By Laura Matchett
Have you ever wondered what people mean by “particulate matter” or “PM” when discussing air quality and the AQHI (air quality health index)? If yes, then read on for a crash course about this important air pollutant.
What is particulate matter?
Particulate matter (abbreviated as PM) are solid particles and liquid droplets that have become airborne. They can be emitted from natural or human sources.
Examples of natural sources: wildfires, dust, pollen, sea spray, volcanoes
Examples of human sources: bonfires, vehicles, industry, heating, cooking
Particulate matter can be further classified as primary or secondary depending on their emission source. Primary particles are released directly from the source, while secondary particles are formed in the air through chemical and physical reactions. Many emission sources result in both types of particles. For example, during a fire (natural or human source), the more visible particles (soot and ash) are primary, but you also get the formation of smaller secondary particles through the reactions of gases released during this high temperature event.
Lastly, we can classify particulate matter by its size. This is arguably the most important classification as it directly relates to the health risk of the particles as explained in the next section. The two main size classifications are PM10 (particles less than 10 micrometers in diameter) and PM2.5 (particles less than 2.5 micrometres in diameter). These particles are very small and are hard to see individually as PM2.5 are ~30 times smaller than the width of a human hair or fine beach sand. However, when present in large amounts they can drastically reduce visibility. PM10 particles are often primary and, from our examples above, can include pollen, sea spray, ash from fires or volcanoes, or dust from soil, roads, or industrial activities. PM2.5 particles are more often secondary and are formed from gases emitted from vehicle exhaust, industrial activities, heating, cooking, or fires.
How is it linked to air quality?
Inhaling particulate matter has many negative consequences for human and animal health. For example, most of us have experienced firsthand some of the physical symptoms of poor air quality such trouble breathing or throat irritation during extreme events such as wildfires. Additionally, continuous exposure to particulate matter, even at lower levels, can lead to long term health problems.
For these reasons, particulate matter is one of the three air pollutants used to calculate the air quality health index (AQHI). The other two air pollutants are ozone and nitrogen dioxide. The AQHI indicates the level of risk associated with local air quality and ranges from 1 to 10+ with larger numbers corresponding to a larger risk. While all particulate matter can pose health risks, the AQHI specifically used PM2.5 because smaller particles have the potential to go deeper into your respiratory system leading to greater health problems. On the other hand, larger particles (like dust or ash) can get trapped in your nose or throat before reaching your lungs which reduces their health risk. The main point to remember is that more particulate matter means worse air quality, a larger AQHI, and a larger health risk.
How does CRAZ measure particulate matter?
To report the AQHI throughout Calgary, CRAZ measure PM2.5 at 4 permanent stations (Inglewood, Varsity, Southeast, and Airdrie) and 1 mobile station (currently in Cochrane). The measurement is accomplished using scattered light spectrometry which provides continuous real-time data. A simplified explanation of how this works is as follows. As particles enters the instrument they are hit with a beam of light, which results in a portion of the light changing direction (scattering). The extent of this scattering can be used to calculate the size and mass of the particles present. Thus, we obtain data giving us the concentration of particles present at any given time, which is then used to calculate the AQHI.
How can you limit your exposure?
When we think of times of high particulate matter pollution our mind often goes to extreme events such as wildfire smoke. However, in the day-to-day of a city, exposure to particulate matter results primarily from the emissions of vehicles, fuel burning, industrial activities, and other human sources. Thus, it is important to regularly check the AQHI in your area and make appropriate decisions to protect your health. Keep in mind any pre-existing conditions (like asthma) that you or your loved ones may have that can aggravate the effects of particulate matter exposure at lower AQHI levels. Below are some tips you can use to limit your exposure in your everyday activities.
- Wear a mask or stay indoors on days where the AQHI is high.
- Wear a mask when performing tasks that generate high amounts of localized particulate matter (g., cutting wood, working around vehicles exhaust).
- Where possible apply dust suppressants or collect dust at the source.
- Reduce vehicle use by taking transit, walking, or biking.
- When you need to drive, avoid idling your vehicle.
- Avoid gas-powered lawn, garden, and other tools.
- Reduce your use of backyard bonfires and indoor fireplaces. Try to keep the fires small and short when you do use them.
- Ensure your home is equipped with good ventilation and proper air filters (rated MERV-13 or higher). Change these filters out regularly.
While the AQHI tells us about the outdoor air quality, it is important to remember that there are many sources of particulate matter inside buildings (e.g., cooking, heating, cleaning) that can decrease air quality. If you want to learn more about indoor air stay tuned for our next blog post examining this topic including ways to improve your indoor air quality.
