Air pollution: a multifaceted reality
The WHO defines air pollution as "contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere". We can distinguish between two categories of atmospheric pollutants:
- primary pollutants, arising directly from sources of pollution: nitrogen monoxide, sulphur dioxide, carbon monoxide, fine particles or dust in suspension (PM2.5 and PM10), heavy metals, volatile organic compounds, hydrocarbons etc.
- secondary pollutants arising from chemical reactions between gases: ozone, nitrogen dioxide etc.
As an adult breathes in 15,000 litres of air a day on average, the presence of these pollutants in the air can contribute to the development or worsening of cardiovascular diseases, chronic lung diseases, respiratory infections etc. Thus, according to the WHO, exposure to indoor and outdoor air pollution leads to about seven million premature deaths worldwide every year, making it the fourth biggest factor in premature death at a global level.
Air pollution also has an impact on ecosystems, contributing to phenomena such as acid rain and eutrophication.
Sources of air pollution
Though several natural phenomena contribute to air pollution (volcanic eruptions, soil erosion etc.), many atmospheric pollutants are of human origin:
· heating, electricity generation and car and ship engines involve combustion phenomena that can cause emissions of nitrogen dioxide;
· the use of solvents and paints for domestic or industrial purposes is one of the main sources of volatile organic compound emissions;
· sulphur dioxide is produced by burning fossil fuels (domestic heating, energy generation, internal combustion engines etc.);
· while ozone results from the transformation of primary pollutants. This transformation occurs under the effect of UV radiation from the sun and is encouraged by high temperatures.
In that respect, the fight against air pollution is aligned with the fight against climate change, for the two phenomena, though separate, are linked. Just as global warming contributes to worsening air pollution, some pollutants, such as black carbon particles and ozone, are themselves factors in global warming.
All equally affected by air pollution?
91% of the world's population live in areas where air pollution exceeds the thresholds set by the WHO, which are an average of 20 µg/m3 a year for large particles (PM10) and 10 µg/m3 a year for fine particles (PM2.5). Figures up to five times higher than these values are observed in a many large cities worldwide. These alarming results show the global scale of the phenomenon.
While air pollution is a global problem, its effects fall most heavily on vulnerable people (pregnant women, babies and young children, elderly people etc.) and developing countries. The World Bank indeed estimates that 93% of deaths and non-fatal diseases attributed to air pollution worldwide occur in these countries
Time to act in response to the emergency
Faced with these worrying indicators, many measures have been introduced across the world and improvements can already be seen.
In high-income countries, a reduction in air pollution has been detected in nearly half of cities that introduced monitoring between 2008 and 2013. A 5% drop has also been seen in low and medium-income countries over the same period. This spectacular progress can be explained by the implementation of proactive public policies supported by the emergence of new technological solutions provided by companies such as SUEZ, some of which will be described in this series on air quality.
In the world's big cities, air quality is now a key aspect of attractiveness and public health. With initiatives such as increasing green spaces, building eco-districts, bioclimatic architecture and sustainable transport provision, cities are innovating, uniting their actions and sharing their best practice, as demonstrated by the Air Quality Network launched in 2018 by the C40 group. Initiatives are multiplying across the globe. In China, the city of Shenzhen has become the first city in the world with a fully electric bus fleet. In India, cities are at the heart of the National Clean Air Programme, launched by the government in January 2019 with the goal of reducing particle emissions by 20 to 30% by 2024. Meanwhile, Paris has just launched a pilot project with Bloomberg Philanthropies to measure pollutants at the city's schools and crèches.
At the heart of these initiatives, the data collected is more and more precise thanks to the development of new technologies. Smart sensors, artificial intelligence, modelling tools, mobile apps... all these innovations enable better understanding, analysis and anticipation of pollutant emissions in the atmosphere. Supporting decision making, this information is invaluable in making everyone – public authorities, businesses and citizens, each at their own level – active players in the fight against this global scourge.