Air Pollution: Cities With The Dirtiest Air Globally

Air pollution is a significant global health problem, causing over 10% of worldwide deaths, according to The Lancet. The World Health Organization (WHO) has set a target of 0-10 µg/m³ for air pollution, but 91-99% of the world's population lives in areas where air quality falls short of this guideline. Several organizations, including IQ Air and the Health Effects Institute, have compiled lists of the most polluted countries and cities worldwide. Various factors contribute to poor air quality, such as desert dust, vehicle emissions, and biomass burning. While some countries, like Bangladesh, have shown slight improvements, others, such as Chad, have seen a concerning rise in pollution levels, making it the world's most polluted country in 2022.

The World Health Organization's guidelines

The guidelines provide recommendations on air quality levels and interim targets for several key air pollutants, including particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO). These pollutants have been associated with significant health risks, including cardiovascular and respiratory diseases, and even certain types of cancer. According to the WHO, almost 80% of deaths related to PM₂.₅ could be avoided if current air pollution levels were reduced to those proposed in the updated guidelines.

The guidelines are designed to be a practical tool for improving air quality and reducing suffering and saving lives, especially in low- and middle-income countries, which are disproportionately affected by air pollution due to large-scale urbanization and economic development that relies heavily on the burning of fossil fuels. While the guidelines are not legally binding, they serve as an essential reference for policymakers to guide legislation and policies aimed at reducing air pollution levels.

The WHO also provides qualitative statements on good practices for the management of certain types of particulate matter, such as black carbon, ultrafine particles, and particles originating from sand and dust storms. These statements are based on extensive scientific evidence and identify the levels of air quality necessary to protect public health worldwide. The guidelines are an important tool for protecting public health and reducing the burden of disease associated with air pollution exposure, which is estimated to cause millions of premature deaths and result in the loss of millions of healthy years of life annually.

Air pollution health risks

Air pollution is the presence of contaminants in the atmosphere, such as dust, fumes, gases, and smoke, which can be harmful to human health. It is among the biggest health problems of modern industrial society and is responsible for a significant number of deaths worldwide. Almost every organ in the body can be impacted by air pollution.

One of the main pathways of exposure to air pollution is through the respiratory tract. Pollutants such as fine particulate matter can penetrate deep into the lungs, enter the bloodstream, and travel to other 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 developing non-communicable diseases, such as stroke, heart disease, chronic obstructive pulmonary disease (COPD), and cancer. Children who grow up in high-pollution areas are more likely to develop asthma and bronchitis symptoms in adulthood.

Air pollution has also been linked to adverse pregnancy outcomes, including low birth weight, premature birth, and an increased risk of pre-term birth. Exposure to pollutants during pregnancy may also impact neurological development in children, increasing the risk of cognitive and emotional problems later in adolescence. Fine particulate matter can impair blood vessel function and speed up the calcification of arteries, increasing the risk of cardiovascular problems.

In addition, air pollution is associated with oxidative stress and inflammation in human cells, which can lay the foundation for chronic diseases and cancer. Research has found links between air pollution and increased risks of various cancers, including breast cancer, lung cancer, colorectal cancer, and prostate cancer. Exposure to indoor air pollution, such as from household fuels and technologies, also poses significant health risks.

It is important to note that the health risks associated with air pollution are not evenly distributed. Certain populations are more vulnerable to the harmful effects of air pollution, including children, the elderly, pregnant women, and individuals with pre-existing chronic conditions. Additionally, socio-economic factors play a role, with people of color, low-income communities, and those facing psychosocial stress being disproportionately impacted by air pollution.

Chad: the most polluted country in 2022

Chad was the world's most polluted country in 2022, with a PM2.5 concentration of 89.7, a notable increase from 75.9 in 2021. The air quality crisis in Chad is driven by factors such as desert dust, vehicle emissions, and biomass burning. Chad's capital, N'Djamena, is frequently affected by dust storms, which blanket the city. The country's growing reliance on biomass as the primary energy source for cooking and heating has significantly increased indoor pollution, posing dire health risks to its population, particularly vulnerable groups such as children and women.

The World Health Organization's (WHO) target for air pollution is 0-10 µg/m³, and only seven countries met this guideline in 2025. IQ Air, which measures pollution in 109 countries, considers measurements above 35.5 to be unhealthy for sensitive groups, levels between 55.5 and 150.4 to be unhealthy for all, and anything higher is classified as very unhealthy or hazardous. Chad's PM2.5 concentration far exceeds the recommended limit, indicating a severe air quality issue.

The air pollution crisis in Chad is influenced by several factors. Firstly, the country's geographical location makes it susceptible to desert dust and dust storms, which naturally increase the level of particulate matter in the air. Additionally, vehicle emissions contribute significantly to the problem, especially in urban areas. The increase in traffic congestion leads to higher levels of harmful pollutants being released into the atmosphere. Moreover, Chad's reliance on biomass as an energy source for cooking and heating has dire indoor pollution consequences, further exacerbating the overall pollution levels in the country.

