MOUNT VERNON — Inside an airy, stained glass-adorned room at Salem Lutheran Church, the Skagit Valley Chorale is surrounded by reminders of deep heartbreak.

Four doorways are propped open, two to the cool, outdoor air. A pair of homemade air cleaners, fashioned from furnace filters, a box fan and duct tape, hum away at the center of the room. A laptop streams video via Zoom. Two small monitors gauge the concentration of carbon dioxide — and alert the choir when too much of their own breath accumulates.

These are some of the safety measures the Chorale now takes after the coronavirus visited them in March 2020, when a seemingly ordinary choir practice became one of the country’s first superspreader events.

More than 50 members were infected, at least a handful hospitalized. Two died.

“We were burned,” member Leigh Giovane said Tuesday evening, before weekly rehearsal had started. The Chorale only recently returned to indoor activities. “Because we had such a devastating experience, we felt we had to be as careful as we could with the lives of our members.”

The group’s experience ventilating and filtering indoor air illustrates a new stage of the COVID-19 pandemic that Washington, along with much of the United States, is moving toward after the omicron variant infected vast swaths of the population.

State and local health officials say this transition will be a key period to prepare for future health crises. Vaccinations and boosters remain some of the best tools for protecting against severe disease and death, but as public health mandates — like for masking — have ended, experts say some long-term, structural changes will become even more important.

Improving indoor air quality is one of those changes. But steep barriers stand in the way, particularly for small businesses and schools, leaving many questions around what steps communities will take.

“Indoor air ventilation is extremely important to reduce transmission of the virus,” said Shirlee Tan, a toxicologist for environmental health services at Public Health — Seattle & King County. “There are easy ways to do that, whether you have an HVAC (Heating, Ventilation and Air Conditioning) system or not. Just opening a window or door and letting in some outdoor air can do a lot.”

In Washington state, some air quality standards, set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, exist for different sectors, but there’s a huge need for new building codes and better statewide ventilation requirements, Tan said.

Studies show high-quality air ventilation systems help reduce transmission of airborne diseases, including COVID, by removing particles from indoor air. One study linked improved ventilation strategies in schools to a 48% lower rate of COVID.

Momentum appears to be shifting toward those efforts. The state Department of Health has committed to tackling the issue in its most recent pandemic plan by listing a number of recommendations, particularly for schools.

President Joe Biden this year also introduced a nationwide effort to improve ventilation in buildings, calling on schools and organizations to use federal relief — Washington received $1.8 billion — to adopt key strategies.

“Most of us spend 80% indoors, whether we’re at work or at home, so indoor air quality is really important for health and quality of life,” Tan added. “We’re hoping that becomes a sustainable message.”

On a drizzly weekday in late March, Jenna Truong and Daniel Hwang, both part of King County’s environmental health team, spent the afternoon organizing and distributing free portable air cleaners to local business owners from a warehouse in Kent.

For much of last year, Truong and Hwang joined other public health staffers in reaching out to thousands of King County businesses, community organizations and school districts to explain the importance of better indoor air quality and set them up with portable air cleaners for their buildings.

The outreach is part of larger county efforts to teach community members about how good indoor ventilation can not only reduce COVID spread, but also increase long-term public health.

“COVID has changed a lot in the last two years, but the principles of good ventilation and how to improve indoor air quality have not changed,” said Marissa Baker, assistant professor of environmental and occupational health sciences at the University of Washington.

Most all spaces can usually either open a window or door, use portable cleaners or bring in fresh air through a ventilation system, though that can be expensive and time-consuming, Baker said.

To date, Public Health — Seattle & King County has provided over 1,500 free evaluations of buildings and their air circulation systems and distributed nearly 2,000 HEPA filters — high-efficiency particulate air filters — to communities more at-risk of COVID spread. HEPA filters can remove 99% of dust, pollen, mold, bacteria and other airborne particles with a diameter as small as 0.3 microns, including particles that contain the coronavirus, according to the U.S. Environmental Protection Agency.

The efforts have helped many businesses facing challenges as they navigate often complex ventilation upgrades.

Outside the Kent warehouse, one local business leader, David Bestock, pulled his car into the parking lot to pick up an order of filters. Bestock, executive director of the Delridge Neighborhoods Development Association, arrived hoping to better clean the air at the organization’s Youngstown Cultural Arts Center.

“So, have you ever used one of these before?” Truong asked him, gesturing to a unit propped up on a table. After months of this work, she’s become an expert at giving a quick how-to on the machines.

In HEPA cleaners, indoor air passes through a series of filters that capture and remove pathogens before releasing clean air into a room. HVAC systems are bigger systems installed in buildings that often bring outdoor air inside, recirculate it and send it through a furnace filter before releasing it into a building.

“These filters are great year-round,” she said. “They help with wildfire smoke (and) they can help if anyone in your office has asthma or allergies, so they’re a really robust tool that isn’t just adding a layer of protection for COVID, but for other things as well.”

