Air Pollution: Where Is It Worst?

Air pollution is a significant health and environmental problem worldwide, causing over 7 million premature deaths annually. It is a silent killer, as it is rarely the direct cause of death, but rather a contributing factor. Air pollution is caused by both natural and manmade sources, with the latter being the leading contributor in cities. The impact of air pollution varies across the world, with low- and middle-income countries suffering the highest exposures. According to the World Health Organization (WHO), 99% of the global population breathes air that exceeds their guideline limits, with Central and South Asia among the top ten most polluted cities in the world.

Indoor air pollution

Air pollution is a significant global health problem, and while outdoor air pollution may be more noticeable, indoor air pollution is also a pressing issue. Indoor Air Quality (IAQ) refers to the air quality within and around buildings and structures, especially in relation to the health and comfort of those inside.

Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality issues. Inadequate ventilation can increase indoor pollution levels by not diluting emissions and carrying pollutants out of the indoor space. High temperatures and humidity can also increase indoor pollutant concentrations. Common sources of indoor air pollution include building materials, household cleaners, and biological pollutants like dust mites and pet dander. In poorly ventilated homes that use polluting fuels for cooking and heating, indoor smoke can reach levels 100 times higher than acceptable. The use of open fires or inefficient stoves fuelled by kerosene, biomass (wood, animal dung, crop waste), and coal is prevalent among around 2.1 billion people worldwide. This generates harmful household air pollution, which was responsible for an estimated 3.2 million deaths per year in 2020, including over 237,000 children under five.

The World Health Organization (WHO) has issued guidelines for indoor air quality and household fuel combustion to address this issue. These guidelines offer practical, evidence-based advice on the types of fuels and technologies that can be considered clean and protect health. For example, solar, electricity, biogas, liquefied petroleum gas (LPG), natural gas, alcohol fuels, and certain biomass stoves are recommended. Additionally, the guidelines emphasize addressing all household energy uses, especially cooking, space heating, and lighting, to benefit health and the environment.

The effects of indoor air pollution on health can be both immediate and long-term. Immediate effects include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. These are usually short-term and treatable, and removing the person from the source of pollution can alleviate symptoms. However, repeated exposures to indoor pollutants can lead to the development or worsening of diseases like asthma and other respiratory illnesses. Long-term effects of indoor air pollution include respiratory diseases, heart disease, and cancer, which can be severely debilitating or fatal.

While outdoor air pollution may be more visible, indoor air pollution is a significant health hazard that affects a large portion of the global population. The use of polluting fuels and inefficient technologies in households, particularly in developing countries, contributes to high levels of indoor air pollution, leading to serious health issues and premature deaths. Addressing indoor air quality through improved ventilation, cleaner fuels, and technology adoption is crucial to mitigate these negative impacts.

Outdoor air pollution

The burden of outdoor air pollution is disproportionately borne by individuals in low- and middle-income countries, where 89% of premature deaths occur. The greatest burden is found in the WHO South-East Asia and Western Pacific Regions. As countries industrialize and transition from low to middle incomes, outdoor air pollution tends to worsen. This is due to increased emissions from various forms of combustion, such as gas-powered transportation (cars, planes, and trains) and industrial activities.

While natural sources, such as windblown dust, volcanic smoke, and burning materials, contribute to outdoor air pollution, human activities are the leading cause of pollution in cities. Fine dust particles (PM2.5) up to 2.5 micrometers in diameter, produced primarily by human activities, can penetrate deep into the lungs and enter the bloodstream, causing significant health risks. These include short-term effects like difficulty breathing, chest pain, and irritation of the eyes, nose, and throat, as well as long-term effects like lung tissue damage, cancer, early death, and the development of respiratory illnesses.

Addressing outdoor air pollution requires concerted action from policymakers in sectors like energy, transport, waste management, urban planning, and agriculture. Implementing policies and investments that support cleaner transportation, energy-efficient homes, improved power generation, and better waste management can effectively reduce key sources of outdoor air pollution. Additionally, individuals can take measures such as wearing N95 masks and using air purifiers to mitigate their exposure to polluted air.

