ALMOST everyone knows that the SARS-CoV-2 virus is airborne, that it could be transmitted through very tiny particles suspended in the air called aerosols. For the longest time, the Department of Health (DoH) got stuck with their “Mask, Hugas, Iwas, Bakuna.” But as part of its holiday reminders, the DoH added airflow to its slogan on Covid-19 prevention, probably to acknowledge that stagnant air eases virus transmission. Telling people to open their windows and allow fresh air in is not enough. Aside from getting the vaccines and other interventions, health protocols need to stress the use of well-fitted masks, ventilation and air filtration.

In an article, “With Covid-19, Air Is Both the Problem and the Solution,” written by Jonathan Jarry, a question is raised. How is ventilation adequate in any room? To assess potential SARS-CoV-2 aerosols, a nondispersive infrared (NDIR) carbon dioxide (CO2) sensor could be used, suggests Jarry. “You want the air in your house [or indoors] to be as fresh as the outdoor air,” added Professor Kimberly Prather, an atmospheric chemist at the Scripps Institution of Oceanography and UC San Diego, who studies aerosols. “We humans breathe air in, hold onto the oxygen, and breathe out CO2. An NDIR CO2 sensor uses a specific beam of infrared light that CO2 molecules love to absorb. The more CO2 in the detector, the less infrared hits the sensor. The device translates this into the amount of CO2 present in the air in parts per million (ppm). When people release CO2 into a shared room, that number creeps up. All that means is that you are breathing other people’s shared breaths. We don’t want that.”

The CO2 detector could not tell you if the virus is present in the air. But if the virus is present, large quantities of CO2 mean ventilation is inadequate. Those aerosolized viruses are not leaving the room anytime soon. “As a rule of thumb, if a room has between 600 and 800 ppm CO2, that’s pretty good. Over 1,000 ppm, that is an indicator that ventilation is insufficient,” Professor V. Faye McNeill affirms. McNeill does research on aerosols and air quality in the Department of Chemical Engineering at Columbia University.

I bought a CO2 detector at Shopee during the holidays and brought it with me to the supermarket and the drugstore. Most of the places I visited showed CO2 levels at above 1,000 ppm. Ventilation at home was at 400 ppm. Anything above 1,000 ppm prompted me to wear a double mask just to be safe. My friends and I share pictures of our CO2 sensors when we visit malls and other enclosed spaces on the Facebook page of Healthy Indoor Spaces (Medical and Health). A friend reported to me that CO2 levels in his office reached over 2,000 ppm. “No wonder I got Covid-19 three times,” he exclaimed. Are workplaces even following the Department of Labor and Employment (DoLE) Order 224 issued on March 3, 2021, on the “Guidelines on Ventilation for Workplaces and Public Transport to Prevent and Control the Spread of Covid-19?” Quantitative assessment notes that “CO2 is commonly used as a surrogate indicator for assessing indoor air quality (IAQ) and ventilation efficiency. CO2 concentration shall not exceed 1,000 ppm.”