Introduction

In an increasingly industrialised world, the problem of increasing air pollution has been at the forefront of public health for a long time. This article will discuss the health effects air pollution can have on society.

What is air pollution?

There are two major contributors to the air pollution that currently exist within our atmospheres. The first is particulate matter (PM) which is a mixture of solid and liquid particulates that are suspended in the air, and are a by-product of the burning of fossil fuels, vegetation and livestock production and chemical reactions between organic compounds and nitrogen oxides.¹ The average levels of PM concentration are higher in more urbanised, populated areas.² Data from over 50 countries, found that in cities, traffic contributes to 25% of the total PM concentration, followed by unspecified sources of human origin (22%), domestic fuel burning (20%), natural dust and salt (18%), and industrial activities (15%).³

The other major contributor to air pollution is the depletion of the ozone (O₃) layer, which acts as a shield in the earth’s atmosphere and protects against the harmful effects of ultraviolet (UV) radiation that comes from the sun.⁴ Human activity has contributed to the depletion of the O₃ layer through the production of halocarbons such as chlorofluorocarbons (CFCs), hydro-fluorocarbons (HFCs) and bromofluorocarbons (BFCs), which react with the O₃ layer, causing it to breakdown.⁵In 2010, the Montreal Protocol on substances that deplete the ozone layer banned the global production of CFCs.⁶ However, data indicates that between 2010 and 2020, the atmospheric abundances and emissions of 5 CFCs increased; which is likely because CFCs can still be produced if they are to be used as a feedstock for the production of other chemicals.⁷

What are the health effects of air pollution?

Respiratory health

In 2012, the World Health Organisation (WHO), estimated that exposure to air pollution led to ~7 million deaths each year, or 1 in 8 deaths worldwide.⁸

This puts into context the scale of the problem that air pollution poses to public health. Different forms of air pollution have different health effects on the human population. For PM, perhaps the most obvious way that it can damage health is the respiratory system, with air pollution known to be a risk factor for various respiratory diseases.9 Chronic Obstructive Pulmonary Disorder (COPD) is a respiratory disease characterised by chronic airway obstruction due to inflammation of the lungs, in response to harmful exposures.¹⁰ One such exposure that is associated with the disease is air pollution, with research indicating that short-term exposure to PM is associated with an increased risk of hospitalisation for COPD and asthma.¹¹

Asthma is another respiratory disease that is associated with air pollution, in a similar vein to COPD.¹² Asthma is also an inflammatory disease of the airways, which is characterised by hyperresponsiveness to stimuli and increased mucus secretion.¹³ At high concentrations, airway inflammation and hyperresponsiveness can be induced by air pollutants, aggravating asthma sufferers.⁹

Air pollution is also a risk factor for lung cancer, and while smoking remains the biggest contributor to the development of the disease, exposure to ambient air pollution is associated with increased lung cancer incidence and increased mortality, and exposure shortens survival times following a diagnosis.¹⁴ Furthermore, while it may take a while to fully establish the association between long-term exposure to air pollution and lung cancer, the incidence rate of the disease is expected to increase given the rapid rise in industrialisation, an ageing population and a high smoking prevalence amongst the population.¹⁵

Tuberculosis (TB) is the 10th leading cause of death in the world and in 2019, 10 million people were infected with it.¹⁶ TB prevalence is strongly associated with urban settings, where there is greater exposure to air pollution.¹⁷ Research from China indicates too that short-term exposure to air pollution is associated with increased TB morbidity.¹⁸

Cardiovascular health

Cardiovascular disease (CVD) is responsible for more deaths per year than any other disease, and of these, air pollution is attributable to many as it is recognised as an independent risk for CVD.¹⁹ Furthermore, it has been found that the risk of death due to cardiovascular disease or event increases by approximately 1% for every 10µg/m3 increase in PM concentration^.20 Studies have shown that higher levels of PM are associated with excess morbidity in a number of cardiovascular diseases and events including arrhythmias and sudden cardiac death, cardiac ischaemia, heart failure, myocardial infarctions (MI), peripheral arterial disease and stroke.²¹ The effect of air pollution on cardiac events is so pronounced that it has been found that the risk of MI increases by 48% after a 2-hour-long exposure to PM;_2.5 and the risk of heart attack increases 2.73-fold 1 hour after exposure to air pollution from traffic.^22,23 Similarly to respiratory diseases, long-term exposure to air pollution is thought to increase the risk of CVD, but to what effect remains unclear.²¹

UV radiation

The depletion of the O₃ layer as a result of the production of reactive halocarbons can also lead to ill health effects for the public. This is due to an increased exposure to UV radiation which damages the skin either by increasing the frequency of sunburns and/or by impairing the melanocyte cells.⁴ Melanocyte cells are responsible for either skin pigmentation or hair pigmentation, depending on where they are found, and UV exposure stimulates pigmentation, which is why people tan when they have been in the sun for a prolonged period.²⁴ However, chronic UV exposure can lead to DNA damage of the melanocytes, which can give rise to melanoma, which is a type of skin cancer.²⁵ Malignant melanoma, which describes the condition when the cancer spreads to other parts of the body, is the most common fatal skin cancer, and one of the most common causes of cancer in young adults.²⁶ The risk of developing melanomas as a result of increased exposure to UV radiation is significantly higher in fair-skinned people, particularly those with red or blonde hair, and/or those who sunburn and freckle easily, compared to people with darker complexions.²⁵

Vulnerable populations

As noted previously, those with fair skin are more at risk of developing melanomas from increased UV exposure. Similarly, for other air pollution-related morbidities, there are other populations that are more at risk of adverse outcomes. Age is one such risk factor as it has been found that elderly populations have a higher risk of death and disease, mainly from cardiovascular events and diseases, from exposure to ambient air pollution.²⁷ This is likely given that older age is associated with long-term exposure and a weakened immune response.²⁸

Age is also a risk factor at the opposite end of the spectrum, with children known to be disproportionately affected by air pollution.²⁹ This is because while in development, the respiratory systems of children are particularly vulnerable, thus chronic exposure at a young age can have lasting consequences.³⁰

Summary

Air pollution can manifest itself in different ways, each bringing with it, its own particular risk to health. PM is a mixture of solid and liquid particulates which remain suspended in the air. They are produced from a number of different sources including the burning of fossil fuels such as coal, oil and gas, the production of vegetation and livestock, and the by-product of chemical reactions between nitrous oxides and organic compounds. The levels of PM are often worse in more urbanised, densely populated areas, given the increased levels of human activity. 

PM can damage one's health in two major ways. Firstly, through damage to respiratory systems which WHO estimates contributes to 7 million deaths each year. Such conditions which are linked to air pollution exposure and have an increased morbidity rate as a result include COPD, asthma, lung cancer and TB. PM is also damaging to the cardiovascular system, by increasing the risk of incidence for cardiac events and worsening the survival times of those with CVD. Particularly vulnerable populations to PM exposure include children and the elderly.

Air pollution can also occur through depletion of the O₃ layer, due to the production of a particular set of halocarbons, which react with the protective layer, causing it to break down, which increases the exposure to UV radiation from the sun. This increase in UV is particularly harmful to those of a fair complexion, as the radiation can damage their melanocytes, which increases the risk of developing melanomas.