Are you ventilating your house well?

Air pollution is one of the factors that most influence human health. According to the WHO, the risk of suffering from some types of cancer, diabetes, cognitive impairment, neurological diseases and premature birth is related to exposure to air pollution. And one of the atmospheric polluting agents regulated according to health protection criteria is nitrogen dioxide (NO2), which is especially relevant in urban environments such as the city of Madrid in Spain, due to the high density of road traffic, one of its main emission sources.

We are all aware that the air we breathe when we are outdoors may have a greater or lesser presence of polluting agents, but what happens when we are indoors? Is pollution also transported to these and at what levels? How should we ventilate the interiors to avoid this? These are some of the questions that a team of researchers has tried to answer, proposing an innovative methodology to evaluate the quality of the air we breathe in indoor spaces using digital twins of buildings and numerical modeling techniques.

The team is made up of specialists from the Polytechnic University of Madrid (UPM), the Center for Energy, Environmental and Technological Research (CIEMAT), the Complutense University of Madrid (UCM) and the University Institute of Marine Research (INMAR) of Cádiz, in Spain all these institutions.

These researchers have analyzed the impact of meteorological conditions on gas exchange between outdoor and indoor spaces, taking nitrogen oxides (NOx) from traffic as an example, with the aim of determining how interiors should be ventilated to minimize their impact.

To evaluate the quality of the air we breathe, data on the concentration of polluting agents from air quality monitoring stations located in cities is traditionally used, something that researchers consider insufficient.

“In urban environments, the spatial representativeness of these measurements is limited. This is because the interaction between the atmosphere and urban structures gives rise to very complex atmospheric flows at the local level, which cause very heterogeneous distributions of polluting agents within the streets. Furthermore, although people spend more than 90% of our time indoors, these are not usually taken into account in the assessment of exposure. That is why, to better evaluate the total exposure to atmospheric pollution, it is necessary to also consider these microenvironments,” explains Esther Rivas, Margarita Salas UPM postdoctoral researcher at the CIEMAT Atmospheric Modeling Unit and lead author of this work.

An innovative model

With the aim of also evaluating what happens to the air we breathe when we are under cover, the researchers applied a Computational Fluid Dynamics model to a digital twin of the San Carlos Clinical Hospital building in Madrid and its surroundings.

“Our main objective was to provide a better understanding of the impact of meteorological conditions on the outdoor-indoor NOx exchange through natural ventilation through numerical simulations at very high spatial resolution,” explains Rivas.

Their results indicate that the combination of an adequate atmospheric turbulence model, together with adequate boundary conditions, makes it possible to reproduce the temporal evolution of meteorological variables such as wind speed and direction, or turbulent kinetic energy, both at street level. such as on the roof of buildings, even when the wind speed is low. Furthermore, it makes it possible to reproduce the temporal evolution of NOx concentrations, both outdoors and indoors, particularly when the urban background concentration is considered from the data provided by air quality stations.

The data obtained is clear: to minimize the concentration of polluting agents from traffic inside buildings, natural ventilation should be carried out during hours of low concentrations of atmospheric polluting agents, avoiding peak hours in the morning and the afternoon.

It is not always a good time to open windows and ventilate interior spaces. (Photo: NPS/Suzanne McCarthy)

“One way to promote natural ventilation in urban environments would be to reduce pollutant concentrations near windows, for example by implementing measures to reduce traffic around buildings, especially in areas with sensitive populations, such as hospitals, schools, nursing homes. elderly, etc. In cases where these types of measures cannot be implemented, it would be interesting to promote the use of systems that allow the natural ventilation of buildings to be intelligently managed (that is, during the hours in which the quality of the outdoor air is more favorable), as well as the use of less polluting engines,” add the authors of the study.

The work has been framed within the AIRTEC-CM project (comprehensive evaluation of urban air quality and climate change), coordinated by Rafael Borge of the UPM, whose main objective is to understand the interactions and interdependencies between biotic, abiotic and meteorological factors in a context of changing climate in order to advance the knowledge of people’s exposure to air pollution in cities.

For the authors of the study, the importance of this study lies in the fact that “it has developed a methodology that could be applied to estimate the quality of the air we breathe both outside and inside buildings and that would help the design and evaluation of measures to reduce the population’s exposure to air pollution.

The study is titled “Indoor-outdoor NOx modeling in a single-side naturally ventilated room in a real building in Madrid”. And it has been published in the academic journal Journal of Building Engineering. (Source: UPM)