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Air quality improvement during COVID lockdowns less drastic than thought: Study

ABC News logo ABC News 1/13/2021
a view of a city: An empty street is seen in Wuhan, China, March 4, 2020. © Noel Celis/AFP via Getty Images An empty street is seen in Wuhan, China, March 4, 2020.

A potential silver lining of the devastating COVID-19 pandemic, a drop in greenhouse gas emissions because of the massive reduction in ground and air travel during lockdowns, may not be as drastic as previously thought, new research shows.

MORE: COVID-19 brought emissions way down in 2020, but what will happen when the pandemic is over?

Researchers in the U.K. from the University of Birmingham looked at 11 large cities -- Beijing, Wuhan, Milan, Rome, Madrid, London, Paris, Berlin, New York, Los Angeles and Delhi -- and discovered that although air quality did improve, it was by less than expected. Their findings were published Wednesday in Science.

Times Square street: New York's Times Square is seen nearly empty due to the COVID-19 pandemic, March 16, 2020 in New York. © Tayfun Coskun/Anadolu Agency via Getty Images New York's Times Square is seen nearly empty due to the COVID-19 pandemic, March 16, 2020 in New York.

When scientists separated the effects of the lockdown restrictions from weather and business-as-usual events, they found that clearing the air of secondary pollutants such as ozone and fine particulate matter may prove more complicated than reducing precursor emissions, such as nitrogen oxides and volatile organic compounds that result from chemical processes in the atmosphere.

MORE: How 2020 has changed the way many work and what may be here to stay

But while recent studies have explored the air quality impacts of the early 2020 lockdowns, many have not accounted for weather, which can moderate pollutant concentrations, according to the study.

a train traveling down train tracks near a building: An Italian Carabinieri car checks the traffic of the street around ancient Colosseum, in Rome, March 14, 2020, during the COVID-19 outbreak. © Andreas Solaro/AFP via Getty Images An Italian Carabinieri car checks the traffic of the street around ancient Colosseum, in Rome, March 14, 2020, during the COVID-19 outbreak.

Jason Smerdon, a climate scientist for Columbia University's Lamont Doherty Earth Observatory, told ABC News last month that transportation saw the largest reductions in emissions in 2020, accounting for about 40% of all reductions.

MORE: How coronavirus impacts climate change with emissions reductions

The study's authors found that reductions in automobile traffic led to an immediate decline in nitrogen oxide levels across all cities. However, less than 30% of the shift could be attributed to lockdown effects in most cases, in part due to continued emissions from other sources.

a view of a city: An empty street is seen in Wuhan, China, March 4, 2020. © Noel Celis/AFP via Getty Images An empty street is seen in Wuhan, China, March 4, 2020.

Ozone concentrations actually increased during the lockdown, the researchers found. Additionally, sudden decreases in particulate matter, isolated from weather and business trends, were not observed immediately after lockdowns began.

The research shows that massive drops in transportation-linked emissions are not a single solution to improving air quality but perhaps part of a larger, systemic overhaul, especially in cities, that takes into account "both primary emissions and secondary processes to maximize the overall benefits to air quality and human health."

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