As a mother of two children under 4, living under polluted Beijing skies scares me. It’s a problem that isn’t going away anytime soon, no matter how hard the wind blows. That’s why I’ve spent so much time trying to understand how best to keep these two sets of little lungs safe on bad air days. I have outfitted my house with air filters and I want to get my home’s air quality assessed. But first, I learned that you must choose a company that offers to check indoor air quality based on mass concentration and not just particle count. Here’s why:
Pollution is made up of particulate matter or PM (i.e. bad stuff) that is broken down into categories based on size. PM10 means that the nasty particles in the air are 10 micrometers (µm) in diameter or less, smaller than the width of a single human hair. This used to be the global measurement norm, but recently scientists have discovered that even smaller particles, namely PM2.5 and smaller, are more dangerous and require a separate reading. So particles between the size of 2.5µm-10µm in diameter are classified PM10; particles 2.5µm or smaller are classified PM2.5.
First, because a greater number of small things fit into the measuring space – one cubic meter – there’s a huge variability issue when it comes to counting 2.5 particles. Imagine a room measuring at 200 and then someone lighting up a cigarette. The huge differential result from the smoke particles is hard to make sense of.
Secondly, since the smaller particles are all dangerous, how does a particle counter decide what size to count? Just the ones that measure 2.5µm in diameter? What about the ones that 1µm or 0.1µm? The smaller they are, the more dangerous they are, but a count doesn’t tell us what percentage of particles are extremely small versus those closer to 2.5.
So, the solution is to weigh the particles, not to count them., i.e. mass concentration. Not only does this method include the range of sizes, it doesn’t create range spikes in the readings in cases where we’re dealing with an increase of smaller (more dangerous) particles. Since the smallest ones are the lightest ones, it won’t be reflected in a numeric reading so vastly different than the previous reading. But that doesn’t mean we don’t know they’re there!
Put it this way: mass concentration is more accurate. The WHO and numerous health studies think so too. All of their figures for health and safety are based on mass concentration. So, if a company offers you a particle count, you can’t even compare that with the WHO health standards without knowing how to convert it. Basically, it’s irrelevant. So, say no thanks!
Then, read the next blog. I’m going to book a home assessment and tell you all about it.
Photos: Courtesy of maralinga and stevenzhang1221(flickr)