Special Issue on COVID-19 Aerosol Drivers, Impacts and Mitigation (V)

Ajit Ahlawat This email address is being protected from spambots. You need JavaScript enabled to view it.1, Alfred Wiedensohler1, Sumit Kumar Mishra2


1 Leibniz Institute for Tropospheric Research (TROPOS), Permoserstraße, 15 Leipzig, Germany
2 CSIR-National Physical Laboratory, New Delhi, India


Received: June 16, 2020
Revised: July 17, 2020
Accepted: July 21, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.2020.06.0302  

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Cite this article:

Ahlawat, A., Wiedensohler, A. and Mishra, S.K. (2020). An Overview on the Role of Relative Humidity in Airborne Transmission of SARS-CoV-2 in Indoor Environments. Aerosol Air Qual. Res. 20: 1856–1861. https://doi.org/10.4209/aaqr.2020.06.0302


  • RH is a factor responsible for airborne transmission of SARS-CoV-2 virus.
  • In dry indoor areas, chances of airborne transmission are higher than humid areas.
  • Indoor air at 40 to 60 percent RH is the optimum level for human health.
  • Important to set minimum RH standard for indoor environments.


COVID-19 disease is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which originated in Wuhan, China and spread with an astonishing rate across the world. The transmission routes of SARS-CoV-2 are still debated, but recent evidence strongly suggests that COVID-19 could be transmitted via air in poorly ventilated places. Some studies also suggest the higher surface stability of SARS-CoV-2 as compared to SARS-CoV-1. It is also possible that small viral particles may enter into indoor environments from the various emission sources aided by environmental factors such as relative humidity, wind speed, temperature, thus representing a type of an aerosol transmission. Here, we explore the role of relative humidity in airborne transmission of SARS-CoV-2 virus in indoor environments based on recent studies around the world. Humidity affects both the evaporation kinematics and particle growth. In dry indoor places i.e., less humidity (< 40% RH), the chances of airborne transmission of SARS-CoV-2 are higher than that of humid places (i.e., > 90% RH). Based on earlier studies, a relative humidity of 40–60% was found to be optimal for human health in indoor places. Thus, it is extremely important to set a minimum relative humidity standard for indoor environments such as hospitals, offices and public transports for minimization of airborne spread of SARS-CoV-2.

Keywords: Aerosol; COVID-19; SARS-CoV-2; Indoor; Humidity

Aerosol Air Qual. Res. 20 :1856 -1861 . https://doi.org/10.4209/aaqr.2020.06.0302  

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