The secret behind Houston's clouds? Scientists say it starts at one power plant

Scientists may have found one of the biggest reasons Houston is so good at making clouds, and the findings could be both fascinating and unsettling. 

Researchers at UC San Diego identified the W.A. Parish Generating Station southwest of Houston as the dominant source of cloud-forming aerosol particles over much of the metropolitan area. In other words, scientists found the plant's emissions produce the tiny airborne particles that help clouds develop over Houston.

In fact, researchers mapped the plant's plume stretching over downtown Houston before extending more than 65 miles downwind, making it the dominant source of cloud-forming aerosols measured across much of the Houston area.

"We are aware of the study and reviewing its findings," a spokesperson for NRG, W.A. Parish Generating Station's parent company, told Chron in an emailed statement. "Houston's air environment includes many sources, and this excerpt/article reflects one piece of a broader picture. What we can speak to is how we operate: meeting all local, state and federal regulatory standards with controls and significant monitoring in place. We support regulations grounded in sound science that ensure/uphold the safe, reliable, and affordable production of electricity, and we work closely with regulators and local communities to uphold those standards."

As fascinating as the findings are, the researchers said they also carry an important public health message. Although the study focused on cloud formation, lead author Greg Roberts noted the same particles that help clouds form are also the size most commonly associated with respiratory illness.

"Cloud-forming particles are also the size of particles that go deepest into the lungs," he said in a public statement. "There's always been a layer of doubt as to where those particles are coming from."

The findings may also help explain one of Houston's stranger weather mysteries. Earlier this month, unusual cloud bands appeared to line up almost perfectly above several of Houston's major freeways, leaving even local meteorologists searching for an explanation. While Roberts said the coal plant study could not exactly tie them together, he told Chron in an emailed response he found the cloud formation over the highways "very interesting," and the phenomenon is scientifically possible.

"While rare, these clouds are scientifically possible as cloud formation hinges on a balance between heat, moisture, and condensation nuclei (tiny particles that serve as seeds for cloud droplets)," he explained. "For clouds to form over a freeway, there needs to be a perfect combination of light winds (that allow air to stay over the road rather than being swept away), high humidity (that supplies abundant water vapor), and strong surface heating of the wide freeways as the sun rises (which warms the pavement, causing the air to rise)." 

Roberts also noted that warm, moist vehicle exhaust can help air rise, giving surface heating "an added boost" and creating the right conditions for narrow bands of cumulus clouds to briefly develop over highways.

"While the interstate-induced clouds were short-lived, this is a clear and cool example of how urban centers can impact local weather conditions," he concluded.

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