Globally, air pollution is the most severe environmental threat to public health. Improving air quality will improve our health, development, and the environment. With every breath we take, we inhale small particles that can harm our lungs, hearts, and brains and create various other health issues. Additionally, the cities labelled as the “most polluted” often have dense populations, industrial activities, and vehicular congestion. Sometimes, geographical conditions also trap pollutants in these areas. Moreover, It is not confined to a specific region or a type of country; it permeates the skies of both developed and developing nations, with severe consequences related to urban air pollution.
The Top 10 Most Polluted Cities:
Rank | City | Country | AQI | PM2.5 Conc. |
---|---|---|---|---|
1 | Dhaka | Bangladesh | 389 | 79.9 µg/m3 |
2 | Lahore | Pakistan | 331 | 73.7 µg/m3 |
3 | Begusarai | India | 351 | 54.4 µg/m3 |
4 | Khujand | Tajikistan | 273 | 49.0 µg/m3 |
5 | Ouagadougou | Burkina Faso | 268 | 46.6 µg/m3 |
6 | Erbil | Iraq | 224 | 43.8 µg/m3 |
7 | Dubai | UAE | 213 | 43.0 µg/m3 |
8 | Kathmandu | Nepal | 212 | 42.0 µg/m3 |
9 | Cairo City | Egypt | 211 | 42.4 µg/m3 |
10 | Kinshasa | D. R. Congo | 205 | 40.8 µg/m3 |
It’s said that the air we breathe is the essence of life. However, for residents of the following cities, the air they breathe daily might be far from pure. Air pollution has become a primary global concern in the last few decades, leading to numerous health and environmental challenges. Here’s a look at the world’s top 10 most polluted cities and the pressing need for change.
1) Dhaka, Bangladesh
- The research team at the Center for Atmospheric Pollution Studies (CAPS) at Stamford University Bangladesh has observed the intensity of air and noise pollution during the English New Year celebrations for the past seven years.
- Dhaka’s rapid urbanization and population growth have strained its infrastructure. Alongside the dense traffic, brick kilns around the city release vast amounts of particulates. The city’s residents often wear masks, but the causing situation requires more substantial solutions.
- In the early hours of 2024, air pollution increased by about 64 micrograms to peak at 249 micrograms/m3, which is considered very unhealthy in the air quality index.
2) Lahore, Pakistan
- Unfortunately, Lahore, Pakistan’s bustling and historically significant city, is second on our ranking. Every winter, temperature inversion combines with crop burning, vehicle emissions, industrial pollution, and crop burning in the surrounding area, creating harmful smog conditions in Punjab Province.
- Punjab Province has banned crop burning, prioritized reforestation, and launched public transportation projects. Winter Residents frequently experience respiratory issues, highlighting the urgent need for appropriate legislation.
- Every city in Pakistan included in the 2023 report measured concentrations above 30 μg/m3, at least six times the recommended WHO annual PM2.5 guideline.
3) Begusarai, India
A new report on air quality in cities around the world has ranked Begusarai in Bihar as the most polluted in India and the world.
Why Begusarai?
There is nothing very special about Begusarai, located in eastern Bihar. It is not an industrial town and has no obvious source of local generation of pollutants. This is also true of the other Bihar towns on the most polluted list. So what makes Begusarai the most polluted of all? The bulk of these pollutants come from burning solid fuels. A study by a professor in the Department of Civil Engineering and Department of Sustainable Energy at IIT Kanpur said. “Solid waste burning could also be a major contributor,” he said.
Dr Tripathi, one of India’s most eminent experts on air pollution, said that despite the success of schemes such as Ujjwala in many parts of the country, many rural households may still be burning solid fuels for cooking.
4) Khujand, Tajikistan
- Khujand, also known as Khojand, is Tajikistan’s second-largest city. It is located in the Fergana Valley in the country’s north. Khujand is a historic city that dates back to the seventh century. It was previously a significant hub on the Silk Road trading route. The current concentration of PM2.5 in Khujand is 64 (µg/m³).
- The World Health Organization (WHO) recommends 15 µg/m³ as the threshold concentration of PM2.5 for 24 hrs. Currently, the concentration is 2.56 times the recommended limit. This is likely caused by industrial emissions, particularly from cement and power plants, along with vehicle exhaust as the city grows.
