In the wintertime, we see frequent cold fronts here in Kentuckiana that sweep away the unclean air and thanks to strong jet stream winds, we also get a lot of mixing between the lower and upper levels of the atmosphere to readily disperse pollution. However, these are luxuries that we don’t get to enjoy very often here during the summertime.

A major reason for the build up of pollution in the lower part of the atmosphere during the summer months is stagnant high pressure. High pressure is characterized by fair skies and light winds. Both of these characteristics promote the build up of pollutants near the surface where we live and breath. Fair skies promote the formation of ground level ozone under strong daytime heating and light winds don’t allow for polluted air near the surface to mix with cleaner air at higher altitudes.

These high-pressure systems tend to hang around during the summer months because of the location of the jet stream. The jet stream, the river of high velocity air aloft that steers weather systems across the globe, is normally located well to the north of Kentuckiana during the summer months. Without a push from those upper level winds, high-pressure systems often stagnate for long periods during the summertime. It is during these hot and dry stretches that we need to be extra cautious about the amount of pollution that we are helping to create.

So how does air pollution get removed during the summertime? The answer is water. Ever notice the residue that is left on your car windshield after a rain? That residue is pollution that has been removed from the air by the rainfall. Water is a very efficient recycler. Water constantly renews its purity by cycling itself from liquid into vapor and back again. It’s the constant recycling of water that also helps to restore purity to the air that we breath. You see with every raindrop that falls from the sky, pollutants are collected and carried back to the Earth.

Unfortunately, a few sprinkles of rain or a passing shower will not produce enough water to sufficiently clean the volume of polluted air that we have to deal with during the summer months. A thunderstorm, however, is a different story. Thanks to the intensity of rainfall during a typical summertime thunderstorm, the air under the storm undergoes a vigorous cleaning process. As an added bonus, evaporational cooling produced by the rainfall, also helps to reduce the temperature of the air making it both clean and comfortable. Think of it kind of like a gigantic outdoor air conditioning unit.

So the next time a thunderstorm passes over your house, go out side, take a deep breath and enjoy the clean air!