Here's why air quality in Regina spiked to 'very high risk' in the middle of winter

Traffic during winter conditions in Regina can be seen in this file photo. (David Prisciak/CTV News)

Those watching Environment Canada's Air Quality Health Index (AQHI) for Regina might’ve been a bit puzzled when the city reported a value of 10+ or “Very High Risk” early Sunday morning.

Elevated air quality readings were reported in Regina beginning on March 2 – when an AQHI reading of four or moderate risk was noted, according to the weather service’s records.

The readings continued to rise until they reached 10+ from 5 a.m. to 9 a.m. on Sunday. The readings even necessitated a special air quality statement.

While Regina saw its fair share of "high risk" air quality during last year’s wildfire season – the readings remain odd while the province is gripped in winter storm conditions.

According to Environment Canada and Climate Change (ECCC) meteorologist Justin Shaer – the standout readings had a very simple explanation.

“There was an increased level of NO2 that was reported at one sensor that was causing the spike in air quality. So that was related to the refinery I believe,” he said in a message to CTV News.

A combination of wind and pure luck caused a large portion of emissions from the Co-op Refinery Complex in northeast Regina to be blown directly at the ECCC sensor for several hours. The sustained readings were aided by storm conditions, according to Shaer.

“It was blowing right into the sensor which created the elevated readings and with the nice thermal inversion we’ve had in place earlier today – it really concentrated the values down,” he explained.

ECCC air quality records show AQHI values consistently fell through the afternoon as weather pattens shifted – eventually arriving at the seasonal average by 6 p.m.

“Now we’ve switched to a westerly wind and it all kind of flushed out and the air quality is back to what we usually see for Regina during the winter – which is around a two or a three,” Shaer added.

Nitrogen oxide (NO) and nitrogen dioxide (NO2) are both common air pollutants. According to the ECCC, NO is formed primarily from the liberation of nitrogen contained in fuel and nitrogen contained in combustion air during combustion processes.

NO released during combustion quickly oxidizes when it reaches the atmosphere and becomes NO2.