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IAQ and Wildfires

How Useful are Low-Cost Air Quality Monitors Against Wildfire Smoke?

From ASHRAE Journal Newsletter: Sept. 22, 2020

As wildfires continue to threaten the west coast, hazardous air quality levels are of concern.

“We understand that in the United States, wildfire smoke is probably the single biggest air quality threat,” said Lawrence Berkeley National Laboratory Researcher Woody Delp.

Delp was one of the lead authors of a recently published study that investigated how well low-cost air quality monitors performed during actual wildfire pollution events. For the study, Delp and coauthor Brett Singer, Ph.D., Member ASHRAE, tested four low-cost air quality monitors. The researchers concluded the monitors could help consumers, engineers and building operators/managers have better tools to understand their building’s performance during a wildfire.

“It's kind of shocking that these things perform as well as they do,” said Delp.

This particular study focused on wildfire smoke, but the researchers have also been looking at how these monitors perform beyond wildfires and against other generalized sources, such as the impact of cooking on indoor air quality, said Delp.

“With adjustment factors that seem to be fairly consistent across most fires, the monitors can provide quantitative information, so the public can actually use the numbers in a pretty reliable manner,” said Delp. This is despite the fact that different types of fires (crowning or smoldering) can produce slightly different types of particles.

ASHRAE Journal staff talked with Delp and Singer to learn more about their research and how it can help increase resilience against wildfires.

1. What is the significance of this research?

Delp and Singer: this work helps consumers, engineers and building managers and operators better use tools for understanding how their buildings and surroundings are performing during an adverse event like a wildfire.

2. Why is it important to explore this topic now?

Wildfires are a reality. They are not going away and the smoke can travel hundreds of miles. A significant percent of the U.S. population is now impacted by wildfire smoke for several days to several weeks every year.

3. How could these monitors help building occupants during these current wildfires?

They can help occupants understand if the building they are in is providing enough protection. Sometimes staying inside with the windows closed may be good enough. When outdoor air quality is really bad, and especially if the building is very leaky, active filtration is often needed. These monitors can help people figure out if the filtration is sufficient or if more is needed.

In commercial buildings, monitoring can inform building managers if the changes that they have made to outdoor air supply and filtration are adequate. And the monitors can give occupants of those buildings data to assess if building level changes ae providing enough protection to their spaces.

In all of these situations, it is really helpful to have corresponding outdoor data as that defines the level of challenge for the building systems to provide protection.

4. What lessons, facts and/or guidance can an engineer working in the field take away from this research?

They can understand how to use these new inexpensive devices, what the numbers mean and, perhaps most importantly, what their indoor/outdoor (IO) ratio of particle concentration is. Knowing the IO ratio sheds insight on filter and HVAC performance.

5. What do you want people to take away from this research?

Particulate matter (PM2.5) has health concerns, but unless it is really bad, it is something we often do not think about. Accurately measuring PM2.5 is challenging, whether you spend hundreds or tens of thousands of dollars. The current crop of low-cost sensors is capable of providing information as useful as devices costing many times more. The community needs to be aware of the limitations and applications of the sensors for the devices to be truly useful.

This study focused on wildfire smoke as probably the greatest acute air quality health threat. Our study [and another recent one led by EPA researchers that appeared in the same edition of Sensors as our research] found that multiple units from each brand of monitor have consistent responses to smoke and can therefore be used to track it both outdoors and inside buildings. Responses differ somewhat for the different monitors, so a different numerical adjustment may be needed for each. We have also looked at the use of low-cost monitors for measuring PM2.5 emitted from common residential sources and found a slightly different result: each monitor provided consistent results for repeated exposures to the same source, but the responses varied by monitor and by source.

Bottom line: for wildfire and wood smoke, the monitors can provide quantitative information if multiplied be the appropriate adjustment factor tor the source. For many other sources, the adjustments vary enough that the information is only semiquantitative. That is good enough to activate controls, but not to tell us exactly how much PM exposure occurs to all the varied sources—including PM coming in from "normally polluted" outdoor air.    

6. How can this research further the industry's knowledge on this topic?

Until recently, PM measurement was too expensive to do on a building scale. This highlights that it is now cheap enough, and with care the data is useful.

7. What are the benefits of measuring on a building scale?

Measuring on a building scale provides hard data. Without measurements, making changes to filters and damper settings is prescriptive: you can predict what the outcomes should be, but you won’t know unless you measure. Filters sometimes get installed incorrectly, and economizer dampers have a reputation of not always working as intended.

8. Were there any surprises or unforeseen challenges for you when preparing this research?

That the low-cost monitors performed as well as they do was a big surprise. The challenges are working with the data streams.

9. What are the next steps for this topic regarding research?

Broadly, we need to evaluate performance of other sensors, notably including CO2, NO2 and VOC for indoor sources and conditions. How all of this information is used and interpreted depends on your objectives.

From a residential point of view, work is needed on algorithms that can identify the source of the particles. This is important because the calibration factors change from one source to another. As an example, stir frying dinner is fundamentally different than kids chasing the dog through the house.

In office buildings, the sources do not change as much, but we still have some work to do in developing methods and protocols for diagnostic use and retro-commissioning.