Kiera Jefferson
Air pollution is a pressing global crisis that poses severe risks to the environment and human health. It is primarily caused by the burning of fossil fuels, vehicular emissions, industrial activity, construction dust, crop burning, and poor waste management. According to the World Health Organization (WHO), air pollution kills approximately 9 million people worldwide annually, with 99% of the world's population living in areas with air quality that exceeds safe limits. This article will explore the most polluted cities in the world, the sources of their pollution, and the health and environmental impacts they face.
| Characteristics | Values |
|---|---|
| Date of Data | 2024-2025 |
| Source of Data | IQAir, Earth.Org, Smart Air, Oizom |
| Number of Cities Assessed | 5,390 |
| Number of Countries Assessed | 63 |
| Number of Cities in Top 10 Polluted Cities List | 10 |
| Top 10 Polluted Cities | New Delhi, Greater Noida, Noida, Ghaziabad, Faridabad, Gurgaon, Bhiwadi, Patna, Sonipat, Muzaffarnagar |
| Country with Most Cities in Top 10 Polluted Cities List | India (all 10) |
| Top 5 Polluted Countries | Bangladesh, Pakistan, India, Bahrain, Nepal |
| Major Causes of Pollution | Fossil fuel use, vehicular emissions, industrial activities, agriculture, poor waste management |
| Health Impacts | Respiratory conditions, cardiovascular diseases, lung cancer |
| Environmental Impacts | Acid rain, eutrophication, climate change |
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What You'll Learn
New Delhi, India: the world's most polluted city
New Delhi, India's capital, is the world's most polluted city. The air pollution in New Delhi is so severe that it kills 2 million Indians annually and causes severe neurological, cardiovascular, and respiratory diseases, lung capacity loss, and even cancer. The city's air quality index (AQI) is consistently high, with an annual average of 91.6 μg/m³ in 2024, which is nearly unchanged from 92.7 μg/m³ in 2023. This is more than 10 times the World Health Organization's (WHO) annual PM2.5 guideline value of 5 μg/m³.
The hazardous air quality in New Delhi is due to a combination of unfavourable meteorological conditions, vehicular emissions, paddy-straw burning, firecrackers, and other local pollution sources. The problem is further exacerbated during the winter months when the air quality deteriorates to hazardous levels. The dense smog that envelops the city during this time has led the region's chief minister to declare a "medical emergency", forcing schools to shut down and visibility on the streets to drop to as low as 50 meters.
The impact of the pollution on the residents of New Delhi is profound. One resident, Shahbaz, described the situation as "death in the air," and shared how he struggles to breathe and has a constant cough. His wife, Noor, had to spend a night in the hospital due to "excessive itching" in her watery eyes. Another resident, Sheikh Ali, a 67-year-old rickshaw puller, described how the pollution has worsened in Delhi, causing a burning sensation in his chest.
While local and national governments have implemented measures such as sprinkling water and capping vehicle entry into cities, these are seen as temporary solutions that do not address the root causes of the worsening pollution. Environmentalists and advocates for cleaner air, such as Bhavreen Khandari, co-founder of Warrior Moms, lament the loss of festive winter traditions and the constant fear that the gloomy skies now evoke. The social divides in this already unequal society are amplified by the pollution crisis, as residents from different socioeconomic backgrounds cope with its effects in vastly different ways.
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Lahore, Pakistan: highest PM2.5 levels
Lahore, Pakistan's second-largest city, is considered the most polluted city in the country, with high levels of atmospheric particulate matter frequently exceeding World Health Organization (WHO) guidelines and national air quality guidelines. The dominant sources of Lahore's air pollution are primary emissions from local sources, with local emission sources contributing to approximately 57% of the city's air pollution. The most abundant species in the identified mass of PM2.5 were carbonaceous compounds, followed by ionic species such as SO42−, NO3−, Cl−, and NH4+.
The high levels of air pollution in Lahore have attracted significant attention due to their adverse effects on climate, visibility, and, most importantly, human health. For example, sulfate and nitrate in PM2.5 can significantly impact light scattering capacity. Furthermore, the air quality within Pakistan's major urban environments has been evaluated using portable equipment, which revealed that the PM2.5 concentration in Lahore varies between 72 μg·m−3 and 500 μg·m−3, with an average value of 286 μg·m−3.
The chemical composition and sources of atmospheric particulate matter in Lahore have been investigated to effectively mitigate the city's pollution. Comprehensive analyses of PM2.5 concentration and composition, meteorological conditions, PM2.5 sources, and fossil fuel consumption have been conducted to understand the affecting factors of PM2.5 pollution in Lahore better. These analyses revealed that primary organic carbon dominated secondary organic carbon, and mixed-source burning in industries such as brick kilns aggravated Lahore's air quality.
Controlling emissions from industry, transportation, and power plants would immediately help mitigate PM2.5 pollution in Lahore. Additionally, the fuel consumption situation in Pakistan was examined to identify the major contributing sectors to air pollution further. While local emission sources were the main contributors to Lahore's air pollution, there was also a contribution from the western states of India.
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India's pollution monitoring networks
India's air pollution problem is well-documented, with several of its cities featuring on lists of the world's most polluted locations. In 2019, the Indian government launched the National Clean Air Programme (NCAP) to address this issue in 131 cities. The NCAP involves conducting source apportionment studies and establishing emission baselines. As of February 2023, only 39 cities had completed these studies.
The NCAP cities were grouped into 104 airsheds, representing 164 cities and 21% of the national population. Four airsheds—Delhi, Mumbai, Indore, and Chandigarh—contain 10, 8, 5, and 5 cities, respectively. To effectively monitor and improve air quality, a total of 2118 sampling sites are recommended for these airsheds.
