World's Most Polluted Cities: A Toxic Reality

Air pollution is a serious global health threat, causing increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections. According to the World Health Organization (WHO), 99% of people currently live in areas where the air quality exceeds safe limits. While air pollution is most prevalent in middle- to low-income countries, cities in the United States and other parts of the world also face significant air quality issues. This paragraph introduces the topic of the most polluted cities in the world, exploring the impact of air pollution on human health and the efforts needed to improve air quality.

India: 12 of the 15 most polluted cities in the world are in India

India is home to 12 of the 15 most polluted cities in the world. According to IQAir's 2021 World Air Quality Report, India's cities exceed the World Health Organisation's (WHO) guidelines for PM2.5 levels by 10 times. New Delhi, the capital, was ranked as the capital with the worst air quality in the world, with air quality 13.2 times higher than the WHO guideline limit. Other cities in India, such as Mullanpur, a town in Punjab, also face severe air pollution. In 2024, it was ranked the fourth most polluted city globally, with an average PM2.5 concentration of 102.3 µg/m³.

The main sources of air pollution in India include vehicular traffic, diesel generators, the burning of fossil fuels for cooking, industrial activities, waste burning, and agricultural practices such as crop burning. These sources contribute to high levels of particulate matter (PM2.5 and PM10) and nitrogen oxides, which can form smog and pose significant health risks.

The effects of air pollution in India are dire, with an estimated 1 million deaths attributed to air pollution annually, according to The Lancet. The high levels of pollutants in the air increase the risk of stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections. Vulnerable groups, such as children, the elderly, and people with respiratory conditions, are at even higher risk of adverse health effects.

Despite the grim situation, there is some progress. India's air quality has improved in recent years, with more than half of its cities recording lower air pollution levels in 2021 compared to 2020. This improvement is attributed to stringent measures to reduce coal consumption, emissions from transportation, and the relocation of heavy industries. Additionally, India has pledged to become carbon neutral by 2060, which demonstrates a commitment to addressing the issue further. However, continued and urgent efforts are needed to ensure cleaner and safer air for India's residents, especially in the most polluted cities.

Air pollution: caused by vehicular traffic, diesel generators, and the burning of fossil fuels

Air pollution is a pressing issue in many cities worldwide, with vehicular traffic, diesel generators, and the burning of fossil fuels identified as significant contributors.

Vehicular emissions have become a dominant source of air pollutants in many areas, including carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs), hydrocarbons (HCs), nitrogen oxides (NOx), and particulate matter (PM). The increasing severity and duration of traffic congestion exacerbate the problem, leading to higher pollutant emissions and degraded air quality, particularly near large roadways. This poses health risks to drivers, commuters, and individuals residing near these congested areas, with potential short-term and long-term health consequences.

Diesel generators have also been identified as a source of air pollution, particularly before the implementation of emissions regulations. However, tighter standards and industry innovations have significantly reduced their environmental impact. For example, the adoption of biodiesel, a renewable energy source with lower pollution levels than standard diesel, has led to decreased greenhouse gas emissions. Additionally, exhaust gas recirculation (EGR) systems in diesel generators tackle NOx emissions by lowering the combustion temperature.

The burning of fossil fuels, such as coal, gasoline, and diesel, has been linked to extreme air pollution and adverse health effects. A recent study found that air pollution from fossil fuels is responsible for approximately 8.7 million deaths globally in 2018, with China and India being the hardest hit. The combustion of fossil fuels contributes to fine particulate matter, known as PM 2.5, which has been associated with fatal lower-respiratory infections and other respiratory issues.

It is worth noting that while this response focuses on specific contributors to air pollution, other factors, such as industrial emissions and natural sources like dust and wildfires, also play a role in degrading air quality in cities worldwide.

Health risks: air pollution can trigger asthma attacks and cause respiratory illnesses

Air pollution is a major public health concern, causing approximately 9 million deaths worldwide annually, according to the World Health Organization (WHO). It is particularly prevalent in low- to middle-income countries due to poor pollution standards, industrial work, and development.

One of the most common air pollutants is ground-level ozone, which is formed by chemical reactions between emissions from burning fossil fuels, vehicles, power plants, and factories, combined with sunlight and heat. This ground-level ozone is a primary component of smog, which poses higher risks of respiratory illnesses, including triggering asthma attacks and worsening symptoms for those with asthma or chronic obstructive pulmonary disease (COPD). The smallest airborne particles, known as PM2.5, are the most dangerous as they can penetrate deep into the lungs and even enter the bloodstream. These particles are commonly found in haze, smoke, soot, and airborne dust, causing serious air quality issues.

