Air pollution may be one of the greatest environmental health risks in the world, according to the WHO. There are programs of study suggesting that air pollution affects many organs in addition to the lungs, and those who suffer most are the most exposed or vulnerable people, so it becomes a cross-cutting issue that affects all of society but emphasizes inequalities.

People spend part of their time outdoors and part indoors, and it is worth asking which air is more polluted. After all, indoors people are exposed to different types of chemical pollutants, which in low concentrations can cause headaches, dizziness, fatigue, nausea and, in the long term, harmful health effects.

One of the key factors causing the deterioration of air quality is the construction of more airtight buildings to improve energy efficiency. This airtightness causes the indoor environment to be less regenerated, because less fresh air enters from outside, and pollutants from internal sources (or those infiltrating from outside) become concentrated.

And it so happens that the same polluted and used indoor air that sickens more than a third of the planet will eventually be expelled into the environment, i.e. the city in the case of urban buildings. So what is the outdoor air pollution generated by a building? What are the pollutants exhaled by the buildings? Are they sufficiently diluted?

And even more: do the ventilation systems of buildings that expel these pollutants outside, into the city, then reintroduce them into the buildings? Are we facing a vicious circle similar to that of plastic waste that is dumped into the ocean and then enters people through the food chain?

For example, one source is the cosmetics used in the bathroom. The levels of volatile organic compounds that are expelled through ventilation follow a dynamic compatible with their daily use guideline . On the other hand, particulate pollution is related to cooking stoves. These two groups of pollutants, to which methane (a potent greenhouse gas) must be added, appear to be the main contributions of buildings to urban air quality.

Other exhaled pollutants have a more dubious origin, less regular over time: for example, carbon monoxide. It could be attributed to tobacco or other combustion, because the main source (traffic) would not be applicable to the interior of a dwelling. Its presence in the exhaled air of smoke-free dwellings would be a clear indicator of outdoor pollution entering the building and concentrating there through ventilation.

These data and other comparable ones can lead us to the conclusion that controlling the ventilation of buildings and dwellings, and especially adjusting this ventilation to outdoor air conditions (by increasing or decreasing the exchange depending on indoor/outdoor pollutant differentials), is critical to ensure the best possible indoor air quality. Perhaps the new revolution at Building will come from low-cost distributed sensing: a natural evolution of what is already practiced in garages or boiler rooms (monoxide detection) but extended to all dwellings.

In fact, in 2016, WHO published a statistical report graduate "Health monitoring for the Sustainable development Goals", which defines as goal by 2030 to reduce the mortality rate attributed to household and ambient air pollution. It states that among the main obstacles to reducing mortality levels caused by air pollution is "...the lack of monitoring of air pollution levels, sources and public health consequences (...) to improve health and equity at subject health."

Knowing in detail how buildings contribute to pollution in cities would give public authorities, decision-makers and managers the tools to establish strategies to, for example, minimize the emission of pollutants into the atmosphere by mimicking the action of vehicle catalysts on fossil fuel engines, or to recover useful components such as waste methane, which could be redirected to energy generation.

This article was originally published in The Conversation. Read the original.