New Delhi, Aug 21 (IANS): An Indian-German team of scientists has found that the airborne transmission of Covid-19 virus via aerosol particles in the indoor environment seems to be strongly influenced by relative humidity.

According to the researchers, including those from CSIR National Physical Laboratory in New Delhi, the conclusion drawn from the analysis of 10 most relevant international studies on the subject.

In addition to measures like social distancing and wearing masks, the researchers recommended controlling indoor humidity conditions to contain the Covid-19.

The research team revealed that relative humidity of 40 to 60 per cent could reduce the spread of the viruses and their absorption through the nasal mucous membrane. It is therefore extremely important to implement standards for indoor air humidity in rooms with many people, such as hospitals, open-plan offices or public transport, the study, published in journal Aerosol and Air Quality Research, reported.

According to the study, researchers have now been able to prove that tiny drops of five micrometres in diameter, such as those produced when speaking, can float in the air for up to nine minutes.

"In aerosol research, it has long been known that air humidity plays a major role: The more humid the air is, the more water adheres to the particles and so they can grow faster," said study researcher Ajit Ahlawat from the Leibniz Institute for Tropospheric Research (TROPOS) in Germany.

"So, we were curious: what studies have already been conducted on this," he explained.

The results showed that air humidity influences the spread of coronaviruses indoors in three different ways: (a) the behaviour of microorganisms within the virus droplets, (b) the survival or inactivation of the virus on the surfaces, and (c) the role of dry indoor air in the airborne transmission of viruses. Although low humidity causes the droplets containing viruses to dry out more quickly, the survivability of the viruses still seems to remain high.

"If the relative humidity of indoor air is below 40 per cent, the particles emitted by infected people absorb less water, remain lighter, fly further through the room and are more likely to be inhaled by healthy people," Ahlawat said.

"In addition, dry air also makes the mucous membranes in our noses dry and more permeable to viruses," he added.

The new findings are particularly important for the upcoming winter season in the northern hemisphere when millions of people will be staying in heated rooms.

"Heating the fresh air also ensures that it dries. In cold and temperate climate zones, therefore, the indoor climate is usually very dry during the heating season. This could encourage the spread of coronaviruses," the authors warned.

This week, another study published in the journal Transboundary and Emerging Diseases, found that low humidity, dry air can increase the risk of Covid-19 virus.