Pollution Thunderstorm Chasers on the Hunt

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Atmospheric scientists are out chasing the biggest thunderstorms the U.S. can dish out. But they’re not drawn to tornadoes or floods — they’re tracking down pollution.

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Big thunderstorms notoriously suck up ground-level air and pollutants like a vacuum and vent them high into the sky. Now it’s time to figure out how much pollution goes up and what happens when it gets there, say the scientists behind a new field campaign known as Deep Convective Clouds and Chemistry, or DC3.

To be clear, it is fine to think of a “deep convective cloud” as a big thunderstorm: “When you see or hear a thunderstorm, it is really a mature convective cumulus cloud,” the DC3 team clarify on their blog. “So what you might call a boisterous thunderstorm is in fact a deep convective cloud!”

The campaign, which began May 15 and runs through June 30, is targeting thunderstorms across Colorado, Oklahoma and Alabama. A team of 100 scientists from 29 organizations, including the National Center for Atmospheric Research, is using three research aircraft, among many other tools, to quantify the influence of thunderstorms on air chemistry at the top of the troposphere (the lowest layer of the atmosphere, where all of our daily weather occurs).

In the photograph above, taken over central Oklahoma four days into the DC3 campaign, the wispy, gray clouds near the tip of the airplane wing form a distinctive anvil shape that marks where rising clouds slam into the boundary between the troposphere (where air moves mostly vertically) and the stratosphere above (where air moves mostly horizontally).

 WIDE ANGLE: TORNADOES

 WIDE ANGLE: TORNADOES

The DC3 team is particularly keen to quantify ozone concentrations in this relatively uncharted territory of the sky. At other altitudes, ozone can be a good thing*, but in the upper troposphere it acts as a powerful heat-trapping greenhouse gas.

They are also keen to quantify concentrations and sources of nitrogen oxides (NOx), which eventually produce harmful ozone through a series of chemical reactions in the presence of sunlight. Lightning strikes produce some NOx, but much more comes from human activities on the ground (fossil fuel combustion and agricultural and forest fires). DC3 analyses will be able to tell which is which.

* Ozone’s status depends entirely on its altitude. Here’s a quick summary:

  • Ground level = bad = Ozone is a damaging pollutant and human health hazard.
  • Middle troposphere = good = Harmful pollutants are destroyed and turned into ozone.
  • Upper troposphere = bad = Ozone is a potent heat-trapping greenhouse gas.
  • Stratosphere = good = Ozone absorbs a large percentage of harmful ultraviolet light from the sun.

 

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Photo: Distinctive anvil-shaped top of a thunderstorm cloud over central Oklahoma on May 19, 2012, viewed as the Gulfstream-V aircraft approached from the south. Credit: Chris Cantrell, National Center for Atmospheric Research.