Yesterday I was driving into downtown Chicago for day two of Lollapalooza. One of my favorite views of my regular life is seeing the Chicago skyline in the distance as I drive down the Edens Expressway. Yesterday, however, it looked like the city was engulfed in fog...serious fog...London-esque fog. The problem was, it wasn't fog. In fact it was 87 degrees out, which is hardly foggy weather. It was one of the haziest days I had ever seen living in Chicago and it got me to wondering, what exactly makes the air so hazy on a given day.
I'm aware of ozone action days, and know that they are caused by high levels of ground ozone due to auto emissions, factory pollutants, and aerosol cans. Ozone action days occur between May and October and are highest in the Midwest. There have been several ozone action days recently, probably because it's between May and October here in the Midwest (crazy how that works), but the city has not been shrouded in haze. What made yesterday different? I checked several weather website, and of course Wikipedia to see what I could find.
It turns out that air quality can worsen when the pollutants build up because they are not diluted by fresh air. When the air is stagnant, say from a lack of wind, the air pollution remains in the same area and this localization of the pollutants leads to haze.
Judging by yesterday's haze, the pollutants were as crammed together as we were at the Red Hot Chili Peppers Lolla set. However, since the rain had cleared the air in Chicago, the haze we were surrounded by at the concert last night was from a decidedly different type of pollutant.
you drove to lollapalooza??
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