Coronavirus Singapore

Plant, natural fibre ionisers can curb aerosol transmission: Study

They are effective at lowering aerosol concentrations in the air, researchers find

Researchers looking at ways to reduce the risk of Covid-19 transmission have found that plant and natural fibre ionisers and air filters are effective in reducing aerosol concentrations in the air, and can take safe management to the next level.

The Agency for Science, Technology and Research (A*Star) and Temasek Foundation, working with research agencies here, have come up with a new handbook of measures that individuals, families and companies can take, as the nation opens up further.

These solutions are now being offered to businesses and organisations, as well as families and individuals, to explore what best fits their needs and circumstances, the agencies said in a release yesterday.

Aside from air filters in homes and offices to reduce the spread of small respiratory droplets, or aerosols, researchers have looked at other solutions, including table-top dividers in food court settings.

"Temasek Foundation, A*Star and other research partners such as ITE College East and Temasek Life Sciences Laboratory have done extensive scientific studies in collaboration with public agencies, and gleaned insights which could be useful in further reducing the risk of Covid-19 transmission," said the foundation.

Tests were conducted at various venues such as concert theatres, offices, eateries and on public transportation.

"For instance, A*Star worked with the Land Transport Authority to model the dissemination of aerosols in public transportation, and developed recommendations to reduce the spread of aerosols.

"Similar works have been carried out with the Singapore Tourism Board to facilitate the safe resumption of meetings, incentives, conferences and exhibitions activities," said the foundation.

Dr Ady Suwardi, deputy head of soft materials at A*Star's Institute of Materials Research and Engineering (IMRE), said the researchers found that plant and natural fibre ionisers were the most useful in reducing the concentration of aerosol particles in poorly ventilated indoor spaces.

Ionisers purify the air by generating negative ions that charge up aerosol particles, which then stick onto surfaces such as the floor and the walls.

These surfaces will then have to be cleaned regularly and thoroughly to reduce the risk of fomite transmission, which is when an article or surface has become contaminated.

Professor Loh Xian Jun, executive director of the IMRE, said: "Plants are naturally able to generate ions, so when it is fitted with an electrical ioniser device, the plant is stimulated such that it is able to emit up to a million times more ions compared with a normal plant."

They also found that air filters can effectively capture microbes such as bacteria and viruses found in aerosols. When used on fans and air conditioners, the filters can help to purify indoor air and reduce the spread of aerosols.

Based on A*Star's airflow modelling and simulation studies, the researchers found that the spread of droplets and aerosols is dependent on the different types of ventilation environments of each venue.

Environmental conditions such as wind speed and direction, humidity levels, air temperature and ventilation levels in indoor spaces could affect the concentration levels of aerosol particles lingering in the air.

Aerosols, the researchers found, can stay suspended in the air for hours or be carried by wind or currents from air conditioners or fans for some distances.

They added that most automobiles and cars do not have sophisticated air cleaning systems and can be venues of high risk especially if there is prolonged contact.

However, Dr Kang Chang Wei, a senior scientist and deputy director of the fluid dynamics team at A*Star's Institute of High Performance Computing, noted that the volume of air in an MRT train cabin is changed every six minutes, "not withstanding the opening and closing of the train doors".

"The ventilation in spaces such as the MRT train cabins is usually better as it uses a centralised air conditioning system, which constantly filters the air in the cabin and supplies it with fresh outdoor air," he added.

The researchers also looked at other solutions such as disinfecting surfaces with ultraviolet light, and found that it can help to inactivate different types of bacteria and viruses.

They said table-top dividers can also reduce droplet transmission.

However, the researchers stressed that these solutions are "additional levels of defence" to reduce transmission risks through surfaces, droplets and aerosol routes. Safe management measures including mask-wearing, maintaining 1m safe distancing and having good personal hygiene remain as the first line of defence in curbing the spread of the Covid-19 virus.

Ms Koh Lin-Net, chief executive of Temasek Foundation Nurtures, said: "Wearing masks, practising hand hygiene and keeping safe distancing have become norms.

"But as the situation continues to evolve, we must also continue to add to our knowledge base.

"These would not just be useful to reduce Covid-19 transmission risks, but will also give us tool kits which could help reduce our risks during the next unknown 'Disease X', which could have aerosol as its main route of transmission."

A version of this article appeared in the print edition of The Straits Times on February 26, 2021, with the headline 'Plant, natural fibre ionisers can curb aerosol transmission: Study'. Subscribe