5) Ouagadougou, Burkina Faso
- According to World Health Organization recommendations, Burkina Faso’s air quality is dangerous. According to the most recent data, the country’s annual mean PM2.5 concentration is 46 µg/m3, exceeding the recommended maximum of 10 µg/m3. The increasingly contaminated ambient air quality monitoring focuses on pollutants that are of the greatest health concern to the population.
6) Erbil, Iraq
- The global threat of declining air quality compromises the well-being of all living things. Erbil has faced serious environmental degradation, like many other locations, due to urban expansion, automotive escalation, industrialization, and inadequate fuel consumption. While Erbil is a historic and modern city, air quality remains challenging.
7) Dubai, UAE
- In 2023, two West Asian countries, Iraq (43.8 μg/m3) and the United Arab Emirates (43.0 μg/m3), ranked among the ten most polluted countries in the world. Five of the region’s top eight most polluted cities are capital cities: Baghdad, Kuwait City, Manama, Abu Dhabi, and Doha. However, there was a reduction in the annual average PM2.5 concentrations for the nine most polluted cities in West Asia.
8) Kathmandu, Nepal
- Kathmandu is among the top 10 most polluted cities globally, with PM2.5 levels soaring to 154 micrograms per cubic meter.
- Air quality in the Kathmandu Valley has deteriorated to dangerous levels, prompting major public health concerns. Although declines in air quality are usual during the winter and dry seasons, a sudden increase in air pollution levels is concerning, according to public health specialists. The air quality will worsen as agricultural residue burning begins in the Tarai and dirty air from India enters the region.
9) Cairo City, Egypt
- Despite contributing to 33% of Egypt’s current GDP, pollution from traffic congestion, slash-and-burn land clearing, industrial electricity, and open waste burning threatens its long-term growth prospects.
- According to the World Bank, the region’s estimated economic cost of air pollution is around 2% of GDP annually.
- In Cairo, air pollution causes around 18,000 premature deaths or 16% of the annual total. A 2023 report by the Clean Air Fund warns that without key urban development interventions during this period, the economic cost of air pollution in six rapidly expanding urban cities – Accra, Cairo, Johannesburg, Lagos, Nairobi, and Yaounde could reach a total of $137.8 billion by 2040. Despite a 10.5% decrease in 2023, PM2.5 levels in Cairo continue to exceed the WHO annual PM2.5 guideline by more than eight times, with an annual average of 42.4 μg/m3.
- PM2.5 levels also rose by 10.3% in Accra, Ghana, with an annual average concentration of 33.2 μg/m3.
10) Kinshasa, Democratic Republic of the Congo.
Outdoor annual PM2.5 levels in the Democratic Republic of the Congo can exceed the WHO Air Quality Guideline, particularly in major centers like Kinshasa, which has over 11 million people. Most of the DRC’s population is also constantly exposed to harmful levels of indoor air pollution, as more than 90% of the population cooks with wood. In the Democratic Republic of the Congo, ambient and residential air pollution is estimated to kill over 32,000 people per year.
Air Pollution as a Global Issue
Firstly, Air pollution poses a significant global environmental threat to our health and food security. Every year, it is estimated that it causes approximately 3.7 million premature lives worldwide and damages enough crops to feed millions. The data represents 6.7% of total deaths worldwide and was the cause of 16% of lung cancer deaths, 11% of chronic obstructive pulmonary disease-related deaths, 29% of heart disease and stroke, and approximately 13% of deaths due to respiratory infection. Secondly, exposure to air pollution containing PM2.5 is closely associated with cardiovascular disease, as assessed in a large study from metropolitan areas. (Inhalation Toxicology Research Center, Korea Institute of Toxicology, Jeonbuk, Korea). The following are some key aspects of air pollution as a global concern:
Health Impacts:
- Air pollutants like particulate matter, ozone, nitrogen dioxide, and sulphur dioxide can exacerbate respiratory conditions like asthma, leading to cardiovascular diseases and premature death.
- Streptococcus pneumonia (pneumococcus) is the leading cause of pneumonia and bacterial meningitis. Several recent studies indicate an association between the incidence of pneumococcal disease and exposure to air pollution. (Beentjes et al, 2022,)
- Long-term exposure can cause lung cancer and developmental problems in children.
Environmental Impacts:
- Acid Rain: Caused by the release of sulphur dioxide and nitrogen oxides, which react with water vapour in the atmosphere. This can harm aquatic life, forests, and even buildings and monuments.
