4o years ago an article published in The New York Times highlighted the threat of indoor air pollution: “The air you breathe in your home or office may be hazardous to your health – more dangerous, in fact, than the outdoor air in the most polluted of cities. This is especially so during the cold months, when windows and doors are kept tightly shut and homes, schools and office buildings are made as airtight as possible to conserve energy.”
While at the time awareness of the problem was still limited, we now know—on the basis of scientific evidence— that the air within homes and other buildings can be polluted even more than outdoor air. More and more research highlights the dangers posed by indoor air pollution.
The Environmental Protection Agency (EPA) tells us: “While pollutant levels from individual sources may not pose a significant health risk by themselves, most homes have more than one source that contributes to indoor air pollution. There can be a serious risk from the cumulative effects of these sources.”
Indoor air pollution comes from many different activities. For example, fine particles are released from cooking (frying and roasting in particular) and cleaning. Air fresheners and candles contain phthalates, ubiquitous pollutants that may cause allergic diseases in children even when exposure occurs during prenatal life.
“You are more exposed to PM2.5 (tiny particles that are hazardous to human health when inhaled) cooking an omelette in your kitchen than standing on an average London roadside, one study has found. Another study found that cooking a Sunday roast or Thanksgiving dinner could produce higher levels of PM2.5s than are found on the streets of Delhi, one of the most polluted cities in the world.”
However, air pollution within homes may also come from the external environment. Indeed, outdoor air pollution influences indoor air quality. A recently published study (February 22, 2021) shows that wildfires, fireworks and wintertime inversions all affect indoor air quality.
What are inversions? Inversions occur during the winter months when normal atmospheric conditions (cool air above, warm air below) become inverted. Inversions trap a dense layer of cold air under a layer of warm air. The warm layer acts much like a lid, trapping pollutants in the cold air near the valley floor.
Lead study author Daniel Mendoza said that the study is unique, as it combines a long-term indoor air quality monitoring project with paired outdoor measurements and research-grade instruments. “We all know about the inversions,” Mendoza says. “We all know how large of a problem wildfires are. But do we really know what happens when we’re inside?”
The researchers measured fine particulate matter for a year—using sensors located on the rooftop, air handling room, and indoor office space in a building—to assess the impacts of inversions, wildfires, and fireworks, events known to create high levels of pollution.
They found that inversions, wildfires, and fireworks had different magnitudes and durations. The infiltration rates—a measure of how fast pollutants enter a home or building— varied for each event leading to dissimilar indoor air pollution levels.
For about 48 hours after a wildfire, indoor air quality reached levels considered problematic for health compromised populations, and nearly reached levels considered unsafe for all populations. The researchers also found that even a ‘small’ fireworks show had a marked impact on indoor air quality
Sarah Boll, senior study author, said: “There is a lot of opportunity to reduce the pollutants that reach occupants in buildings, both commercial and residential. To me, that is the great part of this work—with more research it can point the way to protecting people indoors.”
The take home message is that it is necessary to consider outdoor air pollution when evaluating indoor air quality, as infiltration of contaminants is strongly dependent on the specific source of pollution.