The secrets of healthy indoor air

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We discussed the factors to be considered to ensure that the air in our living spaces is healthy with Paolo Ciccioli, associate researcher at the Biological Systems Institute of the Italian National Research Council (CNR).

Which substances are most harmful for healthy interiors?

There are two main classes of contaminants that need to be controlled in indoor air: particulate matter (PM10 and PM2.5), which also include fungi and bacteria, and volatile organic compounds (VOCs), a category that comprises thousands of substances, which cannot all be eliminated by the same methods. Of course, priority has to be given to the most toxic VOCs. Indoor contaminants also include viruses, which are disseminated in relatively large droplets (from 5 to 5000 micron) and can therefore be eliminated using the same systems as PM2.5 particulate matter.

The market offers a variety of dynamic treatment systems for the removal of indoor contaminants (filtration and purification plants), but the main problem is that there is no method available for verifying their real performance levels. This will be the challenge for the coming years: the definition of an international method for certifying their fields of application and relative efficacy.


What can we do to be reasonably confident that our living spaces are healthy?

Readers should not be overly concerned. If the surfaces inside a home are cleaned with substances such as sodium hypochlorite, hydrogen peroxide or steam, and rooms are ventilated frequently, the build-up of toxic substances with which we come into contact is very low, and health risks are greatly reduced. It is also beneficial to install bacteriostatic and bactericide materials to guarantee the constant hygiene of shelves, walls and floors, although of course they will still require regular cleaning.

Ozone can also be used to sanitise indoor air, but it must be applied at high concentrations, so the room must be thoroughly ventilated after the treatment. UV-C radiation is another system that is effective but potentially harmful for man: it cannot be used when people are present and it does not work in shadow zones.


Where do treatment technologies have to be used to guarantee good air quality levels?

The use of dynamic air treatment systems is recommended in places used by large numbers of people – such as offices, supermarkets, stations, airports and production plants, and on public transport. These systems may be free-standing or centralised, integrated in HVAC plants. They are also recommended in homes in polluted urban areas, where opening the windows does not always reduce contaminant levels.

There are many technologies available nowadays: filtration using solid filters or liquid solutions, or treatment with ionising cold plasma and UV-C radiation. However, the spectrum and variety of contaminants are so vast that no one of these methods on its own is able to purify and sanitise indoor air completely. Therefore, systems that use several technologies simultaneously are currently being developed and produced.