How megacities fight air pollution

Air pollution kills millions of people every year, especially in the world’s largest cities. But things can improve! DW magazine has compiled an overview of how megacities around the world managed to improve air quality—and, consequently, the quality of life for their residents—between 2017 and 2022.

Air pollution is a major problem worldwide—according to the World Health Organization (WHO), it contributes to about 7 million deaths each year. Residents of the world’s largest cities, from Delhi and Istanbul to Los Angeles, are among the most affected. However, last year’s analysis by the news portal DW brings surprisingly encouraging news: in many megacities, air quality is slowly improving.

The analysis focused on one key pollution indicator—PM 2.5, which refers to fine particulate matter composed of various solid particles and liquid droplets measuring 2.5 micrometers or smaller, much smaller than the average human hair. This indicator is often used as a measure of overall pollution levels.

“The smaller these particles are, the deeper they can penetrate into the body,” explains Sophie Gumy from WHO’s Climate, Environment, and Health Department. PM 2.5 particles are so small that they can enter the lungs and bloodstream, causing respiratory problems, heart disease, and lung cancer. In cities, these particles primarily come from vehicle emissions. Pollution is also contributed by solid fuels such as coal, wood, or kerosene used for heating and cooking, as well as industrial emissions and waste burning.

To determine how pollution levels have changed in recent years, DW analyzed data from the Swiss company IQAir, which produces air quality monitoring products and collects PM 2.5 concentration data in cities with more than 10 million inhabitants. Out of 25 megacities for which data was available, nearly all (21 cities) recorded an improvement in air quality over the analyzed period. What measures are they taking to achieve this?

1. Clean transport

To effectively tackle air pollution, cities are implementing various strategies. In many of them, transport plays a key role. Successful measures focus on reducing the number of cars, promoting walking and cycling, and expanding public transport. For example, Bangkok is expanding its still limited Skytrain and metro lines, while Delhi has set a goal to electrify 80% of its bus fleet.

Bike sharing in Mexico City

Zoe Chafe, Technical Lead for Air Quality at the C40 network, which helps nearly a hundred member cities become more environmentally friendly, told DW that many of these cities are also experimenting with low-emission zones. These are areas where only certain vehicles—or none at all—are allowed, and streets are often redesigned to provide more space for pedestrians and cyclists. “This is an issue that resonates across all regions of the world, and it’s really fantastic,” Chafe said.

2. Industrial sources

Another key factor that needs to be addressed is industry. For example, Delhi’s action plan against air pollution also focuses on reducing dust from construction activities and transitioning to cleaner fuels and more efficient technologies. However, the city remains one of the most polluted places on the planet, especially during the winter months. In 2024, the smog situation worsened to the point that authorities had to close schools. Despite this, Delhi managed to reduce pollution levels by 15% between 2017 and 2022. One major factor may have been the shutdown of the Badarpur coal power plant in 2018, which is estimated to have been responsible for about 10% of particulate air pollution in Delhi alone.

Pollution in Delhi

3. Waste management

Where waste is not properly collected and disposed of, people often burn it in open fires. This creates toxic smog and contributes to air pollution. This means that regulations and infrastructure for waste management must be part of every city’s plan against air pollution. Even where laws exist, progress can be slow. “There are solid waste management regulations from 2016, but they are still not implemented,” Bhavreen Kandhari told DW. The founder of the activist group Warrior Moms has been fighting for cleaner air across India for more than 20 years, submitting petitions to the government and courts.

4. Clean energy

When measures are consistently implemented, their impact can be significant. Chinese cities have drastically reduced air pollution levels in recent years. This is the result of what the Chinese government calls the “war on air pollution”, a set of measures targeting all major sources. This includes energy consumption for heating and electricity generation. For example, Beijing imposed strict emission limits on household boilers and offered subsidies to households that switched from coal-fired boilers to gas or electricity. One study concluded that the reconstruction of these boilers accounted for a 20% reduction in air pollution in Beijing.

Solar panel powering the traffic light in Shanghai

Outside of China, countries around the world are investing in renewable energy, gradually moving away from coal, and seeking alternatives to wood and coal used for cooking and heating. Seoul, the capital of South Korea, switched to gas heating back in the 1990s and is now considering more environmentally friendly alternatives, such as heat pumps.

What are the main challenges cities face?

Better data

When cities want to improve air quality, the first step is often better data collection. In Pakistan, for example, there are still very few official government monitoring stations, making it difficult to assess whether air quality is improving. But people like Abid Omar, founder of the Pakistan Air Quality Initiative in 2016, are trying to change this. “Individuals, companies, and like-minded organizations have come together and use low-cost monitors, publishing the data online,” he told DW. “It is precisely this data that raises awareness.”

Financing

According to Zoe Chafe from C40, financial resources are key to making real improvements in air quality. “Beijing was able to invest huge sums into the air quality problem,” she said. “And this is a fundamental question for many other cities: Do they have the money to take such a major step in improving air quality?” In recent years, China has invested more than 20 billion yuan annually in air pollution control—several billion dollars.

Collaboration

Air pollution can travel long distances and cross national borders. This is true, for example, in India, where post-harvest crop burning in northern states causes severe smog in Delhi and surrounding areas every year. Similar problems occur in the Nile Delta around Cairo, Egypt, or in Indonesia, where smoke from controlled agricultural fires reaches neighboring Singapore and Malaysia.

Crop burning in Vietnam

“So cities, regions, and countries will need to cooperate to achieve change,” Chafe said. “At the heart of the matter is human health. It doesn’t matter where the air pollution comes from—it is extremely important that it is reduced,” she added. Most major cities around the world still significantly exceed WHO limits for air pollution. There is still much to be done: air pollution levels in nearly all cities worldwide continue to exceed the WHO guideline of 5 micrograms per cubic meter of air.

Even in places where levels remain high, any reduction in pollution improves health, Sophie Gumy from WHO noted. Efforts to reduce air pollution also help combat climate change, since both problems are caused by emissions from waste burning and the combustion of fossil fuels.

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