I think it's time to write an explainer about air quality ratings and what they actually mean!
This will detail:
1. Particulate counts
2. US Air Quality Index (AQI)
3. Canada's Air Quality Health Index (AQHI)
4. What this actually means for our health
🧵
1. Particulate counts
PM2.5 refers to tiny particles equal to or less than 2 microns (μm) in diameter. These are very tiny particles that are so small that they can get stuck deep in your lungs. Measuring the amount in a space can be shown in µg/m³ or ppm.
2. US AQI
The US AQI takes the measurements of Ozone, particulate matter (PM) , carbon monoxide (CO), nitrogen dioxide (NO2) and sulfur dioxide (SO2) to come up with a 0-500 rating representing overall air quality. They are grouped into 6 categories to make general statements.
3. Canada's AQHI is a calculation based on the observed relationship of nitrogen dioxide (NO2), ground-level ozone (O3) and fine particulate matter (PM2.5) with mortality from an analysis of several Canadian cities resulting in a 1-10+ rating scale. The groupings are shown here.
The AQI and AQHI are intended to indicate the exposure risk in the moment from all the air contaminants present. Limitations: these indexes are calculated using past data so lag behind current conditions. They also don't account for cumulative exposure and the scales max out
Knowing your actual exposure level is important for gauging the long-term effects of air pollution. The @WHO revised its exposure recommendations in 2021, stating, "Air pollution is one of the greatest environmental risk to health." who.int/news-room/fact…
Going back to the measurement in the quoted tweet, I measured 470.1 µg/m³ and the index ratings at the same ranged from:
US AQI: 339-480 (h/t @SafetyinNumbrz)
Canadian AQHI: 16-25 (out of 10 🫠) (h/t @stormwx1)
On the low end, 24hrs of exposure at this level is like smoking nearly 16 cigarettes. And honestly, I think that may be the most effective way to express this kind of risk, given the general public knows that cigarettes have short- and long-term harms. jasminedevv.github.io/AQI2cigarettes/
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