Why Was London's Air Used

Double-click the movie above to understand the context.

A reader asked me this question:

• "Ed,
  
  I don't usually dwell on these things, but something on the GreenLink website caught my eye. Maybe it's nothing. Then again, maybe it's worth investigating. Here's a quote from the GreenLink website:
  
  London, Ontario airport meteorological data is considered representative of the Southwestern area of Ontario and recommended by the Ontario Ministry of Environment to use for dispersion modeling in this area. The wind rose for data collected at this airport in the year 2000 demonstrates that the prevailing winds in the area are coming from the west.
  
  Why is the City of Windsor using weather data from the London airport when DRIC is using weather data from Windsor airport, and their own monitoring stations on Huron Church Road? At the last CCG meeting, unless I heard incorrectly, I'm sure they said they were using Windsor data. They even had colourful graphs and diagrams.
  
  So has DRIC wasted all kinds of money setting up weather stations here when they could have simply used London data? Or is there something about the London data that differs from Windsor data that somehow casts the GreenLink plan in a more favourable light than if they were to use actual Windsor data?
  
  Maybe this is nothing. But to borrow a cliché, the devil is in the details. Perhaps this one is worth checking out."

I happened to be speaking to a fellow I know and he offered the following explanation. No, no, no...it has nothing to do with the suggestion that was made to use London's airport infrastructure as a model for Windsor's airport.

Is he right? I don't know. Perhaps Sam can explain it.

• "Ed, in the report for Greenlink they discuss the prevailing winds used for their study. They used London Ontario winds. These are the average winds used to determine which direction the runway should point. Using that we know the earth rotates east to west so the prevailing winds will most likely come from the west with moderate changes due to air pressures. Elementary meteorology.
  
  When they say London is a representative of Southwestern Ontario I tend to disagree. Wind data is READILY available at the Windsor Airport. The winds tend to be a little slower and higher due to the rising air from Detroit and southern Michigan.
  
  Ground level winds are always slower than the upper atmosphere, for examples.
  Windsor today is 220 at 6 knots
  London today is 220 at 9 knots
  At 3000' the winds are 230 at 12 knots.
  
  You can see the winds slow down closer to the ground as stated above.
  
  The asphalt and cement heats up and the hot air rises. This causes the winds to change direction and or slow down when the air mixes. Detroit does cause a lot of our weather.
  
  If you monitored the wind data difference Windsor would be always a little slower, not a lot, but none the less noticable.Considering the volume that is quite a bit of air.
  
  As a matter of fact the weather will always change dramatically once you pass Tilbury because the wind coming over Lake St. Clair is unobstructed.
  
  This being the case, London's overall air quality will be better because there will always be a higher volume of air moving.
  
  Since they used London's model they can assume there would be less parts per billion than there will be. Sort of like sweeter icing on a rhubarb cake.
  
  In their own statement...
  "Dispersion in the atmosphere depends on a number of atmospheric conditions that could either enhance or inhibit it. HIGH WINDS and UNSTABLE turbulent conditions ENHANCE DISPERSION while stable atmospheric conditions and low wind speeds don't promote mixing. In addition, pollutants tend to disperse downwind."
  
  By tunneling you are CONCENTRATING the toxic fumes by not letting them disperse freely in a higher volume of air.
  
  In doing so, even the jet fans will not be able to disperse the fumes and since they are heavier due to concentrate they will fall to the ground closer to the tunnel exhaust portals than farther. Particulate matter is not lighter than air.
  
  Has pollution ever dispersed upwind? Right. That is quite a revelation for an engineering report.
  
  Hope I explained it."