Anyone know what this is all about? Air quality alert for Chicago, MN-St. Paul and Rochester?

[Mind_your_head]

http://www.weather.com/outlook/health/airquality/?state=IL#IL
(says 'fine particles' and then 'action day')

What sort of particles? From what source? What kind of 'action'?

I'm perplexed. :shrug:

Can anyone shed some light here?

....and then there is this:

http://www.weather.com/weather/alerts/localalerts/USIL0828?phenomena=TAQ&significance=TL&areaid=ILZ013&office=KLOT&etn=0000

THE ILLINOIS ENVIRONMENTAL PROTECTION AGENCY AND THE INDIANA DEPARTMENT OF ENVIRONMENTAL MANAGEMENT HAVE DECLARED THURSDAY FEBRUARY 4 AN AIR POLLUTION ACTION DAY DUE TO ELEVATED POLLUTION LEVELS.

[jillan]

1. I live in Phoenix and we get those kind of days alot.

For us it's when the air has been still for several days in a row, no wind or rain.
The particles are in the air and they are not being cleaned out by nature. Has your air been "stagnant" for a few days?

[PeaceNikki]

2. Here

http://www.wbbm780.com/Air-Quality-Alert-Issued-For-Chicago-Area/6286980

[Mind_your_head]

3. Interesting - thanks

Although I can't help but kind of *snicker* about 'factories' contributing to the pollution....we have sooooo fewer factories than we used to "back in the day".

edit to add: still doesn't explain the "action day" thing though.... :shrug:

[lunasun]

4. I'm In Chicago

(and I know warmer weather places year round may get these) but I agree , up here in the upper midwest
you never hear about these action days in the dead of winter! Only when it gets warmer out
Made me pause from making the coffee today when I heard it on the morning news. How can that be? it is 24 degrees out! Hope someone can explain

[Warpy]

5. Temperature inversion, most likely

That's when a warm air mass aloft sits on top of a colder mass of air at the surface. Pollution is trapped within the cold air as the warm air acts as a blanket to hold it all in, shutting down the convection currents that usually keep the air mixed.

You've never seen filthy air like it was back in the 50s, though, when people still used coal for heating their houses. Inversions then could kill.

Just because their explanation is better than mine: http://en.wikipedia.org/wiki/Inversion_%28meteorology%29