Particulates

PROFESSOR SIMON KINGHAM
The reason, in New Zealand, that we are particularly interested in particulates is because it comes out of domestic fires, and we have a lot of people heating the home with domestic wood burners. In countries where traffic is the main source of pollutants, it’s other pollutants like nitrogen dioxide, carbon monoxide and things. A particulate is a type of air pollution. A particulate is dust, in essence – it’s a solid, it’s not a gas, like you might have heard of things like nitrogen dioxide and carbon monoxide. In particulates, we talk about micrograms, so the amount of dust per cubic metre of air. Some people also like to count the number of particles – they say it’s not the size of the particles that's important, it’s the number of the particles. The particulate we are most interested in is very fine dust – it’s dust so fine, you can't see it. And so we classify it according to the size, so we have a thing called PM10, which is particulate matter less than 10 microns. So if you looked at a human hair, you get five particles of PM10 for a human hair, so you can't see it. We also talk about PM2.5, which is even smaller, PM1 , which is smaller again. There is different ways of measuring particulates – the simplest way is you draw air through a filter and you catch the particles, the dust, on filters. And what you find is that, the longer you do that on the filter, you can see the particulate because it ends up looking black. You calculate how much air you've drawn through the filter, and you weigh the filter before and after, and then you can convert that into micrograms per metre. The problem with that is that you only get an average over a fairly long period of time, so normally you have to monitor for 24 hours to get a reasonable amount of sample in New Zealand. And sometimes, what we are really interested in is how much it varies over much shorter periods of time. So we use a way of shining a beam of light through the air, and as the particles pass by that beam of light, it can measure how many particles are passing through. There is also a debate that it’s not the number, or the weight, or the volume of the particles, but it’s actually what the particles are, in a way, carrying. So there is argument that, with diesel fumes, it’s… other compounds attach themselves to the particles, and it’s the particles that take these other pollutants into your lung. So, for instance, you might hear things called aromatic hydrocarbons. The idea is that they attach themselves to the particle, and you breathe them into your lung, and maybe it’s them that's harming you.

Acknowledgments:
Sue Tyler