- Eutrophication: Nitrogen compounds from agricultural runoff and emissions can lead to nutrient pollution in water bodies, causing excessive algae growth and impacting aquatic life.
- Climate Change: Greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) trap heat in the atmosphere, leading to global warming.
Economic Impact:
- The health effects of air pollution result in increased medical costs and lost labour productivity.
- Damage to infrastructure and agricultural yield reductions can strain economies.
Global Variation:
- While air pollution is a global issue, its intensity varies. With rapid industrialisation and weaker emission standards, developing nations often face severe air quality challenges. For instance, cities in India and China frequently experience hazardous air quality.
Global Initiatives:
- Paris Agreement: An international treaty to combat climate change by limiting global warming to below 2°C.
- BreatheLife: A campaign led by the World Health Organization (WHO), Climate and Clean Air Coalition, and the United Nations Environment Programme, aiming to achieve safe air quality levels worldwide by 2030.
Methodology for Ranking Polluted Cities
Ranking the most polluted cities typically requires a systematic methodology that assesses various indicators of air quality. There are many effluents/pollutants present in the air that are harmful and cause diseases in humans which eventually lead to an increase in morbidity and mortality. Therefore, there is a need to identify those factors and evaluate the effect of pollution caused by air on the health of humans which is a prerequisite for the implementation of policies in preventing pollution.
Selection of pollutants:
- Typically, critical contaminants with serious health consequences are picked. Particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2), and carbon monoxide (CO) are among examples.
Data Collection:
- Air Quality Monitoring Stations: Cities with established monitoring networks have sensors placed at various locations to measure pollutant concentrations in real time.
- Data Aggregators: Organisations like the World Air Quality Index project gather and present data from different sources.
Temporal Assessment:
- It’s vital to assess pollution over different periods: daily, monthly, seasonally, and annually. This accounts for variations due to festivals, agricultural burning seasons, or climatic conditions.
Calculation of Air Quality Index (AQI):
- AQI is a standardised index to communicate how polluted or dirty the air will become. It’s calculated using the concentrations of selected pollutants.
- Each country might have its own AQI system, but there are also globally accepted metrics, like the one proposed by the World Health Organization (WHO).
Other Factors:
- While air quality is the primary factor, some rankings consider water pollution, waste management, and other environmental aspects to provide a comprehensive environmental assessment.
Data Validation and Verification:
- Ensuring that the data is reliable and accurate is crucial. This might involve cross-referencing between different sources or ground-truthing.
Explanation of the Criteria and Data Sources Used for Ranking the Cities
Typically, precise criteria relating to the concentration of pollutants and the sources of data available are used to rank cities according to their levels of air pollution. Some standard criteria and data sources are used to rank the cities.
Ranking Criteria:
Concentration of Key Pollutants:
- Particulate Matter (PM2.5 and PM10): Fine particles suspended in the air that can penetrate deep into the lungs and reduce visibility.
- Ozone (O3): Ground-level ozone is a harmful air pollutant formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight.
- Nitrogen Dioxide (NO2): Often associated with traffic and combustion processes.
- Sulfur Dioxide (SO2): Typically originates from burning fossil fuels like coal or oil.
- Carbon Monoxide (CO): Primarily from the incomplete combustion of fossil fuels.
Air Quality Index:
- Environmental agencies have been using the air quality index (AQI) to evaluate data and inform the public about the health effects of air pollution. One can use air quality monitors to monitor air quality in real time. This way, one can constantly have air quality updates and take immediate mitigation measures.
Threshold Limits:
- Government agencies with environmental engineers have set the threshold limits, which should be at a safe threshold. For example, An AQI value of 100 typically represents the ambient air concentration for each pollutant for the protection of public health. AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is unhealthy.
Data Sources:
Ground-based Monitoring Stations:
- Many cities and countries have established networks of air quality monitoring stations. These stations provide real-time data on various pollutants.
Government Reports:
- National such as (CPCB) or regional (SPCB) environmental agencies often release annual or quarterly reports detailing air quality status, which can be a source of data for rankings.
Research & Studies:
- Academic institutions, NGOs, or research organisations may conduct studies or deploy sensors, providing additional or more granular data on air pollution in specific areas.
