I live adjacent to the Whitemud, and late one evening I woke-up to an odd absence of sound. My bedroom window was open to let in some night air, and gazing out onto the Whitemud, I saw that there were no cars on the highway. Having lived in this house, with this view of the Whitemud, for 10 years this was the first time that I saw an empty highway. COVID-19 was in full effect, and people were clearly staying at home.
We’ve all seen the images of the dramatic reductions in air pollution brought on by social distancing and movement restriction policies resulting from COVID-19 in other parts of the world. Here is a great NASA data visualization for the Eastern Seaboard. Here is another of China and Korea. The Eastern Seaboard map compares the monthly average of March from 2015-2019 with March 2020, and demonstrated a 30% drop in atmospheric NO2 . The China and Korea map compared January 1-20, 2020 with February 10-25 2020, and also showed a significant drop in NO2 . The article does not specify how big the drop is.
A couple of notes on these maps:
(a) According to the USEPA, NO2
“… primarily gets in the air from the burning of fuel. NO2 forms from emissions from cars, trucks and buses, power plants, and off-road equipment.”
(b) The NO2 shown on these maps was measured using a satellite-based remote sensing tool that detects atmospheric NO2 . This is different from the collection method used for the Edmonton data (see below), which was measured using a ground-based regulatory ambient air quality continuous monitor. The specific readings are not comparable between the satellite data and the air quality monitor.
(c) As Figure 1 indicates, NO2 cycles annually. This is important because there may have been a drop in NO2 in the S.E. Asian example from January to February due to this cycle. The data does not distinguish between what portion of the drop is due to annual cycles, and what is due to factors related to COVID-19.
(d) Both the American Eastern Seaboard and S.E. Asian maps represent areas that are much more densely populated than Northern Alberta, with many more emissions sources. As such, the relative change in NO2 levels will be much greater in both these examples, as compared to Edmonton.
Now, on to Edmonton!
I’m not the only one to experience a ‘traffic moment’ in Edmonton. Many of my friends have commented on how easy it is to drive places given the lack of traffic. There has been no discernible rush hour. Bike shops are open and considered essential. So essential, in fact, that I had a hard time finding a new bike for my daughter – I was told that bikes were being sold before they even made it to the store. And, finally, the air does seem fresher, cleaner. Maybe it’s my imagination…
These Edmonton data come from the Edmonton Central Ambient Air Quality (AAQ) Monitoring Station located at 104 Street and 103 Avenue in downtown Edmonton (it’s on top of the building on the southeast corner). Summary graphs for these data can be found in Figure 1 and Figure 2.
Figure 1 shows that, for central Edmonton, NO2 readings have been going down over time since 2000, but that there are large (mostly predictable) daily and weekly swings in the data all within an annual cycle. As noted above, the NO2 these data represent comes from the burning of fossil fuels, and much of the NO2 from Edmonton Central comes from vehicle emissions. Since 2000, the ambient concentrations of NO2 have declined, mainly as a result of more stringent vehicle fuel efficiency standards.
Figure 2 (top image) highlights weekly trends where Saturday and Sunday have lower readings compared to weekdays; (bottom left image) weekdays have a ‘rush hour spike’ of emissions in the morning, and then a second, gentler upward trend for a more prolonged evening rush hour; (bottom middle image) readings are higher in the winter, likely due to more people driving, and climate conditions such as temperature inversions which hamper the dispersion of pollution.
In reference to Figure 3: Average March Readings from 2000 to 2020 (an explanation on how to read a box chart can be found at footnote 1 below). These data compare the average concentration of NO2 for the month of March from March 2000 to March 2020. The ambient concentrations of NO2 in March 2020 were almost 30% lower than the average of NO2 for March from 2015 to 2019 (footnote 2). That is a significant decrease.
What accounts for the improvement in air quality at this station? What portion is due to COVID-19? Is this 30% in NO2 an anomaly?
I’m not sure, but I am anxious to look at April’s data.
Acknowledgements
I’d like to acknowledge the Alberta Capital Airshed for sharing their data and creating all of the charts in this blog. Any mistakes are mine and mine alone.
Footnotes:
- Box charts can be tricky to read. A box chart is a cool way to show a summary of the data while also showing the calculated value. For instance, March 2020 shows a rectangle with a line through it. The line indicates the calculated average, while the rectangle shows where the middle 50% of the readings fall (half above the line, half below). The line below the box (a lower whisker) shows the smallest 25% of readings, and the line above the box (an upper whisker) shows the highest 25% of readings. The dots are outliers, meaning that they differ significantly (for a variety of reasons) from the other cluster of readings.
- In reference to Figure 3 which shows average NO2 Average Monthly March Readings from 2000 to 2020, March 2014 (18.8 ppb) and 2016 (17.3 ppb) both saw a lower average NO2 than 2015 or 2017-19, but higher than 2020 (15.2 ppb).
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