Air Pollution: What Does It Look Like?

Air pollution is a global health and environmental issue that affects people in all countries. It is caused by both natural and human-made sources, with the latter being the leading contributor, especially in cities. Human-made sources include the burning of fossil fuels, such as coal, natural gas, and oil, as well as industrial emissions, vehicle emissions, and agricultural practices. Natural sources include wildfires, volcanic activity, and windblown dust. Air pollution can manifest as smog, a combination of smoke and fog, which obscures shapes and colours in the environment. It can also directly contaminate water bodies and soil, damaging crops and plants and even buildings. Air pollution has been linked to various diseases, including asthma, heart attacks, stroke, pneumonia, and cancer, making it a significant public health concern worldwide.

Smog, a smoky fog that reduces visibility

Smog, a mixture of smoke and fog, is a significant issue in many cities worldwide, causing reduced visibility and adverse health effects. The term "smog" was first used in the early 1900s to describe the dense mixture of smoke and fog that reduced visibility and posed health risks. Urban smogs, reported as early as the 16th century, caused extreme loss of visibility, often down to just a few meters. These smogs were worsened by ammonia from sources like urban livestock and fertiliser factories, leading to the formation of ammonium sulphate aerosol and encouraging fog formation.

Photochemical smog, a common form of air pollution in modern cities, is produced when sunlight reacts with nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere. Nitrogen oxides originate from car exhaust, coal power plants, and factory emissions, while VOCs are released from gasoline, paints, and cleaning solvents. When exposed to sunlight, these chemicals react to form airborne particles and ground-level ozone, creating smog.

Ground-level ozone is harmful to human health, and smog is often associated with severe health consequences. The Great Smog of 1952 in London, caused by coal pollution, resulted in over 4,000 deaths from respiratory ailments. Additionally, the thick smog led to road, railway, and airport closures, impacting transportation and daily life.

Today, cities like Los Angeles, Delhi, and Beijing are known for their high levels of atmospheric pollution and smog. Inversion traps, which hold pollution close to the ground, contribute to the severity of smog in these cities. The developing smog is often toxic and has been linked to severe sickness, reduced life expectancy, and premature deaths.

While some cities have improved their air quality through local policies and regulations, many continue to struggle with high levels of smog and air pollution. It is essential to address this issue to protect public health and the environment. Strategies such as reducing vehicle emissions, implementing factory restrictions, and encouraging the use of public transportation can help mitigate smog and improve visibility in affected areas.

Haze, caused by pollutants, that makes it hard to see

Haze is an atmospheric phenomenon that occurs when dust, smoke, and other dry particulates become suspended in the air, obscuring visibility and the clarity of the sky. It is often the result of human activities such as industrial emissions, vehicle emissions, and biomass burning, though natural sources like wildfires, volcanic activity, and windblown dust can also contribute.

Haze, particularly in urban areas, is a significant issue as it is detrimental to human health and the environment. The particles that comprise haze, such as PM2.5, NO2, and sulfur dioxide, can be inhaled and impact respiratory health. These particles are very small, measuring 2.5 micrometers in diameter or less, allowing them to be absorbed into the bloodstream upon inhalation. This can lead to increased respiratory illness, decreased lung function, and other systemic effects.

In some cases, haze can be severe enough to cause a reduction in irradiance, affecting photovoltaic production and agricultural yield. It can also impact terrestrial photography and imaging, as the dense atmosphere can result in a loss of contrast and obscure the view of distant subjects. Additionally, haze can migrate to adjacent countries, becoming an international issue.

To address the problems caused by haze, various programs and regulations have been implemented. For example, the Interagency Monitoring of Protected Visual Environments (IMPROVE) program in the United States aims to establish the chemical composition of haze and implement air pollution control measures to restore visibility to pre-industrial levels. Local policies and interventions in cities have also helped improve air quality in some regions.

Exhaust from vehicles, a major source of air pollution

Air pollution is a combination of outdoor and indoor particulate matter and ozone. It is a significant health and environmental problem, contributing to many of the leading causes of death, including heart disease, stroke, lower respiratory infections, lung cancer, diabetes, and chronic obstructive pulmonary disease (COPD). While there are many forms of air pollution, vehicle exhaust emissions are a major source of this issue, particularly in urban areas.

The vast number of petrol and diesel vehicles on the roads, estimated at over 1.45 billion globally, has had a widespread impact on the environment. These vehicles are a significant contributor to air pollution in towns and cities and global greenhouse gas emissions. Older diesel vehicles, in particular, have been targeted for their harmful particulate emissions, and drivers of ageing diesels are being discouraged from entering certain areas through the implementation of low emission zones.

