I'm sure most everyone noticed the nice haze-free conditions today. It definitely didn't feel like fall today, but the sky resembled it. The reason for this (the tropical air mass over the state) has been mentioned several times already in the forecast and in the blog. I figured, though, that it might be interesting to take a little closer look into summertime haze, and how a tropical air mass can help alleviate it.
First of all, most of my understanding of this process came from reading a paper by Stephen Corfidi of the SPC. In it he gives a detailed overview of summertime haze in the eastern U.S.
Haze is a common phenomenon in the Southeast during the summer. The whole process of how haze forms is fairly complicated, but basically haze is tiny droplets of condensed air pollutants These pollutants are both natural and man-made (anthropogenic), and they are mostly sulfates. There is some debate over whether anthropogenic pollutants are the primary reason for haze, but that is beside the point of this post.
Most people associate haze with warm, humid air moving in from the Gulf of Mexico, but in reality, research has shown that the air in which summertime haze usually forms is modified continental polar air. This continental air brings in both anthropogenic pollutants from Midwest factories and natural pollutants. Many times the air mass has an inversion at 850mb or so, and this traps the pollutants and the low level moisture in a very shallow boundary layer. This is the perfect recipe for haze.
A true maritime tropical air mass, though, is another story. Every now and then during the summer, a "surge" of true tropical air will rush into the Southeast. That is what is currently happening with the low pressure system over eastern Texas. As the system moves inland, it is bringing tropical air with it. Tropical air is more humid than continental air, of course, and that is one ingredient needed for haze. Yet, tropical air is much cleaner than continental air. An air mass that has been over water for days does not accumulate the type of particulates that a mass over land does. Also, a tropical air mass usually lacks an inversion, so the boundary layer is fairly deep, and any pollutants in the air are mixed into a much larger volume of air. So, all of this combined makes for haze-free conditions and a beautiful blue sky (between the clouds).
Drew McCombs
ABC 33/40 Weather Intern
abc3340wx2@gmail.com
First of all, most of my understanding of this process came from reading a paper by Stephen Corfidi of the SPC. In it he gives a detailed overview of summertime haze in the eastern U.S.
Haze is a common phenomenon in the Southeast during the summer. The whole process of how haze forms is fairly complicated, but basically haze is tiny droplets of condensed air pollutants These pollutants are both natural and man-made (anthropogenic), and they are mostly sulfates. There is some debate over whether anthropogenic pollutants are the primary reason for haze, but that is beside the point of this post.
Most people associate haze with warm, humid air moving in from the Gulf of Mexico, but in reality, research has shown that the air in which summertime haze usually forms is modified continental polar air. This continental air brings in both anthropogenic pollutants from Midwest factories and natural pollutants. Many times the air mass has an inversion at 850mb or so, and this traps the pollutants and the low level moisture in a very shallow boundary layer. This is the perfect recipe for haze.
A true maritime tropical air mass, though, is another story. Every now and then during the summer, a "surge" of true tropical air will rush into the Southeast. That is what is currently happening with the low pressure system over eastern Texas. As the system moves inland, it is bringing tropical air with it. Tropical air is more humid than continental air, of course, and that is one ingredient needed for haze. Yet, tropical air is much cleaner than continental air. An air mass that has been over water for days does not accumulate the type of particulates that a mass over land does. Also, a tropical air mass usually lacks an inversion, so the boundary layer is fairly deep, and any pollutants in the air are mixed into a much larger volume of air. So, all of this combined makes for haze-free conditions and a beautiful blue sky (between the clouds).
Drew McCombs
ABC 33/40 Weather Intern
abc3340wx2@gmail.com
on July 26, 2006, 7:38 pm
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on July 27, 2006, 5:57 am
Haze, ground level ozone, and particulate matter are related, but they're not exactly the same thing. Ground level ozone is formed when UV radiation from the sun splits up oxygen atoms. Oxygen atoms are "diatomic," meaning they naturally occur in pairs; when UV radiation splits that diatomic oxygen, the two individual atoms immediately connect to other oxygen atoms in the atmosphere. Since most of the other atoms are already bonded together, you get 3 oxygen atoms together instead of two, and that's what ozone is - triatomic oxygen. Ozone is harmful to plants, it damages rubber tires, and it causes respiratory problems.
Particle pollution is also called PM2.5, and it bears more of a resemblance to haze in that PM2.5 comes from vehicle exhaust, smoke stacks, and other usually man-made air pollution processes. These particles are left suspended around the source areas when winds are light.
The reason for Air Quality Alert days is to let us know when the concentration of PM2.5 and ozone at ground-level is unhealthy. There is always going to be some low-level pollution, but it's normally higher on hazy days since haze and high concentrations of ozone & PM2.5 are a product of pollution and a stagnant air mass.
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