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Taking Measure

Just a Standard Blog

Indoor Air Quality Is Nothing To Sneeze At

finger pointing to dirty air filter
Credit: ©napatcha/

Have you ever wondered if the things inside your house that you consider safe and harmless actually are? The perfume that you spray, the plastic food containers that you put in your dishwasher, the carpet that your kids lie on as they watch their favorite TV show, even the wrinkle-resistant clothing you wear—all of them could be potential sources of indoor air pollution.

We don’t normally think about stuff inside our homes emitting pollutants, but just about all building materials and consumer products emit organic compounds. When I say “organic compounds” I don’t mean expensive broccoli, though broccoli and all foods are made of organic compounds. No, when I say “organic compounds,” I mean molecules that contain or are based on carbon.

For example, you may have heard of hydrocarbons like crude oil, the stuff we make gasoline, plastics and all kinds of other things from. Hydrocarbons are organic compounds, and like several other organic compounds they can be volatile, meaning they can release vapors or gases. Volatile organic compounds can also react with ozone and other molecules in the air to form compounds that can condense into airborne particles or attach onto particles already present in the air inside your house.

Now consider that Americans spend almost nine times as much time indoors as they do outdoors.

Nine times!

Outdoor particles and gaseous pollutants enter a building through cracks and leaks in the exterior envelope. Indoor chemical reactions generate particles as well. (As you can see, my group spends the bulk of our funding on research, not graphics.) 

This means that if a pollutant is present indoors at the same concentration as outdoors, your exposure to the pollutant is about nine times higher indoors. It turns out that while some pollutants occur at higher concentrations outdoors, there are many others that actually have higher concentrations indoors. These pollutants may be emitted from indoor sources and may linger inside buildings. This can make our indoor exposure to these pollutants 10 to 1,000 times higher than our outdoor exposure.

One of the things that people have been doing to make their homes and other buildings more energy efficient is to make them more airtight. While it’s a great idea to keep cool air in during the summer and warm air in during the winter, unless you have a ventilation system that brings in enough outside air you’re also trapping in pollutants. At the same time, we’re bringing in more synthetic products, many of which are formulated with materials that emit volatile organic compounds. Synthetic carpets, for instance, have these compounds in them and may also be pre-treated with stain protectors, fire retardants and insecticides that also contain them.

Could our exposure to indoor pollutants be contributing to the seemingly upward trend in asthma (PDF), allergies (PDF), and respiratory and mutagen-related diseases?

Here I am preparing a slurry of the particles I collected from the Indoor Air Quality and Ventilation Group’s test house. I use this slurry to measure the oxidative potential of particles with an EPR spectrometer. 

With my training in environmental and biomedical engineering, I wanted to know if there were environmental factors that contribute to oxidative stress in the body. Oxidative stress indicates an imbalance between the reactive oxygen species, which include free radicals, produced by the body during metabolism and the protective antioxidants that counteract their effects.

(Free radicals may be bad for your health because they steal electrons from the atoms that make up your cells, which may disrupt cellular function and lead to cellular and DNA damage.)

During my doctoral research I measured the concentration of reactive oxygen species on airborne particles in different indoor and outdoor environments. I found that the indoor concentrations of reactive oxygen species on airborne particles were similar to the outdoor concentrations. When I increased the indoor concentrations of volatile organic compounds and ozone in my experiments, I found that the concentration of reactive oxygen species on the airborne particles increased. This result clearly showed that we can influence the quality of the air we breathe indoors based on what we choose to bring inside.

A year and a half ago I was awarded a NRC RAP fellowship to study the oxidative potential of airborne particles. The oxidative potential of particles is their ability to oxidize things or steal electrons. This is another way of quantifying the possibility that particles can cause harm to the human body after they are inhaled.

The Indoor Air Quality and Ventilation group's test house, my home away from home. 

I have been conducting a series of tests at the Indoor Air Quality and Ventilation Group’s test house to study the factors that influence the oxidative potential of airborne particles. For my experiments, I use something like a vacuum cleaner to collect airborne particles onto special bottle cap-sized filters. Then I make a slurry of the collected particles and measure their oxidative potential using the NIST Polymeric Materials Group’s electron paramagnetic resonance (EPR) spectrometer.

