Before you spray air "fresheners" around your house, read this
Purdue University
When you walk through a pine forest, the crisp, fresh scent
is one of the first things you notice.
But bringing that pine scent or other aromas indoors with
the help of chemical products -- yes, air fresheners, wax melts, floor
cleaners, deodorants and others -- rapidly fills the air with nanoscale
particles that are small enough to get deep into your lungs, Purdue University
engineers have found over a series of studies.
These nanoparticles form when fragrances interact with
ozone, which enters buildings through ventilation systems, triggering chemical
transformations that create new airborne pollutants.
"A forest is a pristine environment, but if you're
using cleaning and aromatherapy products full of chemically manufactured scents
to recreate a forest in your home, you're actually creating a tremendous amount
of indoor air pollution that you shouldn't be breathing in," said Nusrat
Jung, an assistant professor in Purdue's Lyles School of Civil and Construction
Engineering.
Nanoparticles just a few nanometers in size can penetrate
deep into the respiratory system and spread to other organs. Jung and fellow
civil engineering professor Brandon Boor have been the first to study nanoscale
airborne particle formation indoors and compare it to outdoor atmospheric
processes.
"To understand how airborne particles form indoors, you
need to measure the smallest nanoparticles -- down to a single nanometer. At
this scale, we can observe the earliest stages of new particle formation, where
fragrances react with ozone to form tiny molecular clusters. These clusters
then rapidly evolve, growing and transforming in the air around us," said
Boor, Purdue's Dr. Margery E. Hoffman Associate Professor in Civil Engineering.
In a "tiny house lab" -- a dedicated residential
lab space for indoor air quality research -- Jung and Boor are using the latest
industry-developed air quality instruments to track how household products emit
chemicals that evaporate easily, called volatile chemicals, and generate the
tiniest airborne nanoparticles.
Called the Purdue zero Energy Design Guidance for Engineers
(zEDGE) lab, the tiny house has all the features of a typical home but is
equipped with sensors for closely monitoring the impact of everyday activities
on a home's air quality. Jung led the design of the lab, which was built in
2020 as the first of its kind.
With this unprecedented level of detail and accuracy, Jung
and Boor have made discoveries suggesting that many everyday household products
used indoors may not be as safe as previously assumed.
Even though it's yet to be determined how breathing in
volatile chemicals from these products impacts your health, the two have
repeatedly found that when fragrances are released indoors, they quickly react
with ozone to form nanoparticles. These newly formed nanoparticles are
particularly concerning because they can reach very high concentrations,
potentially posing risks to respiratory health.
Jung and Boor believe these findings highlight the need for
further research into indoor nanoparticle formation triggered by heavily
scented chemical products.
"Our research shows that fragranced products are not
just passive sources of pleasant scents -- they actively alter indoor air
chemistry, leading to the formation of nanoparticles at concentrations that
could have significant health implications," Jung said. "These
processes should be considered in the design and operation of buildings and
their HVAC systems to reduce our exposures."
Pleasant scents from chemical products create air
pollution inside your home
In a recently published paper, the pair found that scented
wax melts, typically advertised as nontoxic because they are flame-free,
actually pollute indoor air at least as much as candles.
Wax melts and other scented products release terpenes, the
chemical compounds responsible for their scents. Since wax melts contain a
higher concentration of fragrance oils than many candles, they emit more
terpenes into indoor air.
It's the terpenes in these products that rapidly react with
ozone, triggering significant nanoparticle formation. In fact, the nanoparticle
pollution from wax melts rivals that of candles, despite the absence of
combustion. These findings highlight the need to study noncombustion sources of
nanoscale particles, such as fragranced chemical products. Jung and Boor found
in another study that essential oil diffusers, disinfectants, air fresheners
and other scented sprays also generate a significant number of nanoscale
particles.
But it's not just scented products contributing to indoor
nanoparticle pollution: A study led by Boor found that cooking on a gas stove
also emits nanoparticles in large quantities.
Just 1 kilogram of cooking fuel emits 10 quadrillion
particles smaller than 3 nanometers, which matches or exceeds what's emitted
from cars with internal combustion engines. At that rate, you might be inhaling
10-100 times more of these sub-3 nanometer particles from cooking on a gas
stove indoors than you would from car exhaust while standing on a busy street.
Still, scented chemical products match or surpass gas stoves
and car engines in the generation of nanoparticles smaller than 3 nanometers,
called nanocluster aerosol. Between 100 billion and 10 trillion of these
particles could deposit in your respiratory system within just 20 minutes of
exposure to scented products.
Future work in the only lab of its kind
To continue learning more about chemical emissions and
nanoparticle formation indoors, Jung and Boor are working with industry
partners to test new air quality measurement instruments in Purdue's tiny house
lab before they are put on the market. Companies have been drawn to this lab
because it's a more realistic setting than chamber environments typically used
for indoor air quality research and developing new products.
"When companies see top-tier research coming out of
Purdue, they want to be part of it," Jung said. "And if they have an
innovative product, they want experts to push it to its limits."
One of those instruments is a particle size magnifier --
scanning mobility particle sizer (PSMPS) developed by GRIMM AEROSOL TECHNIK, a
DURAG GROUP company. With this cutting-edge instrument, Jung and Boor can
measure nanoparticles as small as a single nanometer as soon as they start to
form.
Having a way to collect high-resolution data on the rate of
new particle formation and growth indoors has allowed the pair to publish
breakthrough studies comparing nanoscale particle emissions between indoor and
outdoor atmospheric environments. Since indoor air quality is largely
unregulated and less studied than outdoor air, these comparisons are important
for understanding pollutant exposures and improving indoor environments.
Jung and Boor also use the tiny house lab to study how a
range of other everyday household activities could impact a home's air quality,
such as hair care routines. Jung and her students have found that several
chemicals, particularly cyclic volatile methyl siloxanes -- which are
ubiquitous in hair care products -- linger in the air in surprising amounts
during and after use. In a single hair care session at home, a person can
inhale a cumulative mass of 1-17 milligrams of these chemicals.
Toxicologists will need to build upon these studies to find
out exactly how harmful it could be to inhale complex mixtures of volatile
chemicals and nanoscale particles indoors. As their research continues, Jung
and Boor also hope their findings will improve how indoor air quality is
monitored, controlled and regulated.
"Indoor air quality is often overlooked in the design
and management of the buildings we live and work in, yet it has a direct impact
on our health every day," Boor said. "With data from the tiny house
lab, we aim to bridge that gap -- transforming fundamental research into
real-world solutions for healthier indoor environments for everyone."
Jung and Boor's air quality research is largely funded by the National Science Foundation, the U.S. Environmental Protection Agency and the Alfred P. Sloan Foundation Chemistry of Indoor Environments program.
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