1. Use of Air Quality Monitoring Stations:
Air quality monitoring system refers to gathering and analysing samples of ambient air pollution. To assess the condition of the air, data from these samples are compared to clean air standards, historical data on air quality levels, and data on its effects on human health and the environment. First, let us understand the monitoring needs:
Identifying the purpose behind the monitoring of air quality:
- Your monitoring requirements could include tracking indoor pollution levels in your home or workplace, determining the outdoor air quality for environmental projects, or adhering to industrial safety rules. Your options might be significantly reduced by defining your unique needs.
Which types of pollutants do you want to monitor:
- The EPA created National Ambient Air Quality Standards (NAAQS) for six common air pollutants, sometimes called “criteria” air pollutants, to safeguard human health and welfare across the country. The contaminants are particulate matter, ozone, carbon monoxide, sulphur dioxide, nitrogen dioxide, and lead.
2. Measurement of pm2.5 and PM10 Levels:
Particulate matter (PM) from the atmosphere is a significant air contaminant that contributes to the deterioration of air quality. Environmental protection authorities worldwide regularly measure and monitor PM2.5 and PM10 as part of regulation measurements. Numerous health problems, including allergic reactions, lung dysfunction, cardiovascular disorders, malignancies, etc., can be made worse by air pollution. (Pope et al., 2021). Moreover, In the last decade, PCBs have established real-time ambient air-quality monitoring stations (Continuous Ambient Air Quality Monitoring Stations, CAAQMS) in most of the urban locations in India.
Gravimetric Method:
- This is the standard method for measuring PM concentrations.
- Ambient air is drawn through a filter for a specific duration. Particles from the air are collected on the filter.
- The filter is weighed before and after the sampling to determine the mass of the collected particles.
- The concentration (usually in µg/m3) is calculated based on the volume of air sampled.
Optical Methods:
- Devices like nephelometers or light-scattering photometers measure the scattering of light caused by particles in the air.
- The amount of light scattered is related to the concentration and size of the particles.
- While they provide real-time data, they may require periodic calibration with gravimetric methods to ensure accuracy.
IoT Sensors:
- There’s a growing market for compact, low-cost, robust new technological PM sensors.
- Many use optical methods but in a more compact form.
- They’re great for city-level, industrial-level monitoring or community monitoring.
3. Other Relevant Environmental Data:
Toxics and Heavy Metals:
- Elements like lead, mercury, and cadmium can sometimes be part of air quality considerations, especially in areas with specific industrial activities.
Meteorological Data:
- Weather conditions influence pollutant dispersion and transformation. Factors such as temperature, humidity, wind speed and direction, and atmospheric pressure can affect pollution levels.
Visibility Data:
- In some areas, reduced visibility due to smog or haze can be an additional measure of air pollution.
Why has the Pollution Increased?
Since the beginning of the industrial revolution in the 19th century, environmental pollution has evolved into a global transboundary issue affecting air, water, soil, and ecosystems. However, It is directly related to human health and well-being. Additionally, Pollution is caused by three major human activities: the use of fossil fuels, particularly by industry and transportation; the use of synthetic fertilisers and pesticides in agriculture; and the increasing use and complexity of chemicals.
In addition to this, Industrialization, the use of pesticides and nitrogen-based fertilisers, crop residues in agriculture, urbanisation, forest fires, desert dust, and insufficient waste management have all contributed to increased environmental health concerns and pollution, particularly in low- and middle-income nations. Moreover, intensive material use depletes natural resources and harms the environment at all stages of the product life cycle, including manufacturing, use, and disposal. By 2050, global garbage is anticipated to reach 3.4 billion tonnes.
Figure -1 Historical and projected trends in ozone concentrations for Europe, North America, and East and South Asia, 1950–2050. (O Wild et al., 2012)
Note: The graphs show the results from a study (research article) that estimates regionally averaged changes in surface ozone due to past or future changes in anthropogenic precursor emissions based on 14 global chemistry transport models. Changes refer to ground-level ozone concentrations 2000, expressed as parts per billion by volume (ppbv).
Conclusion:
In conclusion, while these cities top the charts for their alarming pollution levels, it’s essential to note that air pollution is a global problem. Moreover, air quality and climate change are interrelated issues requiring collaborative solutions. Improving air quality can help with climate change mitigation efforts, and addressing climate change can also help with air quality. This list serves as a wake-up call for governments, industries, and communities to prioritise sustainable practices, invest in cleaner technologies, and raise awareness about health. However, if we practise or adopt sustainability towards a cleaner future, we will achieve SDG -3, 11, 13, 15 for the urban environment.