Meteorologist Dennis Fudge is still sniffing the wind to find the source of the sulphur belch that wafted over Prince George last month.
It was detected by noses all too familiar with the reek that used to be blamed solely on the pulp mills. It was also detected by the Ministry of Environment's Total Reduced Sulphur index, which collects a handful of different sulphur-based chemicals in the airshed and marks the total amounts. A typical day has between 7 and 20 parts per billion in the local atmosphere, but those July readings spiked into the hundreds (350 parts per billion was the worst single value).
"We know a specific direction, but not a specific spot, yet," said Fudge. "We are doing things now like calculating wind speed and wind direction to apply to the other known data."
It is almost a certainty that the smelly emission - it was not significantly harmful to health - came from an industrial source like a mill or factory. Several candidates exist. At the time, all reported nothing amiss in their operations.
"Whatever occurred started around the 24th of July," Fudge said. "The thing is, it is hard to nail down because if you had south winds for a few days prior, then got the wind shift, that could mask the date it began. But detection started to show the signs at July 24."
Fudge said there were high amounts of that category of sulphur again on Monday - about 30 parts per billion - along with higher values in other categories as well like particulates and sulphur dioxide.
"That indicates it came from a stack [not a ground source] - a typical fumigation event on a stagnant, clear night," said Fudge. It typically happens when industrial plumes get trapped, then brought back down to the ground in the normal daily cycle of warm/cold air inversions.
"Lately - the last two years or so - we don't get the high values we used to get on a regular basis years ago," he explained. "We still get events but nothing like it was. I would credit the upgrades at the pulp mills - their boiler improvements. But then again, it could go back to meteorology as well because we aren't getting the morning inversions, either, that we used to: less frequent stagnant nights, less frequent light breeze nights. We have had more windier conditions. The true data is not all added up for that, though, we have to look at all sides of that before we make a conclusion. Now we are starting to get a bit more stagnant conditions so that could be behind the fumigation events really recently."
The conditions that held our nose to the stinky substance is one element of research, but the priority question Fudge is centred on is what caused this large wave of stinky stuff to be up in the air in the first place.