Bestock and his co-workers have secured a couple other HEPA cleaners as the Youngstown center slowly reopened to the public — but it’s an older building, meaning the options for good air filtration are limited, he said.

“We have HVAC units for two of our main rental spaces, but everything else is just windows and electric fans/heaters, which are on the ceiling and are terrible. … That’s why we need these,” he said.

Khadra Mohamed — who runs Saharle Daycare, a small, child care center in Kent — said she was hit with a huge wave of relief when she heard about the county’s efforts to give out the cleaners to local organizations.

“I went online weeks ago (looking for an appropriate air purifier) and it was $600,” Mohamed said after picking up two filter systems from the Kent warehouse. “I remember thinking to myself, ‘How am I going to afford this?'”

Several of her kids have bad allergies, she said, and while she tries to keep windows and doors open to bring fresh air inside, she needs a better system.

The recent push to improve ventilation systems has perhaps met the most difficult obstacles within Washington’s classrooms.

Because of old district buildings, a lack of expertise and limited funds, clean air efforts have been slow-moving, said Tyler Muench, who manages government relations for the state Office of the Superintendent of Public Instruction’s capital budget.

Refreshing air inside classrooms is among the most important measures schools can take against airborne diseases like COVID-19, in addition to distancing, masking and hand-washing, according to federal health officials and occupational safety experts.

In Washington, public schools have historically funded construction projects through the state’s School Construction Assistance Program (SCAP), which distributes funding to districts able to secure local dollars.

The formula for deciding how much funding each district gets, however, is outdated, Muench said.

“Seattle has no problem raising local revenues for construction with its healthy tax base,” Muench said. “But go out to the peninsula and you have communities where they haven’t passed a bond or levy in 20, 40, 50 years.”

As a result, communities that can’t raise local funds don’t get access to their state share, he said.

For example, the Wahkiakum School District, a rural district in Southwest Washington, is suing the state for relying on local property taxes to complete school construction, thus exacerbating equity gaps between wealthier and poorer districts, Muench said. The last seven of eight bond measures to help repair Wahkiakum’s schools have failed, KUOW reported, leaving students with inadequate science lab facilities, fire systems and earthquake preparedness plans.

For districts like Wahkiakum, environmental health experts recommend letting in as much outdoor air as possible by opening windows or doors, or upping time spent outside.

The state does offer an initiative for smaller, often more rural districts, called the Small District Modernization Program, which provides fully funded repairs to districts unable to participate in the larger construction program. But the small-district program is also underfunded, Muench said.

Because of state barriers to funding, federal pandemic relief dollars have been a “lifeline” for districts the past two years, he said.

In Seattle, public schools have cranked settings in HVAC systems to pump in 100% outside air, versus the typical setting of 30%.

Highline Public Schools in South King County bought HEPA filters for more than 100 classrooms, primarily those in older buildings without central ventilation systems. The district’s newer schools are equipped with HVAC systems.

Tacoma Public Schools is working to update its HVAC systems to reach the state’s recommended modifications, which will be funded through bonds and federal aid.

In the Lake Washington School District, each classroom gets about seven air changes per hour, which exceeds DOH’s recommendation of five to six air changes per hour. The district has also upgraded its systems to use a MERV-13 filter, which offers a high grade of filtration.

More can be done, though, particularly in parts of the state that can’t afford new ventilation systems, said Tan, the King County toxicologist.

“Investing in the HEPA air cleaners is a great way to supplement and address urgent needs during COVID,” she said, “but for a long-term sustainable change so that kids have good air in their schools, HVAC upgrades are going to be important.”

At Salem Lutheran, the sun is starting to set as the Chorale wraps up practice. The next rehearsal will be at McIntyre Hall, a performance theater down the street, in preparation for this weekend, when the Chorale will host its first in-person concert since the outbreak.

It’s a beautiful venue, members say, though that’s no longer all they look for in a performance space. McIntyre has a high-quality HVAC system, and also requires masks and proof of vaccination or a recent negative COVID test.

Homemade air cleaners aren’t a perfect solution, Chorale director Adam Burdick acknowledged, but as long as members layer protections they should be safe, Skagit Regional Health officials told the group.

“We are just so elated to be singing together again,” Chorale president Ruth Backlund said. Joy is returning even though it’s hard to shake some anxiety and sadness.

Backlund misses former members, some who were so haunted they left the Chorale, unsure if they could sing in a group again, and others who chose not to follow the vaccination requirement.

Rehearsal is over, and as members clean up and get ready to leave, they pass a stack of posters advertising the upcoming concert with a familiar springtime theme: “Celebrating in Song.”

This year, the sentiment resonates more than ever.

For tips on how to improve air quality in your home, King County public health experts give a rundown of things you can do at kingcounty.gov.

The state Department of Health also has a fact sheet on reducing COVID transmission at doh.wa.gov.

This story used information from The Seattle Times archives.