The 2023 World Air Quality report is in, and it reveals that far too many major cities are severely polluted.

Densely populated major cities are confronted with greater concentrations of unhealthy air and must contend with multiple challenges: a greater abundance of potential air pollutants, a lack of regulations and enforcement, overburdened infrastructure—and a larger, often growing, populace affected. For residents in the top five listed cities, poor air quality was a near-daily occurrence in 2023, with some cities often ranking among the most polluted year after year.

Below are listed major cities grappling with severe air quality issues, along with their sources of pollution, and a selection of the most polluted big cities in each other region.

Over 80 million people live in the major cities outlined here. And millions more individuals experienced frequent exposure to poor air quality in 2023.

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5. Kolkata, India

Kolkata, home to over 15 million residents, recorded an annual average PM2.5 concentration of 47.8 µg/m³ in 2023. The main sources of pollution in Kolkata include vehicle emissions, industrial activities, and domestic burning of biomass. Traffic congestion and older vehicles significantly contribute to air pollution, while various industries around and within the city elevate PM2.5 levels. Additionally, the use of biomass for cooking and heating exacerbates air quality issues.

Kolkata has recently introduced electric buses and stricter pollution controls for industries to combat air pollution, aiming to improve air quality over time.

4. Karachi, Pakistan

Karachi, a major metropolitan area in Pakistan, grapples with significant air quality issues. In 2023, the city’s average annual PM2.5 concentration was 56.4 µg/m³.

Karachi's pollution stems from vehicle emissions, industrial activities, and natural dust storms, contributing to health problems among its over 17 million residents. High numbers of older vehicles and lax emission standards worsen air quality, while numerous factories emit pollutants without adequate filtration. Rapid development and the natural arid climate increase airborne dust particles.

Karachi is working on initiatives to monitor and improve air quality, including increasing green spaces and enhancing waste management to reduce open burning.

3. Dhaka, Bangladesh

Dhaka, home to over 10 million residents, is the capital and most populous city of Bangladesh. The city recorded an average annual PM2.5 concentration of 80.2 µg/m³ in 2023, more than 16 times the WHO's recommended level. This marks a significant increase from 2022’s average of 65.8 µg/m³. During some months, PM2.5 levels exceeded 150 µg/m³, indicating severe air pollution.

The main sources of pollution include brick kilns, vehicle emissions, and other factors such as surface dust, factories, household cookstoves, plastic trash incineration, and unlined landfills. Many brick kilns operate illegally, contributing heavily to air pollution despite laws intended to restrict their locations. To address this, the Ministry of Environment, Forest, and Climate Change plans to use a brick kiln tracker to enforce regulations and reduce pollution at the source.

Dhaka’s government acknowledges the severity of air pollution from brick manufacturing and, despite challenges in enforcement, aims to regulate and curb significant pollution sources with the introduction of new technology. Comprehensive strategies and effective implementation of control measures are urgently needed to safeguard public health.

2. Lahore, Pakistan

11,021,000 people reside in Lahore, Pakistan’s capital and largest city. That means that over 11 million people were exposed to an average annual PM2.5 concentration of 99.5 µg/m3 in 2023 – hazardous levels of poor air quality that pose a significant risk to human health.

Lahore was the most polluted city in the world in 2022. The city’s thick smog, fueled by crop burning in Punjab Province, vehicle emissions, and brick kiln smoke, has sparked grassroots activism to increase air quality monitoring across the country. Despite these types of efforts, significant hurdles remain in mitigating pollution sources.

Screenshot of poor air quality in Lahore, Pakistan taken April 9, 2024. Source: IQAir Map.

Screenshot of poor air quality in Delhi, India. Source: IQAir Map.

1. Delhi, India

Delhi, India is a mega-city home to over 29 million people and is the second largest city on Earth. In 2023, the city’s average annual PM2.5 concentration was 102.1 µg/m3, a significant increase from the 2022 average of 93 µg/m³. Delhi was the fourth most polluted large city in the world in both 2021 and 2022, meaning that air quality continues to worsen.

Delhi air pollution is frequently hazardous due to regional crop burning, vehicle pollution, coal-powered plants, and landfill fires.

Most polluted regional cities

Poor air quality was a global problem in 2023, impacting nearly every region.

Outside of South and Central Asia, the most polluted major city was Hotan, China with an average annual PM2.5 concentration of 87.3 µg/m3.

Ras Al Khaimah, UAE, whose average annual PM2.5 was 52 µg/m3, finds air quality frequently impacted by desert sandstorms.

As in previous years, PM2.5 concentrations remained high in Africa and Asia. South Tangerang, Indonesia, neighbor to the capital city Jakarta, had an average annual PM2.5 concentration of 71.7 µg/m3, while Benomi, South Africa lying near Johannesburg and Pretoria, was 54.9 µg/m3 in 2023. Those PM2.5 concentrations made each city the most polluted major cities in Southeast Asia and Africa, respectively.

The most polluted major cities in the Americas in 2023 were in Mexico and Canada.

Guadalajara, Mexico was the most polluted major city in Latin America & Caribbean and had an average annual PM2.5 concentration of 25.8 µg/m3. Edmonton, Canada, a city frequently subjected to smoke from the extreme 2023 Canadian wildfire season, became the most polluted Northern America major city at an average annual PM2.5 concentration of 16.6 µg/m3.

Europe’s most polluted city, Igdir, Turkey, had an average annual PM2.5 concentration 47.2 µg/m3.

In Oceania, Perth, Australia was the most polluted regional major city with 3.4 µg/m3. Though no amount of air pollution is safe, the city was within the World Health Organization’s air quality guideline of 5 µg/m3.

What you can do

Air pollution can affect millions of lives, but there are practical solutions. You can play a part in improving urban air quality:

• Contact your local representatives and advocate for better air quality – recommend legislation and ordinances to fight air pollution at its source.
• Make a difference in your own life. Cut back your own energy use and walk, bike or ride public transportation when feasible.
• Stay informed: download a free air quality app. When air quality is poor, limit your outdoor exposure, purify your indoor air or put on a high-quality face mask.
• Join the movement! Keep your community safe by becoming an air quality data contributor. The air quality data you provide your community helps further air pollution education and empowers others to protect themselves from poor air quality.

The takeaway

We can only fully appreciate how dangerous air pollution is for city dwellers when cities are equipped with reliable air quality data. There remain significant gaps in air quality data for regions like Africa, West Asia, and Latin America and the Caribbean.

Global, real-time access to air quality data is a critical component in informing people about poor air quality, being equipped to act on poor air quality days, and taking informed steps to reduce air pollution at its source. More lives can be saved and health outcomes improved when people the world over know what’s in their air.