SAVANNAH, Ga. (WSAV) — We all know how hot the ground feels under our bare feet after we exit a pool and how much better it feels in the grass. But why does it feel better in grass that has also been in the sun the entire day? It is sort of like how t-shirts heat up in the sun. In this episode of Exploring the Atmosphere with Alysa, I’ll explain why surface materials heating up in the sun breaks down to two things.
3 Main Ground Materials
These are the 3 main ground materials we see around the area: asphalt, concrete, and grass. I tested their temperatures using my infrared thermometer at 2 pm on July 31st, which was one of the hottest days this summer so far.
I was able to find a section of asphalt, concrete, & grass all next to each other. So let’s test it. Out in the summer sun, asphalt is the hottest at 142 degrees. Concrete comes in second at 119 degrees. You can see how quickly the temperatures of these materials cool down in the shade.
Asphalt is a darker color. The darker the color, the more energy is absorbed from the sun. This is no surprise that it is the hottest material out of the three. But how will grass compare?
With grass you wouldn’t think it would heat up that much. However even in the sun, it warmed to 100 degrees. While grass also absorbs the sun’s energy, it is absorbed through a different process called photosynthesis. The sunlight is food for grass. As grass absorbs heat from the sun and CO2 in the air, it converts both into a chemical energy it needs to live. Instead of emitting heat into the air, the grass then releases oxygen.
Why do Certain Materials Heat up More Than Others?
It comes down to two things: the material of the surface and how much solar radiation it receives and then emits. Concrete and asphalt have a higher capacity for heat. This allows them to heat to higher temperatures and then release that heat more slowly compared to other materials.
In the full blown sunshine, the ground receives an abundance of solar radiation. As the ground heats up, it emits some of the heat back into the air and atmosphere. With asphalt having a higher capacity for heat, it is able to emit more than concrete and at a slower speed. This increases the air temperature right above the asphalt for a longer time. This is why it feels extremely hot when you are standing in the middle of an asphalt parking lot.