Natural sources

Air pollution is a significant environmental health hazard and a leading cause of early death worldwide. While human activities, such as industrial processes and transportation, are major contributors to air pollution, natural sources also play a role in degrading air quality. These natural sources of air pollution include:

• Wildfires: Wildfires release smoke and particulate matter into the air, which can spread over large areas, affecting both local and downwind regions. Forested areas are particularly susceptible to the effects of wildfires on air quality.
• Volcanic Activity: Volcanic eruptions release smoke, ash, and gases into the atmosphere, which can have significant impacts on air quality. The effects of volcanic activity can be felt both locally and at a distance, depending on wind patterns.
• Dust and Sandstorms: Windblown dust and sand, particularly from large deserts like the Sahara, can be carried over long distances, affecting air quality in various regions. These particles can cause respiratory issues and other health problems.
• Agricultural Emissions: While often associated with human activities, agricultural emissions can also have natural components. Certain farming practices, such as the heavy use of fertilizers, contribute to fine-particulate air pollution. This is a significant issue in many parts of the world, including the United States, Europe, Russia, and China.
• Biogenic Volatile Organic Compounds (BVOCs): These are organic compounds emitted by plants and trees. While they play a crucial role in natural processes, such as plant growth and atmospheric chemistry, some BVOCs can have negative effects on air quality. Isoprene, for example, is a common BVOC that can contribute to the formation of ground-level ozone, a harmful pollutant.

It is important to note that while natural sources of air pollution exist, human activities remain the leading cause of air quality degradation, particularly in urban areas. The impact of natural sources can vary based on geographical location and local environmental factors. Additionally, the interaction between natural and anthropogenic (human-caused) pollutants can lead to complex chemical reactions in the atmosphere, further complicating the understanding of air pollution sources.

Manmade sources

Transportation, including fuel combustion in motor vehicles like cars, trucks, trains, planes, and ships, is a significant contributor to elevated levels of fine particulate matter (PM2.5), ozone, and nitrogen dioxide (NO2). The majority of emissions from transportation occur in the world's top vehicle markets, with a strong correlation between per capita transport emissions and incomes.

Industrial businesses, such as power plants, refineries, and factories, also contribute to air pollution through combustion processes. These facilities emit nitrogen oxides (NOx), hydrogen sulfide, volatile organic compounds (VOCs), and particulate matter, which contribute to ozone and smog formation. Industrial activity is a major global source of these pollutants, impacting human health and the environment.

Another manmade source of air pollution is biomass burning, which includes the burning of plant matter or coal for heating, cooking, and energy generation. This practice emits particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), sulfur dioxide (SO2), and other hazardous air pollutants (HAPs). Residential cooking and heating, particularly in households that use solid fuels like coal or wood, contribute significantly to indoor and ambient air pollution.

Agriculture is also a significant manmade source of air pollution, especially with the heavy use of fertilizers on agricultural land. Pollution generated from farms can outweigh other manmade sources of particulate matter in certain regions, including the United States, Europe, Russia, and China. The use of fertilizers and agricultural waste incineration contributes to fine-particulate air pollution.

To mitigate the impact of these manmade sources, interventions such as transitioning to cleaner fuels, improving industrial processes, adopting renewable energy sources, and implementing regulations and policies that promote sustainable land use, cleaner household energy, and efficient transportation are essential.

Global disease burden

Air pollution is a significant global health problem, causing an estimated 3.1 million premature deaths worldwide each year, according to some sources. Other sources estimate the number of premature deaths caused by air pollution to be as high as 7 million annually. It is the fourth leading cause of early death and accounts for 3.2% of the global disease burden.

The World Health Organization (WHO) has found that 99% of the global population breathes air that exceeds its guideline limits and contains high levels of pollutants. This figure is supported by other sources. Low- and middle-income countries suffer the highest exposures, with the largest burden of disease related to air pollution found in the Western Pacific and South-East Asia, due to heavy industry and air pollution hotspots in developing nations. In 2012, low and middle-income countries in the WHO's South-East Asia and Western Pacific regions accounted for 7.1 million deaths related to air pollution.

Air pollution has been linked to a range of diseases, including respiratory diseases like pneumonia, cardiovascular disease, ischemic heart disease, stroke, lung cancer, chronic respiratory diseases such as COPD, diabetes, and lower birth weight and premature births. According to the Global Burden of Disease study, household air pollution and ambient particulate matter pollution are among the top risk factors for loss of healthy life years.

Particulate matter air pollution caused 8% of the total disease burden in 2021, making it the leading contributor among risk factors. It is responsible for 48% of chronic obstructive pulmonary disease (COPD) cases and 34% of preterm births in 2021 were attributed to exposure to air pollution. Overall, 33% of deaths due to air pollution occurred in South Asia in 2021.

Transport emissions are a major contributor to elevated levels of fine particulate matter, with the majority of emissions occurring in the world's top vehicle markets. Natural sources of air pollution include volcanic activity, wildfires, and dust or sandstorms. However, man-made sources tend to be the leading contributors to air pollution in cities and are more easily influenced by regulations.

Frequently asked questions