Plants, natural fibre ionisers effective in reducing Covid-19 droplets transmission: Study

Plant and natural fiber ionisers are most effective in reducing aerosols from the air in poorly ventilated spaces.
Plant and natural fiber ionisers are most effective in reducing aerosols from the air in poorly ventilated spaces.PHOTO: A*STAR

SINGAPORE - Researchers looking at ways to reduce the risk of Covid-19 transmission have found that plants, 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, organisations, as well as families and individuals to explore what best fit their needs and circumstances, said the agencies in a release on Thursday (Feb 25).

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, the Agency for Science, Technology and Research (A*Star) and other research partners such as ITE College East and Temasek Life Sciences Laboratory (TLL), 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 in various venues such as public transportation, concert theatres, offices and eateries.

"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 (Mice) activities."

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

Ionisers purify the air by generating negative ions, by charging 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 to a normal plant."

Their experiments showed that the plant ioniser was able to reduce the number of aerosol particles in a room from 4,000 particles per cubic cm to 100 particles per cubic cm in the span of six minutes, compared with 25 minutes without an ioniser.


An air filter can effectively capture and inhibit microbes such as bacteria and viruses found in aerosols. PHOTO: A*STAR

They also found that air filters can effectively capture microbes such as bacteria and viruses found in aerosols.

When used in 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 with high risk especially if there is prolonged contact.

However, the volume of air in an MRT train cabin is changed every six minutes, "notwithstanding the opening and closing of the train doors", said Dr Kang Chang Wei.

He is a senior scientist and deputy director of the Fluid Dynamics team at A*Star's Institute of High Performance Computing (IHPC).


Table-top dividers can reduce the spread of droplets when people remove their masks during meals. PHOTO: A*STAR


Ultraviolet-C (UVC) light rays inactivate coronaviruses with adequate exposure time and intensity from the UVC source. PHOTO: A*STAR

"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 droplets transmission.

However, the researchers stressed that these solutions are "additional levels of defence" to reduce transmission risks through surfaces, droplets and aerosol routes.

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 toolkits which could help reduce our risks during the next unknown Disease X which could have aerosol as its main route of transmission."

Safe management measures including mask wearing, maintaining one-metre safe distancing, and having good personal hygiene remains as the first line of defence in curbing the spread of the Covid-19 virus.