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Short-term changes in weather as pollution falls amid COVID-19

Thursday, June 4th 2020, 7:04 pm - Decreasing levels of particulate matter have caused wind speeds to slow down in some heavily polluted areas, as well as some localized changes in surface heating.

Policies that were implemented to slow the spread of COVID-19 greatly limited the frequency of road and air travel, which has caused skies to clear and pollution levels to fall.

The impacts on environmental and human health from less pollution are apparent and expected, as we know of the toxic and harmful consequences of greenhouse gases. What is less obvious is the impact that decreased pollution levels have on the weather.

Mark Jacobson, professor of civil and environmental engineering at Stanford University, says that lower amounts of soot, black and brown carbon and other dark particles that come from diesel exhaust, jet fuel and polluting energy sources are having short-term changes in regional weather around the world.

“Dark particles absorb sunlight and they heat the air relative to the ground, so they make the air more stable, so it’s more difficult for air to rise and sink,” Jacobson explains.

“You can actually slow down the winds near the surface by having dark particles in the air.”

Several regions around the world experienced changing winds as pollutant levels dropped, including China where wind speeds slowed down. Jacobson says that the changes in wind speed caused by dark particles are subtle, but it can be noticed in some heavily polluted areas.

wikipedia smog in china A day with heavy smog versus a sunny day within a 10-day interval in Fanhe, China. Credit: Tomskyhaha/Wikimedia Commons. CC BY-SA 4.0

Another parameter that is being impacted by varying pollution levels is temperature.

Mario Picazo, a professor in the department of meteorologist at University of California Los Angeles (UCLA), notes that preliminary research suggests that the sudden decrease in particulate matter is blocking less sunlight, which means that carbon dioxide and other greenhouse gases could absorb more of this energy and create a short-term warming effect.

“It’s a bit contradictory to a lot of people who say, ok, you are taking away pollution but you’re going to get warmer,” Picazo says.

White and gray particles are also pollutants that are released when fossil fuels are burned, which are more reflective than dark particles. Their lighter colouring reflects sunlight away from the Earth, which creates a cooling effect on the ground.

“There are more light particles than dark particles, so if you actually clean the air you are removing more of the reflective particles than you are of the heating particles and as a result, you are warming the ground [in the short term],” Jacobson explains.

Ideally, light and dark particles would be removed simultaneously with greenhouse gases to create a long term decrease in global temperatures. Jacobson says that doing this, as well as eliminating all polluting emissions from human sources, is possible by transitioning to renewable sources for all of our energy needs.

To learn more about how decreasing levels of pollution are impacting the planet, watch the full-length interview with these experts below.

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