Portable air filters and HVAC filters can reduce indoor air pollutants, including viruses, that are transmitted through the air. However, they alone are not enough to protect people from the virus that causes COVID-19. To understand the basics of air purifiers, why face masks really work, and how chemical experiments and computer simulations in the laboratory translate into environmental policies, we spoke to aerosol scientist Faye McNeill, a professor of chemical engineering at Columbia University who studies aerosols. Aerosols are airborne microscopic particles that include everything from dust to viruses and smog. As a college student at Caltech in the late 90s, McNeill was fascinated by aerosols and their role in environmental and public health policy.
He learned that air pollution is anything but simple at the molecular level. Los Angeles had tried since the 1940s to reduce its ozone levels, but it took more than a decade before scientists understood the cocktail of emissions that leads to smog. And more decades before catalytic converters were added to vehicles to address the root of the problem. Smog is formed when nitrogen oxides and volatile organic compounds in automobile exhaust and other emissions react with light.
McNeill discussed air filtration and best practices with us, and how the pandemic has changed his teaching and perspective on aerosols. He explained that HEPA filters can trap particles containing coronavirus, as people expel respiratory fluid droplets, saliva, and possibly viruses into the air when breathing, coughing, and talking. Even if the water in the drop evaporates, the droplets contain salts, proteins and other materials in addition to any viruses, which means that the remaining particles are usually a few microns in size, making them quite easy to trap with a HEPA filter. McNeill also discussed other types of air filters that can help remove particulates from indoor air.
A homemade air purifier called “Corsi-Rosenthal Box”, consisting of an HVAC filter and a box fan, is quite effective. He recommends placing an air purifier as close as possible to the center of the room without obstructing airflow. If it's a classroom with a 20-minute break between classes, he suggests leaving it on but turning it off at night. People should look for an air purifier that is the right size for their room.
McNeill shared that he now thinks much more about indoor air quality and the fundamental role of ventilation since Covid-19 began. He is giving a mandatory class this fall for chemical engineering students called “Chemical Process Control” and will be wearing a mask. He also discussed how pre-filtering the air with low-cost, high-dust filters of lower efficiency can extend the lifespan of a HEPA filter. The use of masks without air filters reduced aerosol exposure of receivers by 72%, and the use of air filters without masks reduced exposure by up to 65%.
While the FDA has not yet verified these claims, results suggest that EnviroKlenz's air cartridge could be an effective way to capture and filter pathogens similar in size to the coronavirus. The team chose high-efficiency particulate air (HEPA) filters which expel air through a fine mesh that traps extremely small particles. While most MERV filters have a fractional efficiency level for particles as small as the coronavirus (0.1 micron), HEPA filters with a European rating of H 14 or higher are recommended for optimal protection against airborne transmission of Covid-19. Results suggest that air filters could be used to reduce the risk of patients and medical staff contracting SARS-CoV-2 in hospitals. The best air purifiers can go a long way in eliminating dangerous germs and bacteria from the air.
The Dyson Purifier Cool TP09 is an example of an advanced cold air purifier that works like an expertly designed bacteria filter.
