Low-cost home air quality monitors prove useful for wildfire smoke
Berkeley Lab air quality scientists assess the performance of four
consumer devices

Date:
August 18, 2020
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
A new study by air quality scientists tested four models of
low-cost air quality monitors during actual wildfire pollution
events and found that their readings of PM2.5 - or particulate
matter under 2.5 microns, which has been linked to respiratory
and cardiovascular issues - were consistently higher than the
reference monitor used by the regulatory agencies; however, since
each monitor had a relatively consistent response to the smoke,
it is possible to use the readings to estimate true PM2.5 levels.



FULL STORY ==========================================================================
Over the last few years of frequent and intense wildfire seasons, many
parts of the U.S. have experienced hazardous air quality for days on
end. At the same time a number of low-cost air quality monitors have
come on the market, allowing consumers to check the pollutant levels
in their own homes and neighborhoods. So, air quality scientists at
Lawrence Berkeley National Laboratory (Berkeley Lab) wanted to know:
are these low-cost monitors any good?

==========================================================================
The answer is: yes -- to a degree.

Published recently in the journal Sensors, their study tested four models
of low-cost air quality monitors during actual wildfire pollution events
and found that their readings of PM2.5 -- or particulate matter under
2.5 microns, which has been linked to respiratory and cardiovascular
issues -- were consistently higher than the reference monitor used by
the regulatory agencies; however, since each monitor had a relatively consistent response to the smoke, it is possible to use the readings to estimate true PM2.5 levels. Overall, the researchers concluded that the monitors can provide actionable information.

"We compared the low-cost monitors to one that is used by regulatory
agencies in air monitoring stations. It turns out their correlations are phenomenally good. When one goes up, the other goes up at the same time,
and it is proportional. That gives us a lot of hope for being able to use
them for real information," said Woody Delp, one of the lead authors of
the study. "And it could let someone know how well their new portable
air filter is reducing smoke particles. But from an absolute point of
view, it's becoming clear these sensors require some adjustments and
checks to use the numbers." For the study, titled "Wildfire Smoke
Adjustment Factors for Low-Cost and Professional PM2.5 Monitors with
Optical Sensors," Delp and co-author Brett Singer tested four low-cost
air quality monitors:
* IQAir AirVisual Pro * PurpleAir Indoor * Air Quality Egg * eLichens
Indoor Air Quality Pro station
These devices, which cost in the range of a few hundred dollars,
were compared to reference monitors used by regulatory agencies and researchers, which cost $20,000 or more. They also tested two monitors
that are used by researchers and industrial hygienists and cost in
the range of $5,000 to $10,000. Additionally, the researchers compared
public data from PurpleAir PA-II monitors to nearby regulatory monitoring stations impacted by four wildfires in 2018.



========================================================================== Calibrations and adjustment factors In the past, air quality monitoring
has been limited to the high-priced professional monitors, making them inaccessible for personal use. The manufacturers recommend that the
devices be calibrated to the specific pollution source of interest because
the sensors use an optical sensing technique that responds differently
to different sources. Pollution from a backyard barbecue or car exhaust
may differ in size and density from pollution from a forest fire, and
a forest fire may emit different types of particles than an urban fire.

The low-cost monitors use the same optical sensing technique -- estimating particle concentrations based on light scattering -- but use mass-produced optical sensors that are not as precisely machined as those in the professional-grade devices. In contrast, the most expensive monitors,
those used by regulatory agencies, are calibrated using gravimetric
analysis, which is based on the weight of particles.

With the air quality monitors deployed at Berkeley Lab inside a
well-ventilated single-story laboratory building, the researchers
collected data as the Camp Fire burned in Northern California in the
fall of 2018. They found that the four low-cost monitors substantially overreported PM2.5 levels, by factors of 1.6 to 2.4 times higher than
the readings on the regulatory reference monitor.

However, the relative changes correlated well with both the regulatory
and professional monitors.

The researchers calculated an adjustment factor of approximately 0.48
when using PurpleAir PA-II monitors outdoors during the Camp, Carr, and Mendocino Complex Fires in California and the Pole Creek Fire in Utah
(meaning the readings should be multiplied by 0.48 to estimate the true
PM2.5 level). This correction is very close to one of the data conversion options ("LRAPA") given on the PurpleAir website.



==========================================================================
Good for other indoor pollutants too In a separate study earlier this
year, Delp and Singer, along with first author Zhiqiang Wang, evaluated
six low-cost air quality monitors by comparing their output to reference
PM2.5 and PM10 measurements from 21 common residential sources, such as
frying, grilling, microwaving popcorn, vacuuming, and burning candles. The study, published in the journal Building and Environment, was an update
to their 2018 study.

They found that for most pollution sources, the low-cost monitors tracked
with the professional ones within a factor of two for PM2.5. Delp said
the consumer monitors "enable people to identify activities that emit
fine particulate matter inside their homes and to determine if operating filters or just keeping windows closed is effectively reducing exposure
inside when there is very bad air pollution outside. For these purposes,
they work as well as professional grade monitors, and appear to be
very reliable." "We are impressed and excited by the usefulness and performance of these air quality monitors that cost under $300," said
Singer, head of the Indoor Environment Group in Berkeley Lab's Energy Technologies Area.

Both studies were supported by the Department of Energy's Building
Technologies Office and the U.S. Environmental Protection Agency Indoor Environments Division.


========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. William W. Delp, Brett C. Singer. Wildfire Smoke Adjustment
Factors for
Low-Cost and Professional PM2.5 Monitors with Optical
Sensors. Sensors, 2020; 20 (13): 3683 DOI: 10.3390/s20133683 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200818094009.htm

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