Air Pollution – An Introduction

The TL;DR:

  • Air pollution contributes to short- and long-term morbidity and mortality from cardiopulmonary causes
  • 4.2 million premature deaths have been attributed to air pollution in 2016 alone
  • Most of the world’s population lives in areas that do not meet the WHO air quality guidelines
  • Children are particularly at risk
  • Low- and middle-income countries are worst affected, although we do not have complete data
  • A multi-faceted approach where industries work together is needed to combat the rise of this problem

This turned out to be too long for a single article (no matter how many cups of tea you have on hand). As such, we’ll be spreading it over the course of a few weeks.

“Air pollution” is one of those terms that has been part of the public consciousness for a long time. So long, in fact, that any kind of specific meaning to the phrase has slowly, imperceptibly, drained away. It has been interwoven with the broader narrative around all kinds of human emissions; often, we think of a miasma overhanging our cities, made of smoke, light, noise and heat. It has such a broad scope that it can easily feel like there are no tangible handholds to grab onto and cause change.

Actually, speaking as a person who has never studied air pollution specifically and therefore has had her information from the media, to me it’s become a kind of grey background noise; a familiar phrase, a colourless warning that never comes to fruition. A problem for the future.

But the headlines are changing.

We have a growing body of information that shows objective links between air pollution and poor health. The numbers are shocking.

  • “7 million deaths every year” are now thought to be due to air pollution [2]
  • “Air pollution cuts two years off global average lifespan” [3]
  • “Diesel pollution stunts children’s lung growth” [4]
  • “Air pollution is the new tobacco” – Dr Tedros Adhanom Ghebreyesus, Director-General of the WHO [5]
  • “Storing up a public health time bomb” [6]

And on 30th October 2018, the World Health Organisation held its first ever Global Conference addressing health and air pollution. [7]

These posts are aimed at people like me – people who don’t know much but want to. It gives a little more information than the media headlines, but no extra statistical analysis or policy discussion. This is a nuts and bolts of what’s happening, and why you should be concerned (but not panicking).

First, we have to understand the problem.

How can we define air pollution?

When we talk about air pollutants, we refer to undesirable atmospheric aerosol particles. Atmospheric aerosol particles are solid or liquid particles which are suspended in the air or atmosphere. Unsurprisingly, some of these will have natural sources; they range from the salt spray over our oceans, to naturally occurring soot and dust.

Air pollutants, then, are those particulates which we have proven to have adverse effects.  Most research will focus on PMs (“particulate matter”) and ozone, because we have been able to show a quantitative relationship between their concentrations in ambient air and health outcomes (more on those below) [8]. PMs, also known as “fine particulates”, are further classified according to their diameter: PM10 particles have a diameter of 10 micrometres or less, while PM2.5s have a diameter of 2.5 micrometres or less – for reference, that’s much less than the diameter of a human hair. PM2.5s include sulfates, nitrates and black carbon.

Broadly, these particles are created when fossil fuels combust. Secondary particles may form, as in the oxidation of sulfur to sulfuric acid. In the presence of ammonia, ammonium salts may form. All of these secondary products may further contribute to poor health outcomes.

We think of air pollution as the ominous tower of thick, oily grey, looming over a power station’s tower. The reality is that most of these particles are invisible, and concentrate most highly where they are produced.

We can think of the sources of fine particulates as split between natural and manmade: in nature, we see them created from volcanoes, dust storms and fires. Of course, these can be expected to become more significant and frequent with the worsening of climate change. Anthropogenically, we create fine particulates by the burning of fossil fuels or large swathes of vegetation; power plants, wet cooling towers, industrial processes, farming, transport, and where burning coal or other matter may be the primary source of heat in the home (more on that later).

Alternatively, and more usefully for research and management of the issue, the WHO tends to classify air pollutants as “ambient” (3.7 million deaths annually [9]) and “household” (4.3 million deaths annually [9]). Although the direct burning of fossil fuels, coal or dung inside the home is estimated to affect around 3 billion people [10], the WHO’s database on the technologies and fuels used for major household energy [11] is incomplete, so we may be underestimating the scale of that issue.

In low- and middle-income countries we know that there are many households who still cook using fuels such as wood, crop waste, charcoal, coal, dung and kerosene, typically in open fires or less-than-modern stoves (paraphrased from [12]). These fires expose nearby people to higher levels of damaging fine particulates. In some houses, with poor ventilation, indoor smoke can reach levels 100 times higher than what is considered acceptable. Further, if the culture results in women and children spending more time around the home hearth, they are put at greater risk via longer exposure. [12]

Let’s talk about that.

Editor’s Note: Join us next week as we look into what health impacts air pollution can have and the scale of the problem.

Author Details: Dr. Katherine Smith, Foundation Year 2

[1] World Health Organisation, “Ambient (outdoor) air quality and health,” 2018.
[2] World Health Organisation, “9 out of 10 people worldwide breathe polluted air, but more countries are taking action,” 2 May 2018. [Online]. Available: [Accessed 4 November 2018].
[3] The Guardian, “Air pollution cuts two years off global average lifespan, says study,” 20 November 2018. [Online]. Available:
[4] The Guardian, “Diesel pollution stunts children’s lung growth, major study shows,” 14 November 2018. [Online]. Available:
[5] The Guardian, “Air pollution is the ‘new tobacco’, warns WHO head,” The Guardian, 27 October 2018. [Online]. Available: [Accessed 4 November 2018].
[6] The Guardian, “90% of world’s children are breathing toxic air, WHO study finds,” 29 October 2018. [Online]. Available: [Accessed 4 November 2018].
[7] World Health Organisation, “First WHO Global Conference on Air Pollution and Health, 30 October – 1 November 2018,” 2018. [Online]. Available: [Accessed 4 November 2018].
[8] World Health Organisation, “WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide; Global update 2005; summary of risk assessment,” World Health Organisation, 2005.
[9] World Health Organisation, “Sixty-ninth World Health Assembly update,” 27 May 2016. [Online]. Available: [Accessed 4 November 2018].
[10] World Health Organisation, “The Cost of a Polluted Environment,” 6 March 2017. [Online]. Available: [Accessed 30 October 2018].
[11] World Health Organisation, “Household Energy Database,” [Online]. Available:
[12] World Health Organisation, “Household air pollution and health,” 8 May 2018. [Online]. Available: Exposure to household air pollution almost doubles the risk for childhood pneumonia and is responsible for 45% of all pneumonia deaths in children less than 5 years old. . [Accessed 15 December 2018].

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