replacing coal-burning boilers with gas and electric heating across millions of households — while introducing vehicle restrictions, higher fuel standards, and a dramatic expansion of electric vehicle infrastructure. The turnaround is now being studied as a model for other rapidly industrialising cities.
San Francisco — the only North American city on the list — reduced both PM2.5 and NO2 by nearly 25% through a combination of electrification commitments, reduced car dependence, parking reform, and a city-wide air quality risk assessment that targeted the highest-burden communities first.
Why This Matters Beyond the Numbers
Clean air has historically been framed as an environmental issue. Increasingly, it is being understood as a public health and social justice issue — because air pollution disproportionately affects low-income communities, people of colour, and those living near industrial zones or major roads.
The cities in the Breathe Cities report also tended to share something else: political will. Every improvement was the result of contested decisions — charging zones that faced legal challenges, cycling lanes that prompted backlash, coal plant closures that required retraining workers. The air got cleaner because leaders chose to make it a priority and stuck with those choices over years and decades.
The World Health Organization estimates that 99% of the world's population breathes air exceeding WHO guideline limits. Even the cities in this report haven't reached those guidelines yet. But they have demonstrated that change is possible, that the tools exist, and that the benefits — to health, to productivity, to quality of life — are real and measurable.
Nineteen cities proved it in fifteen years. The question now is who is next.
Sources: Breathe Cities — "Breathe Better" report (March 11, 2026) · The Guardian (March 12, 2026) · Good News Network · Human Progress · SF Environment · Transport for London
