Why no advisory?

This morning we exceeded, for the first time this fall, the BC Air Quality Objective for a 24 hour period average (the objective is 25 ug/m3*).

Sadly, this will be the first of many times we will likely exceed this objective in the coming months.

However, it is important to note that advisories are NOT always issued when we go over the objective.

As the objective is based a rolling average of the last 24 hours, the worst period of air pollution may have already passed (in this case the worst period was four 3-4 hours after midnight last night) and there is no point calling an advisory if things are improving.

And the air is improving today (see how yellow line has dropped since last night) and it is likely to improve further as venting is good today (meaning it is easier for the smoke to disperse). However, last night’s readings mean we are over the 24 hour average and will be for a while. [UPDATE – An advisory was issued the evening of Nov. 9th but it was ended the next morning. We were over the BC 24-hour objective for at least 23 hours. We reached a high 24-hour average of 31.5 ug/m3,]

This overlay shows the relationship of our hourly readings (in yellow) to our 24-hour average readings (in blue). The horizontal line is the BC Air Quality objective for PM2.5 levels. It is only for 24-hour averages (there is no 1 hour average objective. Even though hourly readings may be well above the 25 ug/m3 mark many evenings, the day time readings bring the overall average down. But as many medical professionals state, there is no safe level of exposure to PM2.5.

When is an advisory called?

If the forecast was for an inversion (poor venting), an advisory might have been called as the smoke would have remained trapped low. The decision is up to our regional meteorologist and will factor in readings as well as venting and weather forecasts.

But even without an advisory, unless it is rather windy or very rainy, we can expect that hourly readings will again go up tonight as people add wood to their stoves. 

So don’t rely on advisories to tell you that the air is at unacceptable levels; if 24-hours of 25 ug/m3 is not good for us, you can bet that much higher hourly PM2.5 levels are also not good! Our medical health officer for the region has stated that there is no safe level of exposure to PM2.5.

How to access current and past PM2.5 readings for Courtenay

To view the air quality readings at the Courtenay station, go to the BC Government’s monitoring site for Courtenay.

You can click on the box for PM2.5  hourly readings or for the 24 hour average. When you do this, a graph of those readings will appear below.

On a computer (not a phone) you can then select the end of the graph to get a zoomed in portion below for greater detail that will look similar to the image in this post.

*ug/m3 is short for micrograms per cubic metre. (first image = 24 hour average; 2nd image is 1 hour average)

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