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Lessons Learned From Smoke Season 2023 About Protecting Indoor Air Quality

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Jay Stein's picture
Senior Fellow Emeritus, E Source

Jay Stein, a Senior Fellow Emeritus affiliated with E Source, is one of America's leading energy technologists. Over the course of his over 40-year career he has played numerous roles, including...

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  • Sep 18, 2023

The 2023 wildfire season was an eye opener for many people, albeit a bloodshot one. Usually, it’s only the Western US that has to deal with wildfire smoke, but this year, smoke from Canadian forest fires poured down into eastern states, some over a thousand miles away. Many people sought refuge in buildings, where unbeknownst to them, the operators of those buildings faced a dilemma.

While at the time, building air may have been cleaner than outdoor air, indoor air is rarely pristine. It often contains carbon dioxide (exhaled by occupants), pathogens like viruses (also exhaled), volatile organic compounds (outgassed from furniture and carpets), and particulates (microscopic particles from burning fuel in gas stoves and fireplaces). Plus, whatever pollutants are outdoors find their way indoors. In homes we often mitigate these contaminants by opening windows, but commercial buildings—like offices, schools, and stores—are equipped with ventilation systems that automatically bring in outdoor air to dilute contaminants. That works fine when the outdoor air is clean, but what are building operators to do when the outdoor air is filled with smoke?

I spent a good deal of time this summer ruminating on this question and found that it begs a much bigger one. Of course, it makes sense to avoid breathing wildfire smoke. It contains particulates (abbreviated as PM2.5 in air quality apps and web sites) that are so tiny they penetrate deep into our lungs. Particulate pollution has been linked to numerous disorders, including asthma and cardiovascular disease.

But wildfire smoke isn’t the only outdoor air pollutant we need be concerned about. In some ways, other air pollutants are more insidious. Most are gasses, and many are odorless and colorless. We don’t immediately feel the irritation they’re causing, so they don’t get the same level of attention as wildfire smoke. Gaseous air pollutants include ozone, volatile organic compounds, and nitrogen oxides, and they also have the potential to damage both our respiratory and cardiovascular systems. Ozone is especially dangerous. According to the American Lung Association, “exposure to unhealthy levels of ozone air pollution makes breathing difficult for more Americans all across the country than any other single pollutant.”

Overall, the concentrations of virtually all US outdoor air pollutants dropped over the last few decades, but that progress isn’t uniform across the country. There are still plenty of places that all too frequently experience poor air quality. According to the American Lung Association, nearly 120 million Americans “live in places with failing grades for unhealthy levels of ozone or particle pollution.” Building operators in these high pollution areas can’t count on having a consistent supply of clean outdoor air.

What are these building operators to do? For one thing, they can install high-efficiency filters to remove both particulates and pathogens, like viruses. For another, they can install special filters designed to remove gaseous contaminants, like carbon dioxide and ozone, directly from indoor air. Air cleaned by a combination of high-efficiency filters, and special gas-removing filters, is often cleaner than outdoor air.

Building operators using such filter combinations don’t have to rely on having clean outdoor air to dilute indoor contaminants and can dramatically reduce their outdoor air intake. They also avoid the energy consumption associated with heating outdoor air up and cooling it down to room temperature. Not only do those energy savings help pay for such advanced filters, but they also reduce the extent to which buildings contribute to climate change. Which brings us full circle, as it’s climate change that’s now exacerbating our outdoor and indoor air pollution problems.

Smoke gets in your eyes

The most dangerous component of wildfire smoke is particulates, but wildfires are not the only source of particulate pollution. Others include factories, power plants, and gasoline and diesel motors. Particulates have been linked to cardiovascular disease, including heart attacks, strokes, chronic obstructive pulmonary disease, and asthma. According to the American Lung Association, they are responsible for nearly 48,000 premature US deaths annually. Some of the worst metropolitan areas for particulate pollution in the US include Los Angeles and Long Beach, Fairbanks, Phoenix and Mesa, and Detroit, Warren, and Ann Arbor.

Particulate pollution also finds its way into buildings, by seeping in through cracks and open windows, and being drawn in via fresh air intakes, but outdoor air is not the sole source of indoor particulates. Internal sources include cooking (heated food puts out particulates, and if you’re cooking on a gas stove, there’s also the combustion gasses), fireplaces, burning candles, and dust.

Of all the forms of indoor air contamination, particulates are the easiest to remediate. They can be removed from indoor air using high-efficiency filters, but few buildings are outfitted with such filters.

Lost in the ozone

Ozone is a gas molecule containing 3 oxygen atoms. It forms in the lower atmosphere when volatile organic compounds and nitrogen oxides mix, and are exposed to heat and sunlight. Volatile organic compounds typically come from burning fossil fuels, such as gasoline, diesel, and natural gas, and when fuels and solvents evaporate. Major nitrogen oxides emitters include cars, trucks, furnaces, and boilers. Wildfires also increase ozone levels.

The presence of ozone in the upper atmosphere is a good thing, as it absorbs ultraviolet rays. But here in the lower atmosphere, where we all live, it reacts with the linings of our lungs and airways, causing inflammation and respiratory system damage. Ozone is linked to asthma and chronic obstructive pulmonary disease. Children and the elderly are most susceptible. Some of the worst metropolitan areas, according to the American Lung Association, include: Los Angeles and Long Beach, Phoenix and Mesa, Denver and Aurora, Houston and The Woodlands, and New York and Newark.