Vehicle exhaust emissions contain a range of harmful substances. One of the most concerning is benzene (C6H6), which occurs naturally in petrol and diesel and is emitted from vehicle exhausts as unburnt fuel. Benzene is a carcinogenic substance, and high levels of inhalation can severely harm human health. In addition to benzene, exhaust fumes also release particulate matter, such as black soot and metal particles, which can be inhaled and have damaging effects on people's health. Modern cars are now fitted with diesel particulate filters (DPFs) to reduce the number of harmful particles emitted, and catalytic converters and particulate filters are standard on all new petrol and diesel cars.

However, it is not just exhaust fumes that contribute to air pollution from vehicles. Brakes and tyres also release tiny fragments of particulate matter, such as dust, into the air, which can have a detrimental impact on human health. Additionally, plastic particles from tyres can harm marine wildlife if they enter water systems. While emissions standards and clean air zones have helped reduce pollution levels in some cities, air quality remains a pressing issue, with many urban residents worldwide still breathing in unhealthy levels of pollution.

Air pollution from wildfires, a growing problem

Air pollution is a pressing health and environmental issue worldwide, contributing to about 7 million premature deaths annually. It is caused by both natural and manmade sources, with the latter being the predominant factor in cities. Human activities such as burning fossil fuels, transportation, and industrial processes release greenhouse gases and black carbon emissions, which fuel climate change. As the climate crisis intensifies, wildfires are becoming increasingly prevalent, and with them, a surge in air pollution and its detrimental health effects.

Wildfires are one of the largest sources of black carbon, a super pollutant that exacerbates climate change and extreme wildfires. They release a range of pollutants, including particulate matter (PM), carbon monoxide, nitrogen oxides, and hazardous air pollutants (HAPs). These emissions can spread far and wide, impacting both human health and the environment. The burning of trees and organic material releases fine particles (PM2.5) that, due to their minuscule size, can be easily inhaled into the lungs and even the bloodstream, causing a range of adverse health effects.

The impact of wildfires on air quality was evident in the 2021 summer fire season in North America and Russia. Researchers found elevated levels of PM2.5, exceeding the World Health Organization's recommendations by several times. This is particularly concerning as PM2.5 exposure is linked to aggravated asthma symptoms, the development of asthma in children, and other serious health issues. The Canadian wildfires, for instance, released more carbon in five months than Russia or Japan emitted from fossil fuels throughout 2022.

As the world warms, the number of wildfires is projected to increase significantly. Climate change is making these fires more frequent and intense, creating a vicious cycle. The burning of peatlands, which are large repositories of organic carbon, further exacerbates the problem by releasing greenhouse gases. To break this cycle, a joined-up approach is necessary, addressing the interconnectedness of climate change, air pollution, and wildfires. Preventing wildfires through increased planning and community engagement in forest management is crucial, along with mitigating their impact on air quality and human health.

Health effects, including respiratory and cardiovascular issues

Air pollution is a combination of outdoor and indoor particulate matter and ozone. It is one of the world's largest health and environmental problems, contributing to the global disease burden and causing early deaths.

Fine particle pollution, or PM2.5, is a major concern in urban environments. These particles are 2.5 micrometres or smaller in diameter, allowing them to easily enter the lungs and, in some cases, the bloodstream. This can cause inflammation and oxidative stress, impacting the lungs, heart, and brain, among other organs, and leading to various diseases. Short-term exposure to high levels of particulate matter can cause reduced lung function, respiratory infections, and aggravated asthma. Constant exposure to elevated particle pollution will contribute to reduced respiratory function even in healthy people.

Long-term exposure to fine particle pollution increases the risk of diseases with a longer onset, such as non-communicable diseases, including stroke, heart disease, chronic obstructive pulmonary disease (COPD), and lung cancer. Research has also linked year-round exposure to particle pollution to a wide array of serious health effects at every stage of life, from conception to old age. For example, it can increase the likelihood of developing diabetes, cognitive impairment, and neurological diseases, as well as adverse pregnancy outcomes such as low birth weight.

Nitrogen dioxide (NO2) is another significant pollutant in urban areas, primarily from vehicle emissions. Exposure to NO2 is linked to asthma development in children and the aggravation of asthma symptoms. It is also associated with an increased risk of respiratory and cardiovascular disease mortality.

Overall, air pollution is a severe health issue, causing and exacerbating various respiratory and cardiovascular issues. It is a particular concern in cities, where most residents are breathing unhealthy levels of pollution.

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