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The end of the COVID-19 pandemic doesn’t seem near. However, whenever it does end, our lifestyle would not go back to being what it was in the pre-pandemic era within a day. Just as we are doing now, most of us will have to continue working remotely. Children may also have to continue online education from home, while indoor spaces outside of our homes like restaurants, offices, gyms etc will have to ensure that they do not let their guard down at once considering the gravity of the situation.

Most of us continue to spend almost 95% of their time indoors. Unfortunately data shows that chances of COVID transmission are significantly higher indoors than outdoors. A study conducted in April last year found that people were more likely to catch coronavirus infection indoors than outdoors. It claimed that sharing of indoor space is a major SARS-CoV-2 infection risk.

Staying indoors, lack of exposure to sunlight, limited physical activity and lack of exposure to regular germs that we are usually exposed to outdoors has also weakened our immunity thus making us more susceptible to catching infections.

Increased risk of Infection

When we think of a closed environment, most of us envision comfortable spaces, shared or otherwise, that provide us with an environment worthy of working, living or spending long duration. These criteria hold true even for spaces which may not be a part of our day to day life like offices and homes are- such as restaurants, coffee shops, taxis, metros, cinemas, malls and meeting halls.

However, the air quality in these indoor spaces can be breeding ground for infection, or particles that can make us susceptible to sickness.

When it comes to indoor air quality and COVID infection risk, here are five key parameters that you should care about.

CO2 and ventilation

People living in the same household are prone to catching infection from each other. Keeping doors and windows closed all the time only increases the risk further due to poor ventilation and lack of fresh air.

With evidence increasingly pointing towards airborne transmission being a major factor in the spread of the virus, the inference is that CO2 levels in rooms and other enclosed spaces may be used as a proxy for COVID-19 transmission risk.

The poorer the ventilation, the longer the virus stays trapped indoors and the viral load in the indoor air continues to increase as an infected individual continues to exhale in the same indoor air. The higher the viral load indoors, the greater the chance of infecting another healthy individual in the shared environment.

CO2 levels in an indoor environment is a good proxy for the ventilation levels in the indoor space. Outdoor CO2 levels globally are at approximately 400ppm. As individuals exhale indoors, they release CO2 in the air, causing CO2 levels to increase beyond 400ppm. Ventilation enables mixing of indoor air with outdoor air, helping CO2 levels to slowly reduce and settle closer to 400ppm. Higher the ventilation, lower the CO2 levels and vice versa. A research by University of Colorado at Boulder conducted in April 2021 suggests that in any given indoor environment, when excess CO2 levels double, the risk of transmission doubles as well.

In fact various studies and scientists around the world are now using CO2 measurement as a proxy for virus transmission indoors.

It is hence more important than ever to ventilate your homes regularly, and ensure that any restaurant or building you go to is monitoring CO2 levels and ensuring levels stay within 800ppm or at most 1100 ppm to reduce transmission of virus amongst occupants.

Humidity and Temperature

A study’s findings revealed that temperature and humidity were inversely correlated with daily new cases and deaths of COVID-19. For every 1 °C increase in temperature, daily new cases of COVID-19 reduced by 3.08% and daily new deaths reduced by 1.19%; for every 1% increase in humidity, daily new cases of COVID-19 reduced by 0.85%, and daily new deaths reduced by 0.51%, according to analyses of 166 countries. Clearly temperature and humidity seems to have a huge impact on the survivability of the virus.

Survivability: A recent study found that maintaining indoor relative humidity >40% significantly reduces the infectivity of the air-borne virus. Another study claims that maintaining a Relative Humidity of 50 percent lessens the risk of being infected by SARS-CoV surrogate viruses as it leads to faster virus inactivation.

The study further elaborates that in dry air, that is with relative humidity as low as 20 percent, coronaviruses may be able to survive over surfaces for a week.To sum it up, improved humidification in indoor spaces like offices and homes can reduce the viability of the viruses to less than one percent in a span of two days, thus drastically bringing down the risk of infection.

The above stated study also sheds light on the role of air temperature in virus inactivation. According to it, viruses were inactivated more rapidly at 40°C than at 20°C. The study found that at 4°C, infectious viruses persisted for as long as 28 days.

Airborne longer: According to a study from University of Sydney when the humidity is lower, the air is drier and it makes the aerosols smaller, when you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.

Reduced immunity: A recent article also suggests that in addition to the survivability of the virus, our immunity to the virus also reduces at lower humidity levels. The hair-like organelles outside of cells that line the body’s airways, called cilia, do not function as well in dry conditions — thus they cannot expel viral particles as well as they otherwise would.

This implies the need to constantly keep monitoring and managing indoor temperature and humidity levels as they could have a much larger impact on our wellness than we are willing to give them credit for. It is also notable that very high humidity levels of greater than 60% can lead to mold development, and very high temperatures can be uncomfortable so it's important to maintain humidity in the 40-60% range and temperature in the range of 24-30 deg C so it continues to be comfortable and healthy.