While Chad ranked as the most polluted country in 2022, other countries have also faced significant air quality challenges. For instance, Iraq's pollution levels have sharply increased, with a PM2.5 concentration of 80.1 in 2022. This rise is attributed to industrial growth, traffic congestion, and dust storms. Bahrain has also experienced fluctuations in its PM2.5 concentrations, with values ranging from 39.7 in 2020 to 66.6 in 2022, influenced by industrial emissions and heavy traffic. Pakistan's air quality has seen a similar pattern, with a PM2.5 concentration of 70.9 in 2022, reflecting the ongoing struggle against vehicle emissions, industrial discharges, and agricultural burning.

The consequences of air pollution in Chad and other affected countries are severe. According to The Lancet, air pollution is responsible for more than 10% of all deaths worldwide, amounting to nearly 4.5 million premature deaths in 2019. It negatively affects almost every organ and system in the human body and has detrimental effects on nature as well. The increasing indoor pollution levels in Chad, especially from biomass burning, pose urgent health risks, particularly to vulnerable populations. Therefore, addressing the air quality crisis in Chad and other highly polluted countries is essential to safeguard the health and well-being of their citizens and mitigate the environmental impact.

Bangladesh's air quality improvement

Bangladesh is one of the most polluted countries in the world. Its dense population of over 160 million people, economic growth, and proximity to other polluted countries like India, China, Myanmar, and Nepal contribute to its poor air quality. The main sources of air pollution in Bangladesh are vehicular emissions, fumes from factories and brick kilns, dust accumulation, and waste burning. These emissions release pollutants such as carbon monoxide, ozone, nitrogen dioxide, sulfur dioxide, black carbon, furans, dioxins, lead, mercury, and more. The health consequences are dire, with air pollution causing more than 159,000 premature deaths annually and adding to the infant mortality rate.

To improve Bangladesh's air quality, a collaborative effort is required from all sectors of society, including the government, private sector, and citizens. Here are some key strategies that can be implemented:

• Enforce emission limits and promote cleaner fuels and technologies: Bangladesh should enforce emission limits for vehicles, factories, and power plants, encouraging the use of cleaner fuels and energy-efficient technologies. This includes promoting the use of cleaner cooking fuels and stoves, as solid fuels and traditional cookstoves currently contribute significantly to indoor air pollution.
• Improve waste management practices: Open burning of municipal solid waste, especially in Dhaka, contributes to air pollution. Implementing better waste management practices and regulations can help reduce this source of pollution.
• Address dust accumulation: While often overlooked, dust accumulation, particularly from construction and industrial activities, is a significant contributor to PM2.5 and PM10 levels. Measures such as regular street cleaning, dust control on construction sites, and the use of dust masks can help mitigate this issue.
• Enhance data accessibility and transparency: Bangladesh can improve the availability and accessibility of timely air quality data. Making this data open to the public will enable citizens, researchers, and innovators to actively participate in addressing air pollution through the development of solutions and policies.
• Regional cooperation: Bangladesh shares an airshed with India, Nepal, and Pakistan, where particulate matter moves freely across borders. Regional cooperation and dialogue are crucial to effectively tackle air pollution, as individual efforts may be hindered by emissions from neighboring countries.
• Incentivize the private sector: The private sector has a crucial role in adopting cleaner production systems and technologies. Incentives and support can encourage industries to transition to more sustainable practices, recognizing the long-term economic benefits of green growth and the creation of green jobs.
• Promote preventative measures for citizens: Citizens can take preventative measures to protect themselves from the harmful effects of air pollution, such as wearing high-quality air filtering masks and staying informed about pollution levels through apps and websites.

By implementing these strategies and working collectively, Bangladesh can significantly improve its air quality, reduce health risks, and create a more sustainable future for its citizens.

Air pollution sources and factors

Air pollution is a pressing issue that poses significant risks to human health and the planet. It is caused by various sources and factors, which contribute to the contamination of the indoor and outdoor environment. The major sources of air pollution can be categorised into four groups: mobile sources, stationary sources, area sources, and natural sources.

Mobile sources, such as cars, buses, planes, trucks, and trains, are a primary contributor to air pollution. These vehicles emit pollutants like nitrogen dioxide and particulate matter, which can have detrimental effects on human health and the environment. In the United States, mobile sources account for more than half of the country's air pollution, with automobiles being the main culprit.

Stationary sources, on the other hand, include power plants, oil refineries, industrial facilities, and factories. These sources emit large amounts of pollution from a single location and are also known as point sources. They release pollutants such as sulfur dioxide, nitrogen oxides, and volatile organic compounds, which can have long-lasting impacts on air quality and human health.

Area sources encompass agricultural areas, cities, and wood-burning fireplaces. While individual sources within this category may not have a significant impact, collectively, they can contribute substantially to air pollution. Residential energy use for cooking and heating, waste incineration, and industrial processes in urban areas can lead to elevated levels of pollutants in the air.

Lastly, natural sources, such as wind-blown dust, wildfires, and volcanic activity, can also contribute to air pollution. While these sources may not consistently cause ongoing pollution problems, they can have significant impacts, especially when combined with human-generated pollution. For example, parks located downwind of power plants may experience increased smog due to the interaction of natural wind patterns and emissions from stationary sources.

It is important to note that the effects of air pollution vary depending on factors such as the type of pollutant, the duration and level of exposure, individual health risks, and the cumulative impacts of multiple pollutants. Addressing air pollution requires a multifaceted approach, including policy interventions, sustainable practices, and public awareness, to mitigate the risks associated with these sources and factors.

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