The virus that causes COVID is found in the particles that we exhale out in our breath, as we speak, sing, cough, sneeze, or eat. The particles come out and scatter out in front of our faces and out beyond our faces. These particles are what spread the virus from person to person.
Some of these are tiny, and can float and move in the air. These tiny particles are called “aerosols.” Aerosols can float in the air for hours. In an unventilated space occupied by a person (such as a room with closed windows and no airflow and no air purifier), the amount of aerosols in the air can build up over time. Important: Aerosols are released even during normal breathing! (but accumulates up to 10 times more when speaking or up to 50 times more when shouting, singing, or coughing). A person in close contact with an infectious person, or sharing an unventilated indoor space with them, can inhale the Covid-19 virus-laden aerosol when they breathe, and be at risk of getting infected themselves. This is now considered a predominant form of transmission. Many health organizations, such as the World Health Organization (WHO), have recently revised their guidelines to emphasize COVID transmission via aerosols.
Using specialized cameras and lasers, and via simulations, this video shows how aerosol spreads in closed spaces when people talk or cough, and how ventilation helps clear the air of aerosol: https://youtu.be/H2azcn7MqOU
Here is another link that shows how the virus laden aerosol can build up in closed spaces such as a room or a bar or a car.
Many spaces that people frequent (or frequented before the current second wave of COVID) did not have good ventilation. And the state of ventilation is dynamic - it depends a bit on how many people are occupying the space, what they are doing in that space etc. (e.g., lots of people just standing would have different needs than if they were all talking, versus if they were all exercising).
It would be AWESOME, if there was way to monitor the aerosol levels in the air easily, cheaply, so that many shared spaces can be made safe. Often this is done via carbon di-oxide (CO2) as proxy – since we are also exhaling that, and CO2 also tends to build up in closed spaces, people have advocated for using CO2 as a proxy for understanding if a space is suitably ventilated.
Problem is CO2 meters are expensive. They can easily cost Rs.20,000 - not an easily justifiable expense by everyone, or owners of smaller establishments.
So, the challenge is to design a low-cost CO2 meter, or any other low cost way of measuring the aerosol concentration in the air. Cost, portability, access to parts and materials on the indian market, and ease of assembly, will all be important criterion.