PM 2.5

A recent study conducted across 721 districts of India has correlated high levels of PM 2.5 with increased susceptibility to contracting COVID-19 infection and resulting deaths. Bad air quality days have a visible relationship with the number of COVID-19 casualties, claims the study.

Another study published in Harvard University shows that an increase of 1 microgram per cubic metre in PM 2.5 leads to an 8% increase in death rate due to COVID-19.

PM2.5 particles in the air may also be causing the virus to stay airborne longer increasing risk of infection. An NCBI study notes that “fine particulates prolong the atmospheric lifetime of infectious viruses, thus favouring transmission.” COVID virus may latch onto PM2.5 particles in the air causing them to stay air-borne for relatively longer duration and spread further.

Hence monitoring PM2.5 in indoor environments and ensuring that it stays within safe levels of ideally less than 15ug/m3 or upto 30ug/m3 (in high pollution days) is a must.

Total Volatile Organic Compounds (TVOCs)

One of the big side effects of COVID is the increased use of sanitizers and cleaning products in offices and homes. A substantial number of scientific studies now have found that chemicals, including VOCs, emitted from cleaning and sanitizing products may have health effects, primarily in those using the products professionally, but also in those doing domestic cleaning in their own homes.

Regarding domestic cleaning, a study had found that a high frequency of using spray products during household cleaning (especially glass-cleaning and furniture sprays and air freshening sprays) was associated with a 40% increase in wheeze, a 50% increase in asthma symptoms or medication use, and approximately a 100% increase in incidence in physician-diagnosed asthma.

It is hence extremely important to monitor VOC levels in homes and office buildings and be more cognizant of overuse of cleaning and sanitizing products. Learn more about VOCs here.

Managing your exposure in Indoor environments

It is very important that when we are in public indoor spaces like restaurants or malls, we make sure we mask up and observe social distancing, but even at home we can take precautions to ensure that if there is any exposure at home from a family member or part time help or guest, it doesn’t transmit to the whole family.

In offices, restaurants etc. the facility manages can also take greater precautions to reduce transmission of virus indoors.

At home

• Constantly monitor air quality indoors. We recommend monitoring PM2.5, CO2, Temp and humidity and TVOC also optionally. Check out our PM2510CTH-T monitor which enables you to monitor these parameters easily.

• Ventilate your home naturally, especially during the day when air quality outdoors is clean. Open your windows and ensure that your CO2 and TVOC levels are within limit.

• Reduce use of aerosol sprays, toxic cleaning chemicals which might worsen air quality

• Usage of indoor plants helps with keeping air indoors fresh and removing VOCs from the air but often plants can also lead to increased humidity, so do monitor humidity levels and ensure they are within 50-60%. Use humidifiers or dehumidifiers to keep humidity within range in very high or low humidity months.

• Maintaining higher temp (that is still comfortable 24-30 deg C) and humidity (40-60%) which can ensure faster inactivation of virus in the indoor environment.

• Ensuring PM 2.5 levels are within limits by avoiding smoking or lighting agarbattis in the house, using proper exhaust while cooking and using purifiers when air quality outdoors is very poor.

• Ensure that any member of the family showing symptoms of COVID-19 or any other communicable diseases is immediately isolated.

• If housemates have to share common spaces or bedrooms, despite showing symptoms of communicable infection, encourage use of face masks.

• Plan to meet with friends in open spaces instead of in indoor spaces.

• Use double masks in shared spaces like lifts, apartment lobbies.

• Maintain social distance, especially when the number of cases soar in your locality or city, to avoid the risk of spreading infection.

At your workplace

Here are some guidelines by WHO on how to prepare your office for bringing employees back to work. In addition it is important to note that given covid is air-borne special precautions indoors can drastically reduce intra-office transmission.

• Employers must encourage use of face masks and shields at all times.

• Employees must practice social distancing even at the workplace and especially canteens and kitchens where they may be taking their mask off.

• Encourage your employers to monitor air quality at all times and ensure that air quality is conducive to low viral transmission between employees.

• Employers should encourage work from home to keep workplace strength limited. They may also employ strategies like odd-even days etc, to cut down the strength at work place by one half or two thirds on any given day.

Image Credit: Times of India

In public spaces like restaurants and malls

• As much as possible try to go to open malls to shop, and eat at open restaurants rather than closed malls where a large number of people are gathering in a closed space.

• When inside shops or malls make sure you’re always double masked and keep social distancing from others.

• Check with shop or restaurant owners if they are monitoring air quality in their premises and ensuring proper ventilation and purification.

What are some of the other measures that can be taken according to you, to ensure good air quality at your living and working place in a post COVID-19 world?