How outdoor pollution affects indoor air quality

Reputation: Pixabay / CC0 Public Realm

Just when you thought you could go inside to be safe from the air pollution that threatens Salt Lake Valley, new research shows that air pollution incidents are elevated, like horrible movie bugs. , digging their way into interior spaces. The research, conducted in collaboration with the Utah Department of Construction and Resource Management, is published in Total Environmental Science.

In a longitudinal study of a building in the Salt Lake area, researchers found that the amount of incoming air pollution depends on the type of outdoor pollution. Wildfires, fireworks and winter movements all affect indoor air to varying degrees, says Daniel Mendoza, research assistant professor in the Department of Atmospheric Sciences and visiting assistant professor in the Department of City Design. -town & Metropolitan. The unique study, Mendoza says, combines a long-term indoor air quality monitoring project with a pair of outdoor measurements and research-grade instruments.

“We all know about the changes,” Mendoza says. “We all know how much of a problem wildfires are. But do we know what happens when we’re indoors?”

The situation

Mendoza, who also holds assistant professorships in the Pulmonary Department at the School of Medicine and as a senior scientist at the NEXUS Institute, and his colleagues set up their aerial survey equipment at the United States Laboratories in Taylorsville, Utah. They installed three sensors to measure air measurements of granular material: One on the roof to measure outside air, one in the air handling chamber – where the outside air enters – and one in an office. The building uses a 100% external air filtration system; this is not normal for most commercial buildings, which typically use some recirculated air.

The sensors remained in place from April 2018 to May 2019, just over a year. In the Salt Lake Valley, year-round air quality events include Independence Day holiday on Independence Day and Pioneer Day (July 24), smoke from wildfires across the West that settles in the valley like a bowl and winter movements in which the distributions of the whole valley. locked in a pool of cold air.

Throughout it all, sensors kept the watch team. Among the anticipated events, however, was a private fireworks display held on August 17, 2018, within five miles of the study building, allowing for an unexpected search. More on that later.


At a winter changeover event in December, as the Outdoor Air Quality Index reached orange and red levels, indoor air quality reached yellow levels and remained there until the inversion turned. Overall, indoor pollution levels were about 30% of those outside.

How outdoor pollution affects indoor air quality

Minute and indoor minute measurements of indoor air material during the December 2018 turnover. Reputation: University of Utah

That is not surprising, Mendoza says. In motions, only about 20% of air pollution is known as primary pollution – the granular material that comes directly from combustion fuels. The rest are secondary – formed as gases under chemical reaction under specific physiological conditions and combine to form hard grains. As soon as the air comes in, these meteorological conditions change.

“That changes the chemical environment for these grains and they separate,” Mendoza says. “That’s what we suspect happens when those grains come into the building and that’s why we don’t look at them.”


At the end of August 2018, when three active wildfires were burning in California, indoor air pollution rose to about 78% of outdoor pollution levels.

How outdoor pollution affects indoor air quality

One-minute outdoor and indoor airborne measurements at a wildfire event in August 2018. Credit: Daniel Mendoza.

“For nearly 48 hours,” the researchers wrote, “indoor air quality reached levels that were seen as a problem for health-conscious populations and almost reached levels that were dangerous for all peoples. “

It is important to note, however, that thanks to the building’s air handling system, the air is still safer indoors than outside.

The reason for higher infiltration of granular material, Mendoza says, is that mist particles are stable and do not break down in different temperature and humidity conditions.

“We see these particles travel directly through the system,” Mendoza says, “because there is no specific filter that excludes these particles. Smoke particles can be smaller. that’s why they’re so dangerous to us. “


Utah has two main fireworks holidays: July 4 and July 24 (Pioneer Day). But the researchers caught a signal from a private fireworks event just weeks before the wildfire event, giving an opportunity to see how fireworks show, both large and small, impact indoor air.

How outdoor pollution affects indoor air quality

Minute measurements of outdoor and indoor air conditioning during the Independence Day holidays 2018. Reputation: Daniel Mendoza

The smoke from fireworks is somewhere between transformational pollution and wildfires. There are key smoke particles in addition to the gases that can come together to remove secondary grains, which come from the chemicals used to make bright fireworks colors.

On the night of July 4, 2018, air quality dropped sharply as fireworks displays began and remained in the red zone, with spikes into the purple zone “very unhealthy”, for about three hours. Indoor air quality reached orange levels, recording about 30% of outdoor air pollution.

“It was only after 8 a.m. on July 5 that indoor air quality returned to pre-fire levels,” the researchers write.

The private fireworks display on August 17 lasted only 30 minutes, and although the range was much smaller, the fog was still enough to lift the indoor air quality index to orange for several minutes. .

How outdoor pollution affects indoor air quality

Minutes minutes outside and inside a quantity of indoor air material at a private fireworks event. Credit: University of Utah

“Even a ‘small’ fireworks display has had a huge impact on indoor air quality,” says Mendoza. This is important for people with respiratory challenges who are capable of major air quality incidents such as accidents and fireworks holidays. See coming – but private fireworks may show an unpleasant surprise.

The commercial building explored by the researchers is a relatively controlled environment. Learning about indoor air quality in homes will be another challenge. “You have kids coming in with mud or dirt on their feet, you empty and cook. So that’s our next step.” Because a lot of people spend more time at home due to COVID-19 pandemics, we hope the research will help understand what people can do to improve indoor air quality.

“There are many opportunities to reduce the pollutants reached by occupants of buildings, both commercial and residential,” said Sarah Boll, deputy director of Utah’s Department of Construction and Facilities Management. “For me, that’s a big part of this job – with more research it can identify a way to protect people inside.”

TRAX air quality monitoring is expanding

Further information:
Daniel Mendoza et al, Longitudinal analysis of the relationships between internal and external fine-grained pollution: A case study using research-level sensors, Total Environmental Science (2021). DOI: 10.1016 / j.scitotenv.2021.145778

Presented by the University of Utah

Citation: How Outdoor Pollution Affects Indoor Air Quality (2021, February 22) Retrieved February 22, 2021 from affects-indoor-air.html

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