There is nothing more fundamental to human existence than breathing. Without air, people die in a matter of minutes.
As well as the oxygen that is essential for survival, air contains pollutants of increasingly anthropogenic origin. These contaminants are emitted into outdoor air by combustion, which is essential for generating energy, and by the industrial and agricultural processes that underpin every element of modern life. Contaminants also penetrate buildings, in which they mingle with indoor air pollutants, rendering homes and offices not entirely safe.
Each breath brings with it a new load of pollutants — and the lungs are a barrier to them. Although some contaminants are exhaled, a large proportion of them are deposited on the surface of the respiratory tract. From there, they enter the bloodstream and spread throughout the body.
Nature Outlook: Lung health
The consequences for health are profound. Some of these stem from the toxic nature of the pollutant. And some are due to the mere presence of foreign objects on the surface of the lungs and elsewhere in the body. Other health issues are caused by infectious respiratory particles that contain viruses and bacteria. Exposure to particulate matter smaller than 2.5 micrometres (PM 2.5 ), in particular, is the lead contributor to global disease burden, causing cardiovascular diseases, chronic respiratory conditions, lung cancer, diabetes, lower respiratory infection, leukaemia and Parkinson’s disease1.
The fractional contribution of PM 2.5 to disease burden has increased considerably over the past 30 years, owing to both increased exposure and an ageing population. And as better research tools are used to investigate the effects of air pollution, the clearer it is that these occur even at very low levels — no exposure is inconsequential. This understanding has led to modifications of World Health Organization (WHO) air-quality guidelines2, which now set values for five pollutants much lower than previous versions.
The infamous Great Smog of London in 1952 was a wake-up call. It contributed to the deaths of an estimated 12,000 people, and led to the gradual introduction of outdoor air-quality regulations around the world. Such measures have led to cleaner air. In 2013, for example, China introduced radical measures to improve air quality. These have led to the concentration of PM 2.5 decreasing by as much as two-thirds in provincial Chinese capitals3.
But there is still a long way to go. Around 99% of the world’s population lives in areas in which levels of pollutants exceed those recommended by the WHO2. And climate change brings new threats to air quality in the form of increased frequency of wildfires and dust storms (owing to desertification).
Most regulatory attention has gone towards ensuring cleaner outdoor air. But people in many societies spend almost 90% of their time indoors — and there are almost no regulations to protect people’s lungs and health from indoor air pollution. Moreover, even at the onset of the COVID-19 pandemic, global and national authorities still rejected the scientific foundation that governs the spread of respiratory infections. It took an extraordinary effort by an interdisciplinary group of experts to dismantle old dogmas, warn about the risk of airborne infection transmission and to change the course of the pandemic4. There is still a long way to go before society manages the air that people inhale indoors.
Fortunately, there are solutions to reduce the environmental threats to our lungs. First, authorities must intensify efforts to clean up outdoor air. The key requirement is the transition to clean energy, which will vastly reduce combustion emissions from cities and put the world on a better trajectory for addressing climate change. Second, indoor air-performance standards and improved building design standards will ensure clean indoor air in new and existing buildings. To be effective, however, these standards will need to be tough5.
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