Science needs to step up when it comes to air pollution

Making indoor spaces safer: The Belgian air quality laws in 2018-2025 and the ASHRAE rule in 2022 are a race against time

They now know about the consequences of dirty indoor air. It is still the low income and marginalized who are most exposed.

In 2025, Belgian consumers will get more information when restaurants and indoor workspaces show air-quality ratings in a certification system. Belgium’s rating system could help determine if a venue is closed during a future flu epidemic.

The boldest move that countries have made to make indoor spaces safer in the face of infectious diseases is the law that took effect in July 2022.

“We have always addressed indoor air quality, but not specifically for pathogen mitigation,” says engineer Ginger Scoggins, the president-elect of ASHRAE, who is based in North Carolina. ASHRAE could face some pushback. Many people in the warm part of the United States were upset when the society increased the Ventilation Requirement from 5 to 15 square feet per minute, since it would increase energy costs from air conditioning. Her local school board passed a ruling that its classrooms only needed to get to 7.5.

There are huge challenges ahead for the existing stock of schools, offices and other public venues. Retrofitting them with the technology to deliver clean air at sufficient levels will be an immense — and costly — undertaking, say experts in this field. They argue the benefits would outweigh the costs. By one estimate, pandemic and seasonal influenza outbreaks cost the United Kingdom £23 billion (US$27 billion) per year, on average (see ‘The high cost of outbreaks’), and the country could save £174 billion over a 60-year period by improving ventilation in buildings (see go.nature.com/3ktumeg).

Making indoor spaces safe from infection could also reduce exposure to pollutants such as fine particulates from wildfire smoke and cooking, volatile organic compounds leached from furniture, and allergy-causing moulds and pollen. It could increase energy costs, and contribute to greenhouse gas emissions.

Researchers say it will take time to lower the infection risks inside buildings. We’re looking at 30 years. We’re discussing the future of our society.

It is a race against time. As concern over COVID-19 wanes, experts wonder how much progress countries will make before the next big outbreak of an airborne infectious disease.

How much ventilation should school students bring in? An observational study of the effectiveness of air cleaners for low level of ventilation per person in classrooms

Such advice sowed confusion, says Joseph Allen, a building hygienist at the Harvard T.H. Chan School of Public Health in Boston, Massachusetts. He says that you cannot tell people to bring in more outdoor air without knowing how much.

Allen was one of the first to put a value on how much ventilation people should be aiming for. In June 2020, he and his colleagues recommended that schools wanting to reopen their doors after lockdowns should deliver four to six air changes per hour to their classrooms1 — changes in which the entire volume of air in the room is replaced. That amounts to a ventilation rate of 10–14 litres per second per person. Most schools were achieving much less than that, however. The study found that most classrooms didn’t meet the required level of air flow. The World Health Organization published new guidelines that recommend a 10 litres per second rate for people outside health-care settings.

Instead, researchers tried to gain clues through observational studies. Morawska was involved in one that looked at 10,000 school classrooms in the Marche region of Italy. In the 316 classrooms that had a rate of mechanical ventilating at a maximum of 14 liters per second per person, the students’ risk of infection was reduced by at least 70% over a four-month period at the end of the year. This group typically received less than 1 liter per person. When ventilation rates were at least 10 litres per second per student, the infection risk was 80% lower3.

There is evidence that other technologies can remove infectious particles from the air. A study4 was able to show the effectiveness of two air cleaners fitted with high efficiency particulate absorbing (HEPA) filters and put them in a 54-square-metre conference room with a dummy. Three dummy participants had their aerosol exposure reduced by the cleaners. That’s just shy of the 72% reduction achieved by masking all of the dummy participants4.

Ventilation requirements can be complicated, because they change depending on how big the space is, how many people are in it and how active they are. So some researchers advocate using a shortcut — setting maximum carbon dioxide concentrations. CO2 is often used as a proxy for indoor air quality. Because people exhale CO2 as they breathe, levels of the gas can shoot up if a space is crowded or if there is insufficient ventilation to replace the exhaled air — which might contain infectious viruses — with clean air.

A small study published in September 2022 — and yet to be peer reviewed — directly connected CO2 levels with those of infectious pathogens. The authors tested air samples in nurseries, schools, universities and care homes for the presence of respiratory pathogens. Rooms with higher levels of CO2 were associated with higher levels of respiratory pathogens.

Despite these issues, Morawska says that CO2 monitors should be widely deployed as an inexpensive, readily available tool that could be installed in every indoor space, much like smoke alarms. But displaying CO2 read-outs on its own is not enough, she adds, because it places the onus on room occupants to track air quality and decide what to do if readings are high.

Japan has a law that requires buildings to not exceed indoor CO2 concentrations of more than 1,000 p.p.m. If the air quality does not meet standards, the law requires that managers assess the air quality twice a month, report the results to the government, and then create a plan to correct the problem. In 2017, almost 30% of buildings exceeded the CO2 limit.

Still, the Japanese laws work, says Kazukiyo Kumagai, a public-health engineer at the California Department of Health in Richmond. “Japan is in a better condition” than the United States when it comes to indoor air quality, he says. He suggests adopting aJapanese-style approach of monitoring and reporting.

Allen says that despite ASHRAE standards not being enforced, they will make a difference. Businesses in older buildings will see a strong signal about the gold standard for indoor air quality from more stringent ASHRAE standards.