How do fine particulates affect health?
The most widely proposed theory runs thus: when inhaled, fine particulates are so small that they can penetrate deep into the lungs, and settle in the tissue or even cross into the bloodstream. They cause inflammation locally, which exacerbates and accelerates any predisposition to lung disease; and systemically, causing a systemic inflammatory response with activation of pro-inflammatory mediators, white blood cells and platelets, which causes endothelial activation and destabilises atherosclerotic plaques. Ultimately, we can see our way to cardiopulmonary morbidity. 
The evidence backs this up. Exposure to fine particulates and sulphur oxide specifically has been linked to mortality, especially via the heart and lungs: “Each 10-microg/m(3) elevation in fine particulate air pollution was associated with approximately a 4%, 6%, and 8% increased risk of all-cause, cardiopulmonary, and lung cancer mortality, respectively.”  By these, it particularly refers to chronic obstructive pulmonary disease, heart disease, stroke, and lung cancer. This relationship is borne out again and again. It’s worth noting that studies do not see an association with bigger particles; it’s specifically the fine ones. In fact, we now class airborne fine particulates as a Class 1 Carcinogen .
It isn’t just mortality, either; study after study has seen an association with respiratory morbidity, especially asthma attacks, pneumonia, and more broadly, hospital admissions for respiratory or cardiovascular events, including heart attacks. We can think about risk in the long- and short-term; long-term exposure to PMs increases risks of mortality and morbidity, yes, but even short-term high-level exposure, such as due to a fire or dust storm, can increase numbers of hospital admissions due to exacerbations of chronic cardiopulmonary diseases [4-8].
It’s also interesting to note that there is no level at which we do not see it causing disease; no minimum “safe level” . So for my money, all efforts should be made to minimise levels as far as we can, not just to a pre-determined “better” target.
So air pollution is causing morbidity and mortality, but just how bad can the problem be. Well here are some big picture statistics courtesy of the WHO:
- “7 million people die every year from exposure to fine particles in polluted air.” 
- 24% of all adult deaths from heart disease, 25% from stroke, 43% from chronic obstructive pulmonary disease and 29% from lung cancer. 
- 9 out of 10 people worldwide “breathe air containing high levels of pollutants” as defined by the WHO 
- Ambient air pollution may cause 3.7 million deaths annually 
- Household air pollution may cause 4.3 million deaths annually 
- In Europe in 2015, PM2.5 concentrations “were responsible for about 422,000 premature deaths originating from long-term exposure” 
So who is most at risk? Turns out, air pollution does not really impact on everyone equally. We’ve alluded to this in part in our articles so far but tune in next week to find out exactly who might be in the most trouble!
Author Details: Dr. Katherine Smith, Foundation Year 2
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 P. C. Arden Pope III, P. Richard T. Burnett and M. Michael J. Thun, “Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution,” Journal of the American Medical Association, vol. 9, no. 287, pp. 1132-41, 2002.
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 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.
 World Health Organisation, “9 out of 10 people worldwide breathe polluted air, but more countries are taking action,” 2 May 2018. [Online]. Available: https://www.who.int/news-room/detail/02-05-2018-9-out-of-10-people-worldwide-breathe-polluted-air-but-more-countries-are-taking-action. [Accessed 4 November 2018].
 World Health Organisation, “Sixty-ninth World Health Assembly update,” 27 May 2016. [Online]. Available: http://www.who.int/news-room/detail/27-05-2016-sixty-ninth-world-health-assembly-update. [Accessed 4 November 2018].
 European Environment Agency, “EEA Report No 12/2018,” 29 October 2018. [Online]. Available: https://www.eea.europa.eu/publications/air-quality-in-europe-2018. [Accessed 15 December 2018].