Cities can enhance their monitoring networks by combining regulatory monitoring with low-cost, high-density sensor networks. This hybrid approach can provide more comprehensive data for airshed-level air quality management plans. Additionally, consolidating information on emission sources is crucial for optimizing clean air efforts under the NCAP.
The Central Pollution Control Board, under the Ministry of Environment, Forest and Climate Change, plays a crucial role in monitoring air quality. They identify four key air pollutants for regular monitoring: Sulphur Dioxide (SO2), Oxides of Nitrogen as NO2, Respirable Suspended Particulate Matter (RSPM/PM10), and Fine Particulate Matter (PM2.5). Meteorological parameters such as wind speed, direction, relative humidity, and temperature are also integrated into the monitoring process. The frequency of monitoring is twice a week, with varying sampling frequencies for different pollutants, to gather 104 observations annually.
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Fossil fuels and vehicular emissions
Fossil fuels are formed from the decomposition of carbon-based organisms that died millions of years ago. These fossil fuels are extracted and burned for energy, and they are also used in the creation of plastics, steel, and a wide range of other products. There are three types of fossil fuels: coal, oil, and natural gas. The burning of these fuels releases large amounts of carbon dioxide and other greenhouse gases, which contribute to global warming and climate change. In 2018, 89% of global CO2 emissions came from fossil fuels and industry.
Vehicular emissions are a significant contributor to air pollution, particularly in the case of cars, trucks, and buses powered by fossil fuels. Transportation emits more than half of nitrogen oxides in the air, and is a major source of heat-trapping emissions. Vehicle exhaust contains pollutants such as particulate matter (soot), nitrogen oxides, and sulfur dioxides, which have been linked to adverse health impacts on nearly every organ system in the body. These emissions are also associated with the refining and distribution of fuels, as well as the manufacturing and disposal or recycling of vehicles.
To reduce air pollution from vehicular emissions, electric vehicles and buses are being introduced in cities, with commitments to transition to zero-emission transportation systems. Additionally, individuals can help by reducing the number of miles driven, carpooling, or using public transportation, walking, or biking instead of driving.
Nitrogen oxides and ammonia, which are emitted from burning fossil fuels, contribute to the formation of smog and acid rain. These emissions, along with excess greenhouse gases, pose health risks and negatively impact the environment, leading to algal blooms and oxygen-deprived aquatic zones that are toxic to aquatic life.
To address these issues, it is important to improve energy efficiency, transition to renewable energy sources, and reduce emissions from fossil fuel companies. The Paris Agreement of 2015 committed governments to reducing carbon emissions, but more action is needed to meet the goals of limiting global warming.
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Health and environmental impacts
Air pollution is a severe environmental threat to public health globally, impacting our health, development, and environment. According to the World Health Organization (WHO), 91.3% of countries and regions failed to meet safe air quality standards for PM2.5 pollution in 2024. PM2.5 refers to fine particulate matter that is smaller than 2.5 micrometers in diameter, which can be harmful when inhaled.
Health impacts of air pollution in highly polluted cities include respiratory conditions, such as asthma attacks, harm to lung development in children, and other lung diseases. It can also lead to cardiovascular diseases and lung cancer. The elderly, children, and people with pre-existing health conditions are especially vulnerable to the health effects of air pollution. In addition, air pollution can be deadly, with an estimated 7 million premature deaths globally each year attributed to air pollution, according to the World Health Organization.
Environmental impacts of air pollution include acid rain, eutrophication, and climate change. Acid rain can damage buildings, monuments, and natural environments, while eutrophication can lead to oxygen depletion in water bodies, harming aquatic life. Climate change, exacerbated by air pollution, increases the risk of wildfires, which further contributes to air pollution and harms ecosystems.
The major causes of air pollution in highly polluted cities include vehicle emissions, industrial activity, construction dust, crop burning, and poor waste management. These sources release pollutants such as nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), and particulate matter (PM) into the atmosphere, contributing to the degradation of air quality.
To address these health and environmental impacts, urgent action is needed to reduce air pollution. This includes implementing sustainable practices, transitioning to cleaner technologies, and improving waste management systems. Individuals can also take measures to protect themselves, such as checking air quality forecasts and reducing outdoor activities when air pollution levels are high.
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Frequently asked questions
According to a 2024 report, 126 out of 138 countries and regions exceeded the World Health Organization's (WHO) annual guidelines for PM2.5 concentrations. Central and South Asia host the world's top seven most polluted cities, with India being home to 13 of the 20 cities identified as the most polluted globally. The most polluted city in the world is Byrnihat, India, with New Delhi, the capital of India, coming in as a close second.
The major causes of air pollution in Indian cities include vehicle emissions, industrial activity, construction dust, crop burning, and poor waste management. The burning of fossil fuels to generate electricity and power vehicles is also a significant contributor to air pollution globally.
High air pollution can cause respiratory conditions, cardiovascular diseases, lung cancer, and stroke. It is especially dangerous for children and the elderly. According to the World Health Organization, about 9 out of 10 people are exposed to air pollution levels above the WHO's air quality guidelines.
Efforts like the Paris Agreement aim to combat air pollution by encouraging sustainable practices and cleaner technologies. Access to real-time pollution data is also crucial, as many countries, especially within Africa and the Middle East, lack this information. Stringent measures to reduce coal consumption, emissions from transportation, and the relocation of polluting heavy industries have proven effective in improving air quality.
