One of the few uplifting developments in the early weeks of the COVID-19 pandemic was the remarkable boost in air quality around the world.
Did the clean air mean anything? Was it evidence that collective action could clean the air faster than many thought possible, or just a fluke of the weather, or proof that even radical steps couldn’t fight climate change? The answer, UCLA air quality researchers say, isn’t precisely any of these but includes elements of all three.
A December 2020 study led by Yifang Zhu (professor of environmental health sciences at UCLA Fielding School of Public Health) found that while favorable spring weather helped, traffic reductions in Los Angeles last March and April were directly responsible for a roughly 30% decrease in nitrogen oxides, a common tailpipe emission. Once the lull in traffic ended, however, the pollutants returned.
After pollutants from traffic briefly declined, ozone increased, including a massive spike in April, said Suzanne Paulson (UCLA professor of atmospheric and oceanic sciences and a member of the UCLA Institute of the Environment and Sustainability), citing figures from the South Coast Air Quality Management District. Ozone, which serves as a barrier against the sun’s ultraviolet radiation in the stratosphere but also contributes to smog at ground level, can be increased by tailpipe emissions, but it’s not a one-to-one equation — traffic isn’t the only contributor.