Just like particulates, outdoor ozone penetrates into buildings. It’s also emitted indoors by printers, photocopiers, and some air purifiers. Fortunately, ozone reacts with interior surfaces, like walls and furniture, and breaks down, so indoor ozone levels are often about one-quarter of outdoor levels. Even at those reduced levels, because we spend more time indoors than outdoors, many people inhale potentially detrimental amounts of indoor ozone.

Climate change is making things worse

For decades after the EPA issued regulations authorized by the Clean Air Act, both particulate and ozone concentrations declined. In recent years, progress on both of those pollutants seems to have stalled out, probably due to climate change.

In the case of particulates, climate change is driving up temperatures, which drys out vegetation, leading to more wildfires. The number of days in which particulate pollution hit unhealthy levels in numerous US counties started rising dramatically about a decade ago, with many scientists warning the worst is yet to come.

The story is similar for ozone. In the West, climate change is driving hotter, dryer, sunnier summers, with more frequent stagnant air conditions. These are exactly the conditions that exacerbate ozone formation. According to the American Lung Association, “climate change is undercutting the progress we would have made” on ozone. Both particulates and ozone will continue to increasingly threaten our health, both outdoors and indoors, for the foreseeable future.

Filtration first

The first thing building operators can do is to install high-efficiency filters to remove particulates. Filter manufacturers express the effectiveness of their products using the Minimum Efficiency Reporting Value scale, which ranges from 1 to 20. The higher the MERV rating, the more effective a filter is at removing a wide range of particles from an airstream.

According to the US EPA, “upgrading to a filter rated MERV 13 or higher can be especially important during smoky periods to effectively remove fine particle pollution from smoke in the indoor air.” Most HVAC system filters feature MERV ratings from 6-8, which can remove some smoke-related particles, but probably not enough to effectively protect respiratory health.

Ozone, and other gaseous contaminants, can’t be removed from indoor air using ordinary filters. In theory, they can be removed using air filters infused with activated carbon. However, those filters are expensive and they require frequent replacement. Accordingly, they’re rarely used.

How to manage indoor air quality without using outdoor air

Once high MERV filtration is in place, building operators in places with high levels of ozone pollution may want to take the next step, and clean their indoor air without bringing in much outdoor air. The technology that makes this strategy possible is known as sorbent filtration. Sorbents are materials that gas molecules naturally adhere to on contact, and can be incorporated into filters formulated to absorb carbon dioxide, formaldehyde, and ozone. When sorbent filters are saturated, such that they can no longer absorb any more gas molecules, they are regenerated by forcing hot air through them. The absorbed gas molecules are then released from the sorbent filters and expelled outdoors.

While sorbents have been used for decades in spacecraft and submarines, currently, there’s just one manufacturer of such filters for buildings: enVerid, a young company based near Boston. It not only makes the filters but also incorporates them into modules containing fans, particulate filters, regeneration heaters, controls, and dampers (see picture below). Buildings that install these modules could potentially eliminate nearly their entire outdoor air intake and the pollution that comes with it.


Courtesy: enVerid
Courtesy: enVerid

Another problem with bringing in outdoor air is that it takes a lot of energy to warm it up to room temperature in the winter, and cool it down in the summer. Reducing the amount of air brought in avoids much of that energy consumption.

The National Renewable Energy Laboratory, a US Department of Energy lab that specializes, in part, in building energy efficiency, monitored three enVerid module installations: a wellness center and two office buildings. The NREL researchers found that the sorbent filters enabled building operators to reduce outdoor air intake quantities, reduce energy consumption, and meet or exceed their indoor air quality goals. How much energy individual buildings saved depended on numerous factors, including how their HVAC systems were functioning, and the local climate. In a Miami wellness center they determined that the enVerid modules reduced cooling energy by 37% during a 3-month test period.

In new construction, sorbent filters might add little or no cost to a project. Since they reduce heating and cooling loads, the cost of the heating and cooling equipment they displace is often similar to the cost of the modules. In existing buildings, the economics are more complicated. It’s possible that the sorbent filters could pay for themselves in 10 years, based on energy savings alone. In buildings where the occupants are sensitive to ozone and other air contaminants, the health benefits could exceed the sorbent filter costs in much less time.

Here’s what you can do

If you’re interested in protecting the air in buildings, you’ve got different opportunities depending on who you are. If you’re designing a new building in an area with high levels of ozone and particulate pollution, your opportunity is clear. By specifying a combination of MERV 13, or higher, and sorbent air filters, you may be able to produce a building that better protects the health of its occupants and consumes less energy than a typical building, at little to no additional upfront cost. How can you tell if your buildings is in a high-pollution area? Check the American Lung Association’s annual State of the Air Report. It contains data for high ozone and particle pollution days for nearly every county in the US.

If you’re an operator of an existing building, or a commercial building occupant, you can figure out whether you need upgraded air cleaning systems by monitoring indoor air quality with handheld or portable monitors. For example, the Awair Element monitors carbon dioxide, volatile organic compounds, and particulates, and is available online for $209. For policy wonks, you can advocate for national and local governments to adopt indoor air quality standards for commercial buildings.

For the rest of us, who want to be able to seal up our homes on high ozone days and still breathe easily, you may be wondering when a sorbent filtration system will be available for residences. I posed this question to Christian Weeks, enVerid’s CEO, and he told me such a product is technically feasible, and his company is working on it. If the market for a premium residential indoor air quality product develops, he told me, it might be available in just a few years.

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