This laser-firing truck could help make hot cities more livable

when you go On a road trip, you pack snacks and drinks and make sure you have good music to line up with. Climate scientist Katia Lamer, on the other hand, packs party balloons loaded with atmospheric sensors and then climbs into a laser-firing observatory on wheels.

Lamer — operations manager at Brookhaven National Laboratory’s Center for Multiscale Applied Sensing — recently completed a 1,700-mile trip from Upton, New York, to Houston, Texas, in a specially designed science truck while taking a bevy of measurements from air to temperature moisture to wind. The big plan: a better understanding of the complex climate dynamics of cities, where conditions can vary greatly not just from neighborhood to neighborhood, but from door to door.

“The big difference with urban environments is that they are much more heterogeneous than natural environments. That means there are more elements, like individual buildings, that make up these canyons,” says Lamer, referring to the corridors between the buildings. “So when the surface is more complicated, that leads to some changes in meteorology at a much finer scale than we would have if you were looking at a unified ocean.”

Climate scientists have a good grasp of how natural green spaces like grasslands and forests affect their local conditions: When plants photosynthesize, they exhale both oxygen and water vapor, which cools the air — vegetation essentially sweats. In contrast, a city’s built environment — concrete, glass, brick — absorbs the sun’s energy very efficiently, heating urban areas by up to 20 degrees Fahrenheit above surrounding rural areas.

This is known as the urban heat island effect, a complicated phenomenon that Lamer is attempting to measure with her observatory on wheels. The truck is equipped with a lidar sensor that fires lasers to track airborne particles to measure airflow. (Self-driving cars also use lidar to map their surroundings in 3D, but these lasers bounce off obstacles like other cars.)

This flow can vary significantly depending on the size and orientation of the buildings in a given area. For example, two adjacent structures of the same height form a vortex that runs up one side and down the other. “What if you stack two buildings back-to-back, like if they’re different heights, how does it all affect the local weather? So that’s a kind of limit,” says Lamer. “In each neighborhood, each side of each building has its own microclimate.”

When the sun heats one side of a building, it makes this air movement more difficult as hot air rises. But on the shady side of the building, there may not be the same upward movement. Add wind to the mix and you have atmospheric dynamics that change on very subtle scales, both spatially and over time. “It’s a very turbulent process when the wind moves through this urban canopy,” says Vivek Shandas, who studies the urban heat island effect at Portland State University but was not involved in this new research. “The science behind it really didn’t understand how the roughness moves the wind and how it actually affects an entire cityscape.”

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