Since I am dealing with particle masses of less than 0.1 milligram at times, I asked the NIST Mass and Force Group for help in weighing the particles.

These measurements that my colleagues are helping me with let me calculate the oxidative potential of particles based on their mass; information that is important when modeling the movement and chemistry of these pollutants.

I have also worked with my group to measure the concentrations of another volatile organic compound, formaldehyde, in NIST’s Net-Zero Energy Residential Test Facility. Formaldehyde, which is normally associated with embalming fluids and dissections in high school biology classes, is also used widely in pressed-wood products, glues, wrinkle-free clothing, and some insulation materials. Even though the Net-Zero Energy house was built with materials that did not contain any added formaldehyde, we were able to detect this carcinogenic compound (PDF) at levels that indicate it is being emitted from materials in the house (natural wood emits formaldehyde) and may also be forming from chemical reactions taking place in the air or on surfaces inside the house.

The fluctuations in the measured real-time formaldehyde concentrations matched predicted concentration trends (PDF) from CONTAM, a computer program developed by my group to predict airflows and pollutant concentrations in residential and commercial buildings.

Me at the helm of the electron paramagnetic resonance spectrometer.

The knowledge I have gained about indoor air quality has made me into a more cautious person. I used to burn scented candles at home occasionally without giving it much thought, but studies (PDF) have shown that the sweet-smelling compounds emitted from scented candles are actually very reactive with ozone and radical species present in the air. These reactions generate microscopic particles in addition to the soot emitted from burning candles.

While I haven’t thrown away my scented candles, I burn them quite rarely now (usually only on hot summer or cold winter days after I’ve been cooking, but when I don’t want to open the windows to get the “smell” out). And I try to open my windows to ventilate as often as I can.

That said, convenience is important in today’s busy lifestyle, and we all have to make our own decisions. It’s the job of scientists such as myself to communicate the results of our research to manufacturers, regulators and other stakeholders so that the potential risks associated with these modern conveniences can be assessed and minimized.

After all, my family is exposed to these compounds, too. It makes me feel good to know that the work I do can contribute positively to my, and your, families’ health.

About the author

Shahana Khurshid

Shahana Khurshid is an NRC RAP fellow in the Indoor Air Quality and Ventilation group at NIST. She received her B.S. in Environmental Engineering from MIT, M.S. in Biomedical Engineering and Ph.D. in Environmental Engineering from the University of Texas at Austin. She was an avid cat lover growing up in Karachi, Pakistan, and now enjoys watching her children ‘kitten’ around with each other.

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It may be of use to give us a calculation on just how much it costs to heat / cool some quantity of air exchange in our homes. My lunch-bag calculation says it is inexpensive to heat 100 Cu-Ft of air/ minute entering a house. The energy loss/gain in the average house is a lot more due to temperature differences and home insulation, not sole air leakage. I think it is very bad for our health to seal up a home and only saves a few dollars per month. How about NIST doing the calculation at 100 CFM, "24X7", and average Natural Gas costs? Thanks
Charles, Having a well-ventilated home is the answer, not necessarily having a leaky home. A home with leaks in its exterior may bring in a lot of outdoor air on a windy day, but not much at all on a calm day. And the energy costs associated with infiltration of air into leaky buildings is not trivial – it amounts to 13% of total energy use in the residential sector, according to a 2014 DOE report. The expert opinion is to build a tight building and bring in a steady flow of outdoor air through a ventilation system. Energy costs for heating and cooling a house vary based on the regional climate, the efficiency of the HVAC system, the building envelope, etc. At NIST’s net-zero energy residential test facility (which is a very energy-efficient house), conditioning 100 cfm would cost 15% of the ~14,000 kWh consumed at the house annually. At a more typical house in Maryland, conditioning 100 cfm will likely consume more energy than this. But the costs associated with ventilation are well worth it, in my opinion, considering that ventilation reduces the concentration of pollutants emitted from indoor sources. So the answer is not really to encourage the use of leaky buildings, rather to develop well-ventilated buildings.
Great info! Definitely will take this into consideration when looking for the right air filter. Thank you!

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