In cities with high levels of air pollution, individuals with asthma should take extra precautions, such as monitoring pollution levels and limiting time outdoors when pollution is severe. They may also need to increase their medication during periods of high pollution. Poor air quality can irritate the airways, causing swelling and tightening, and making it harder to breathe. Additionally, pollutants can increase the likelihood of respiratory infections, which can further trigger asthma symptoms.

While the causal relationship between air pollution and the development of adult asthma is not yet conclusive, exposure to outdoor pollutants, including ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and particulate matter, has been linked to increased asthma symptoms, exacerbations, and hospitalizations. Children are particularly vulnerable, with traffic-related air pollution, nitrogen dioxide, and second-hand smoke exposures identified as significant risk factors for asthma development.

To address air pollution and its health impacts, some countries have implemented stringent measures to reduce coal consumption, transportation emissions, and the presence of polluting heavy industries. Access to real-time pollution data is also crucial for individuals and communities to make informed decisions and take protective actions, especially in highly polluted areas.

PM2.5 concentration: the higher the concentration, the worse the air quality

PM2.5 refers to particulate matter that is 2.5 microns or less in diameter. It is a complex mixture of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. These particles are so small that they can be inhaled deep into the lungs, which can induce adverse health effects. The higher the concentration of PM2.5 in the air, the worse the air quality and the greater the health concern.

The World Health Organization (WHO) has established National Ambient Air Quality Standards for PM2.5. The short-term standard (24-hour or daily average) is 35 micrograms per cubic meter of air, while the long-term standard (annual average) is 9 micrograms per cubic meter of air. When the concentration of PM2.5 exceeds these standards, it is considered unhealthy air quality, and the health risks increase as the concentration rises.

The U.S. Environmental Protection Agency (EPA) uses the Air Quality Index (AQI) to communicate about outdoor air quality and health. The AQI values correspond to the level of air pollution and health concerns, with higher values indicating greater pollution and risk. An AQI value of 50 or below represents good air quality, while a value over 300 represents hazardous air quality. When the AQI value is above 100, the air quality is considered unhealthy, first for sensitive groups and then for everyone as values climb higher.

According to IQAir's 2021 World Air Quality Report, 12 of the 15 most polluted cities in the world are in India. New Delhi was ranked as the capital with the worst air quality, with PM2.5 levels 13.2 times higher than the WHO guideline limits. India's high pollution levels are attributed to vehicular traffic fumes, diesel generators, the burning of fossil fuels for cooking, industrial activities, waste burning, and agricultural practices.

It is important to note that air pollution from burning fossil fuels, such as coal, oil, and gas, has severe health impacts worldwide. The WHO estimates that nearly 9 million people die prematurely each year due to air pollution from these sources. Therefore, it is crucial to prioritize reducing air pollution and improving air quality to protect public health and reduce mortality and morbidity associated with air pollution.

Real-time data: many countries lack access to real-time pollution data, which is needed to address the issue

Air pollution is a significant global issue, with 99% of people worldwide breathing air that exceeds the World Health Organisation's (WHO) guideline limits. The burning of fossil fuels, vehicular traffic, industrial work, and development are major contributors to poor air quality. According to IQAir's 2021 report, 12 of the 15 most polluted cities are in India, with New Delhi ranked as the capital with the worst air quality.

Addressing air pollution requires accurate and timely data, yet many countries lack access to real-time pollution information. This is particularly true for nations in Africa and the Middle East. The lack of real-time data hinders the ability to monitor and address pollution sources effectively. Real-time data is essential for keeping industrial facilities and other polluters accountable and empowering local authorities, community members, and stakeholders to take action. For instance, access to such data can enable communities to work with corporate responsibility teams or partner with local environmental authorities to implement emissions reduction initiatives.

Furthermore, real-time data improves local and national air quality forecasts. NASA's Land, Atmosphere Near-real-time Capability for Earth Observation (LANCE) provides near-real-time data that helps air quality forecasters make more accurate predictions. These forecasts are valuable tools for the public, as they can choose to limit their outdoor activities during periods of poor air quality, thereby reducing their exposure to harmful pollutants.

The advent of affordable and accessible technologies, such as low-cost sensors, has democratized air quality measurement. Platforms like Clarity's OpenMap and the OpenAQ platform provide open access to real-time air quality data, filling the gap left by government data limitations. According to OpenAQ's 2020 Global State of Play report, countries with the worst air quality tend to have the least access to air quality data. This underscores the importance of independent data collection and dissemination platforms.

In conclusion, real-time pollution data is a critical tool in the fight against air pollution. By providing access to this data, communities, authorities, and stakeholders can make informed decisions and take targeted actions to improve air quality and protect public health.

Frequently asked questions