Blog series #3: How SARS-CoV-2 spreads through the air

Dr. Ajit Ahlawat is a postdoc at TROPOS – Leibniz Institute for Tropospheric Research in Leipzig. In his research he investigated the role of aerosol particles in the (indoor) spread of SARS-CoV-2

Name / Institute: Dr. Ajit Ahlawat
TROPOS – Leibniz Institute for Tropospheric Research Leipzig
Leibniz Section E

Research topic: Hygroscopicity measurement of ambient aerosol particles

Main featured instrument or technique: Measurement of hygroscopicity (water uptake) of aerosol particles with a HTDMA (Hygroscopicity Tandem Differential Mobility Analyzer).

“I explored the role of indoor relative humidity in airborne transmission of SARS-CoV-2”

What was your main research topic in the last 1-2 years before spring 2020?

Even before COVID-19 came into all our lives my main research topic has been the measurement of the water uptake ability (“hygroscopicity”) of ambient aerosol particles. For this purpose I mainly use an instrument called Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) at 90% relative humidity. For calibration and inter-comparison I also work with other aerosol instruments such as the Condensation Particle Counter (CPC), Scanning Mobility Particle Sizer (SMPS) and Faraday Cup Aerosol Electrometer (FCAE).

What are the main findings of your work on COVID? Did the results surprise you or did they basically confirm what you had thought before you started this study?

Air humidity influences the spread of corona viruses indoors in three different ways: (a) it affects the behaviour of microorganisms within the virus droplets, (b) it changes the survival or inactivation of the virus on the surfaces, and, (c) dry indoor air plays a crucial role in the airborne transmission of viruses. For instance, if the relative humidity of indoor air falls below a certain threshold, i.e. 40%, the particles emitted by infected people absorb less water, remain lighter, fly further through the room and are more likely to be inhaled by others. This means that in very dry indoor places with a relative humidity below 40%, the chances of airborne transmission of SARS-CoV-2 are much higher than in humid places with around 90% relative humidity. In addition, dry air also makes the mucous membranes in our noses dry and more permeable to viruses.

Based on our research we were surprised to see how low relative humidity indoors can have strong effects on the survival of microorganisms including SARS-CoV-2 in aerosol particles and droplets.

How has COVID-19 affected your life?

The majority of my research work at TROPOS basically involved laboratory measurements of aerosol particles. In the pandemic times, I had to juggle partially working from home while also regularly conducting experiments in the laboratory. This was quite a challenge. But in the end I have to say that after more than a year of home office it is now becoming adaptable for me despite the new work culture.

I would also say that the past one and a half years of COVID-19 have provided good opportunities to spend more time with my family. On the other hand working from home with a small kid can be sometimes overwhelming.

You have managed to hook your research into the incalculable emerging pandemic. What is your advice for postdocs that want to embrace such a challenging research topic?

Indeed, the research topic is challenging and my advice for postdocs is that there are further requirements for experiments and modeling in order to get more detailed information on seasonal variations of indoor humidity and virus transmission. Another important and more general advice for aerosol researchers is to build on and expand collaborations with virologists, epidemiologists and other specialists to further our understanding of the spread of viral diseases. I think this is crucial for the mitigation of the COVID-19 pandemic but also for other diseases caused by airborne microbes.

What would be the one take-home message of your research?

Use humidifiers, particularly during wintertime, which will keep the indoor relative humidity maintained at 40-60%. In summertime you should open windows for natural ventilation in absence of mechanical ventilation, use N95 masks regularly and keep on avoiding mass gatherings.

How does your perfect day off work look like?

A perfect day is a day spent with my family. In COVID-19 times it’s also much better to spend most of that time outdoors and stay away from mass gatherings.

 We would like to express our sincere thanks to Dr. Ajit Ahlawat for supporting our new blog interview format with active participation.

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