LA has just experienced one of the hottest summers in history during the past two months, thanks to something called the “urban heat effect.” Imagine wearing a black t-shirt on a hot day instead of a lighter-colored one. Similarly, an urban heat island (UHI) is created when the city is covered with dark surfaces such as asphalt and concrete, which absorbs more solar radiation and thus gains more heat than the surrounding suburbs. City buildings that block the wind also contribute to this effect.
“Normal land has, what we call an ‘albedo,’” said professor Dr. Victoria Petryshyn, an expert on geobiology and environmental science at USC. “Albedo is essentially how much reflects versus how much gets absorbed. Something that is completely black has an albedo of 0. Something that is perfectly white has an albedo of 1. And most materials fall somewhere in between. So, when you paint the land black, you put a lot of asphalt, you put a lot of buildings, you lower the albedo and you end up absorbing more heat, and this heats up cities.”
But now, Los Angeles is taking an ambitious and creative action to reduce the urban heat effect. By covering the land with cooler pavement across 15 council districts, Los Angeles began dressing its streets in white this year in a pilot program, hoping that a lighter color will reflect more sunlight and absorb less heat.
According to Marcos Silva, a resident of Lord Street near the USC Health Science Campus, which recently got white streets, "[Officials] checked the temperature in different places, across the whole street. And that's the only street [in this district] that is this white color and other ones are black."
So far, this program has received positive feedback with a notable temperature decrease on these “white streets”.
“You can feel the difference, and at night too. And in summer, when it was hot, you’d feel way fresher. It does make a difference,” said Gustavo Gonzalez, another resident of Lord Street.
According to Dr. Victoria Petryshyn, the test program is promising also in terms of less energy use: “Rather than having asphalt be black and absorbing all that heat, they are just raising the albedo a little bit so it would reflect a little bit more. And the hope is that if you reflect a little bit more, you reduce the overall temperature. You reduce the needs for things like air-conditioning, which is going to reduce your dependence on energy fossil fuels. And then also people who can’t afford air-conditioning, or people who are out working in the heat get a break from it as well,” she explained.
However, one thing that came to residents’ notice is that the color of the “white street” has gradually changed into grey over time. “The color was really white but it turned grey,” said Gonzalez.
“You can see a difference of the color of the street… the color was kind of white but right now the color is kind of grey,” said Silva.
This raises some questions about the sustainability of these white or grey streets, including how long it will take before the streets have to be repainted, whether residents still get the effect of the cooler pavement after it fades into a greyish color, and the associated energy costs of repainting the streets.
Dr. Victoria Petryshyn pointed out another potential issue with lighter streets. "One of the bigger concerns I have heard about is whether there will be sunlight reflected in people's eyes [while driving]," she said.
“But I think LA is being really smart about this because they are doing a test pilot program,” she added. “So rather than just painting all of our streets, they will collect some sample data on it and actually see ahead of time what we can expect and whether we can actually scale this up to a citywide production.”