Helena Joyce
Air pollution is a pressing global issue that impacts the health and well-being of millions worldwide. According to the World Health Organization (WHO), air pollution from fossil fuel burning and other sources contributes to nearly 9 million deaths annually. While air pollution is a pervasive problem, some cities are more affected than others. As of 2025, New Delhi, India, ranks as the most polluted city, with other Indian cities also featuring prominently on the list. However, the focus of this discussion is on the second most polluted city in the world, and the factors contributing to its poor air quality. With an increasing awareness of the health and environmental hazards posed by air pollution, understanding the situation in the second most polluted city becomes crucial for driving change and implementing effective solutions.
| Characteristics | Values |
|---|---|
| Second Most Polluted City in the World | Delhi, India |
| Annual PM2.5 Level | 108.3 µg/m³ |
| AQI Concentration | 169 ('Unhealthy' category) |
| Pollution Causes | Vehicular traffic fumes, diesel generators, burning of fossil fuels for cooking, industry, burning of waste, farmers setting fields alight after harvest |
| Other Highly Polluted Cities | Byrnihat, India; Karaganda, Kazakhstan; Dhaka, Bangladesh; Ouagadougou, Burkina Faso; Dushanbe, Tajikistan; Baghdad, Iraq |
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What You'll Learn
Hotan, China
Hotan, an ancient city in China, was ranked as the most polluted city in the world in 2020, with a PM 2.5 reading of 110.2µg/m3. This level of air pollution poses serious health risks, as the particles are large enough to enter the bloodstream.
Hotan is a major oasis town in the autonomous region of Xinjiang, in northwestern China. With a population of around 400,000-5,000,000 people, it is situated in the Tarim Basin, just north of the Kunlun Mountains, and is surrounded by deserts and mountain passes. The town has a rich history, dating back to the ancient Silk Road, and has long been an important commercial and cultural centre. It was once the capital of the ancient Kingdom of Khotan, one of the earliest Buddhist states in the world, and a bridge for the transmission of Buddhist culture from India to China.
The city's strategic location has made it a bustling hub of trade and cultural exchange for centuries. Marco Polo visited in 1274, noting its wealth of agricultural produce and importance as a trading centre. Hotan has been famous for its fine fabrics, silks, and cotton, as well as its metalwork and jewellery. The area is also a source of alluvial gold and jade.
However, Hotan's past and geographical location have also contributed to challenges such as poverty and unemployment. The availability of cheap labour attracted industries, leading to rapid industrialization and a subsequent increase in air pollution. The construction of new road networks has further intensified traffic, particularly industrial vehicles.
Despite these issues, the Chinese government has taken steps to address air pollution through the Air Pollution Program. This initiative aims to reduce air pollutants and carbon emissions, with a $1.3 million investment successfully lowering carbon emissions by 2.5 million per year.
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Air Quality Index (AQI)
The Air Quality Index (AQI) is a tool used to communicate information about outdoor air quality and health. The AQI includes six colour-coded categories, each corresponding to a range of index values and a different level of health concern. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality.
The AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is unhealthy: at first, for certain sensitive groups of people, then for everyone as AQI values increase. The EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act. Each of these pollutants has a national air quality standard set by the EPA to protect public health.
AirNow.gov is a website that provides air quality data for local areas, as well as at the state, national, and world views. It offers interactive maps, such as the Fire and Smoke Map, which show the impact of wildfire smoke on air quality in different states. The website also provides resources like AQI calculators, activity guides, and air quality alerts for teachers, students, and health professionals.
The World Health Organization (WHO) also maintains a database of air pollution monitoring results from thousands of towns and cities worldwide. This database represents air quality by the annual mean concentration of particulate matter (PM10 and PM2.5), providing a global perspective on outdoor air pollution.
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Industrial growth and sandstorms
Sand and dust storms are a natural phenomenon that occurs when strong winds meet bare or dry soil, lifting large amounts of sand and dust into the atmosphere. These storms can have severe impacts on human health and welfare, the environment, and industry.
The main sources of these mineral dust storms are dry regions in Northern Africa, the Arabian Peninsula, Central Asia, and China. Australia, America, and South Africa also contribute to a lesser extent. Human activities such as deforestation, overgrazing, and the overuse of water are causing deserts to spread and increasing the likelihood of sand and dust storms. These storms affect some 330 million people worldwide, from Sub-Saharan Africa to Northern China and Australia. The United Nations has designated July 12 as the first International Day of Combating Sand and Dust Storms to raise awareness and spur international efforts to counter them.
Industrial growth and development have been identified as significant contributors to air pollution, which is closely linked to the occurrence of sand and dust storms. The burning of fossil fuels in power plants and vehicles releases air pollutants, emissions, and chemicals into the atmosphere. These pollutants, including nitrogen oxides, react with ultraviolet radiation from the sun to form smog, which poses higher risks of respiratory illnesses. Poor pollution standards and industrial work, particularly in middle- to low-income countries, exacerbate the issue.
