Material Off Gassing – The How and the Why

January 27, 2019 hiadmin

By Dr. Alice Delia —

We’re surrounded by so many things it’s easy to lose track of the everyday hazards these items can pose. For example, I love the smell of freshly cut grass – it reminds me of my childhood home and makes me feel at ease (which bring up the topic of smells and how they are perceived, but that’s a story for another time). And that’s just one of a thousand things we’re exposed to every day. Whether good, bad, or indifferent, we’re enveloped by things that contribute to what we breath every minute of the day.

Have you ever thought about how the air actually works? There are the fundamental components of nitrogen and oxygen, plus some argon, that make up 99.9% of what we breath but what about the other 0.1%? That sounds like a really small amount but it’s where all the trouble lies. Leaving aside things like carbon dioxide and water vapor, what we breath in is the result of what’s emitted around us. Most materials emit various chemicals, some relatively benign and others more hazardous like formaldehyde.

So, how does this process work? It’s generally referred to as off-gassing and it occurs all around us. It follows the general rule of balance, or equilibrium. When there’s more of something in one place than an adjacent place there’s a movement of that parameter, whether water, temperature, or chemical amount, from the higher to the lower amount until they are even. In more scientific terms, off-gassing is the “release of a gas that was dissolved, trapped, frozen or absorbed in some material” (Wikipedia).

To illustrate this concept, let’s think about formaldehyde being emitted from a wood product like particleboard. The material contains large amounts of formaldehyde in comparison with the surrounding air, so, to balance itself formaldehyde is emitted from the material into the air. The amount and rate are dependent on the amount in the material itself, the temperature, and the humidity as well as the number of air changes in that space.

But shouldn’t this balancing process happen pretty quickly? Why can we still have elevated amounts of formaldehyde a year later? This has to do with the other part of the off-gassing process – the part that occurs within the material itself. You see, it’s not just with the air that this balancing happens, it’s within the material itself as well. As formaldehyde leaves the surface to go into the air, more formaldehyde migrates from the area beneath the surface to the surface level. Where it’s also released into the surrounding air. And then additional formaldehyde migrates through the material to balance what was removed through migration and so on. Since the surface layer formaldehyde is replaced by formaldehyde from deeper within the material, there’s always some emission from that surface. As time goes on these concentration gradients get smaller and less formaldehyde is emitted until eventually a steady state is achieved.

Now remember, this process happens with all materials so the amount in the air is an aggregate of all these sources, as well as the effect of temperature, humidity, air changes, etc. So, it’s possible to have high emitting sources and relatively low concentration in the air and vice versa, low emitting sources and high concentration in the air. High temperature and humidity will always increase the amount in the air and a larger number of air changes will always decrease the amount in the air (assuming no other changes).

With this process being repeated again and again around us, is it a surprise that indoor air can be so much more polluted than outdoor air?

This article was published in the December 2018 issue of Healthy Indoors Magazine.

The post Material Off Gassing – The How and the Why appeared first on Healthy Indoors.

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