Air pollution is a major issue around the world: It contributes to around 7 million deaths a year, according to the World Health Organization (WHO). People living in the world's largest cities, from Delhi to Istanbul or Los Angeles, are among the most affected. But a DW analysis reveals some surprisingly encouraging news: In many megacities, the air is slowly getting better.

This analysis focused on one measure of air pollution: PM 2.5, fine particulate matter made of various kinds of solid particles and liquid droplets that are 2.5 micrometer or less in size, much smaller than the width of a human hair. This is often used as an indicator for pollution levels in general.

"The smaller these particles are, the deeper they can enter the body," said Sophie Gumy of the WHO's Department of Climate Change, Environment and Health. She told DW that PM 2.5 is so small it can enter the lungs and bloodstream, where it can cause respiratory issues, heart disease and lung cancer.

Particulate matter in cities is mainly caused by emissions from cars and other vehicles. Solid fuels like coal, wood or kerosene, which are used for energy, heat and cooking, also contribute, along with industrial emissions and waste burning.

To find out how pollution levels have developed in recent years, DW analyzed data collated by Swiss data provider and manufacturer of air quality products IQAir, covering PM 2.5 levels for cities with a population of more than 10 million. Of the 25 megacities with available data, almost all (21 cities) had improved their air pollution levels between 2017 and 2022.

Tackling air pollution: 1. Clean transport

To combat air pollution, cities are implementing various strategies. In many, transport plays a significant role. Effective measures prioritize cleaner and fewer cars, promote walking or cycling and expand public transportation. Bangkok, for example, is expanding its — still limited — Skytrain and Metro services, while Delhi aims to electrify 80% of its bus fleet.

Zoe Chafe, technical Lead for air quality at C40, a network aimed at helping its nearly 100 member cities become more environmentally friendly, told DW that many are experimenting with low-emission zones as well. These are areas where only some or no cars are permitted, and street design might be adjusted to make more room for pedestrians and cyclists instead.

"This is something that's resonating across all regions of the world right now, and it's really exciting," Chafe said.

Tackling air pollution: 2. Industrial sources

Industry is another crucial aspect to address. Delhi's action plan against air pollution, for instance, also focuses on reducing dust from construction sites and transitioning to cleaner fuels and more efficient techniques. The city is still among the most polluted on the planet, especially in the winter months. In 2023, smog again got so bad it forced schools to shut. Even so, Delhi has decreased pollution levels by 15 % between 2017 and 2022.

One major factor may have been the Badarpur coal power plant, which was taken offline in 2018. It is estimated to have been responsible for around 10 % of the particulate matter air pollution in Delhi alone.

Tackling air pollution: 3. Waste management

Wherever waste isn't collected and processed appropriately, people resort to open burning. That causes toxic smog and contributes to air pollution. That means regulation and infrastructure for waste management has to be part of any city's plan against air pollution.

Even where laws exist, progress can be slow. "There are solid waste management bylaws from 2016, they are still not implemented," Bhavreen Kandhari told DW. The founder of the mothers' activist group Warrior Moms has been advocating for cleaner air across India for more than 20 years, petitioning the government and courts.

Tackling air pollution: 4. Clean energy

When measures are implemented thoroughly, the impact can be significant. Cities throughout China, for instance, have reduced their pollution levels drastically in the last few years.

This is the result of what the Chinese government calls a "war on air pollution," a bundle of measures targeting all major causes. Among them: energy consumption for heating and electricity.

Beijing, for instance, has imposed strict emission limits for household boilers and offered subsidies to any household making the switch from coal-fired boilers to natural gas or electricity. One study concluded that renovating these boilers accounted for 20% of the reduction in Beijing's air pollution.

Beyond China, countries worldwide are investing in renewable energy, phasing out coal and exploring alternatives to wood and coal-fired stoves. Seoul, the capital of South Korea, already transitioned to gas heaters in the 1990s, and is now considering more eco-friendly alternatives like heat pumps.

Key challenges: Better data

When cities want to improve their air quality, the first step is often to improve data collection. In Pakistan, for instance, there are still very few official governmental monitoring stations, making it hard to judge whether air quality is improving.

But people like Abid Omar, who founded the Pakistan Air Quality Initiative in 2016, are working to change this. "Like-minded individuals, corporations, organizations have come together with low-cost monitors and are providing data publicly on the internet," he told DW. "And that data is what is driving awareness."

Key challenges: Funding

For cities to make any real change, C40's Zoe Chafe said, financial resources are crucial.

"Beijing was able to put a huge amount of investment into the air quality problem," she said. "And that is the key question for a lot of other cities right now: Do they have the money to invest to make such a step change in their air quality?" 

China has invested more than 20 billion yuan per year, or several billion dollars, into air pollution control over the past few years.

Key challenges: Collaboration

Air pollution can move across large distances, transcending political boundaries. This is the case, for instance, in India, where crop burning in rural northern states brings severe smog to Delhi and the surrounding area each year after the harvest season. Similar issues affect, for instance, the Nile Delta around Cairo in Egypt, or Indonesia, where smoke from agricultural burns reach even into neighboring Singapore and Malaysia.

So cities, regions and countries will have to work together to change, said Chafe. "What we have at the heart of the matter is the health of people. It doesn't matter where air pollution is coming from, it's extremely important that it's reduced," she said.

Most cities still far exceed WHO air pollution limits

There is a lot left to do: Air pollution levels in almost all cities in the world still exceed the WHO's limit of 5 microgram per cubic meter of air.

Even where levels are still high, though, any reduction in pollution improves health, said WHO's Sophie Gumy. And any efforts to curb air pollution helps combat climate change, as both are driven by emissions from waste burning and fossil fuel usage.

Edited by: Sarah Steffen and Gianna Grün

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