The impact of industrial growth on sand and dust storms is evident in the Mongolian Plateau, where the flourishing mining industry has adversely affected surface vegetation and the ecological environment. The rapid increase in coal output has altered the spatial and temporal distribution patterns of spring sand and dust storms in the region. Both the Mongolian and Chinese governments have implemented measures to combat desertification and reduce the occurrence of sandstorm disasters.
To mitigate the effects of industrial growth on sand and dust storms, it is crucial to address the root causes. This includes reducing greenhouse gas emissions, restoring parched landscapes, and implementing sustainable land management practices. By taking proactive measures, countries can lessen the frequency and intensity of sand and dust storms, improving the health and welfare of affected communities and reducing economic losses.
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Air pollution health risks
Air pollution is the presence of one or more contaminants in the atmosphere, such as dust, fumes, gases, mist, odours, smoke, or vapours. These pollutants can enter the body through the respiratory tract, leading to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting the lungs, heart, and brain, ultimately leading to disease. Almost every organ in the body can be impacted by air pollution.
Fine particulate matter, such as PM2.5, is an important source of health risks as these particles can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage to tissues and cells. Short-term exposure to high levels of particulate matter can lead to reduced lung function, respiratory infections, and aggravated asthma. Long-term exposure increases the risk of stroke, heart disease, chronic obstructive pulmonary disease, and cancer. Children are especially vulnerable, with higher pollution levels causing short-term respiratory infections and increased school absences. Higher levels of air pollution are also associated with increased asthma prevalence in children, and those exposed to high levels of pollutants are more likely to develop bronchitis symptoms in adulthood.
Other health risks associated with air pollution include adverse pregnancy outcomes, such as low birth weight and small gestational age. A study of over 57,000 women found that living near major roadways may increase the risk of breast cancer. Additionally, occupational exposure to benzene, an industrial chemical, is linked to leukemia and non-Hodgkin's lymphoma. Nitrogen oxides have been associated with an increased risk of hemorrhagic stroke in post-menopausal women.
Air pollution also disproportionately impacts certain communities. People of colour are more likely to be exposed to air pollution and to suffer harm to their health as a result. This is due to systemic racism practices such as redlining and residential segregation, which have limited the ability of people of colour to build wealth and access safe and green living environments. Additionally, low-income communities are more likely to live in close proximity to sources of pollution and have fewer resources to relocate, making them more vulnerable to pollution-related health effects.
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Global air pollution crisis
Air pollution is a critical global issue that poses significant risks to public health, the environment, and economies worldwide. It is caused by a range of sources, including household combustion devices, motor vehicles, industrial facilities, forest fires, residential energy use, power generation, agriculture, waste incineration, and industry. According to the World Health Organization (WHO), nearly all of the global population (99%) breathes air that exceeds the recommended guideline limits for pollutant levels. This has severe consequences for human health and contributes to approximately 8.1 million premature deaths annually, surpassing tobacco as the leading cause of preventable deaths.
Outdoor and indoor air pollution are key contributors to the global disease burden, causing respiratory and other diseases. Fine particulate matter (PM2.5 and PM10), carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide are among the pollutants of major concern. These pollutants can lead to heart disease, stroke, lower respiratory infections, lung cancer, diabetes, and chronic obstructive pulmonary disease (COPD). The impact of air pollution extends beyond physical health, reducing the quality of life and average life expectancy worldwide by 2.2 years.
Low- and middle-income countries bear the brunt of the impact, with 9 out of 10 deaths attributed to outdoor air pollution occurring in these regions. This disparity is influenced by factors such as the use of polluting open fires or simple stoves for cooking, fueled by kerosene, biomass, or coal. However, air pollution does not discriminate solely based on income; it is a pervasive issue across all countries, with varying levels of severity.
The link between air pollution and climate change further exacerbates the crisis. Climate change intensifies the health impacts of allergens and airborne particles, creating a vicious cycle where air pollution and climate change worsen each other's effects. However, addressing air pollution presents a unique opportunity to tackle both issues simultaneously. Policies and interventions that promote sustainable land use, cleaner energy and transport, energy-efficient housing, and improved waste management can effectively reduce air pollution and mitigate climate change.
The WHO and other organizations have recognized the urgency of the situation and are actively working to address the global air pollution crisis. Initiatives such as providing technical support to member states, raising awareness about the risks, and implementing solutions to mitigate exposure risks are underway. Additionally, global, regional, and transboundary initiatives have been established to foster cooperation on air quality management, with countries like Colombia and Mali integrating air pollution considerations into their national climate plans. While progress has been made, with death rates from indoor air pollution showing a notable decline, the crisis demands continued attention and concerted efforts from governments, organizations, and societies to safeguard public health and the planet.
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Frequently asked questions
Dhaka, the capital of Bangladesh, is the second most polluted city in the world.
Dhaka exhibited an annual average PM2.5 concentration of 80.2 micrograms per cubic meter of air.
PM2.5 refers to particles smaller than 2.5 micrometers in the air.
Other cities that are among the most polluted in the world include Karaganda, Kazakhstan; Delhi, India; and Byrnihat, India.
The major causes of air pollution in these cities include fossil fuel use, vehicular emissions, industrial activities, agriculture, and poor waste management.
