Pandemic lockdowns have reduced air pollution, but with a catch

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Last April, like people around the world protected against the Covid-19 pandemic, The Indian Express newspaper posted a photo which had gone viral on Twitter, showing a slightly hazy deep blue sky over Uttar Pradesh, the most populous state in northern India. Above a garden trellis, the angular, white peaks of the Himalayan mountains were visible on the horizon like a stiff whipped meringue. Pawan Gupta, a senior scientist with the University Space Research Association at NASA’s Marshall Space Flight Center, said friends and family in India told him the peaks had not been so noticeable since. decades. The reason is simple: Before the pandemic lockdowns, the air was filled with smog.

Gupta studies air pollution in India and, like many other scientists, is studying how lockdowns have reduced emissions over urban areas. “It’s a natural experience for a lot of us,” Gupta says. A natural experiment that has proven one thing above all: air quality can improve, and quite quickly too.

In one published study in March Sustainable cities and society, Gupta and his colleagues focused on three months – from March to May 2020 – in which travel, construction and industry outside of medical facilities was limited. They compared the air pollution measurements of six metropolises – Bengaluru, Chennai, Delhi, Kolkata, Mumbai and Pune – to the same period over the previous three years. Using satellite imagery, they found a 42 to 60 percent reduction in particulate matter and a 46 to 61 percent decrease in nitrogen dioxide (NO2), a potentially toxic air pollutant.

Special case, the scientific term for soot, includes soil, dust, smoke, and allergens. Very tiny particles can find their way into people’s lungs and bloodstream, making bronchitis worse, causing heart attacks and even speeding up death. NO2 is produced by burning fossil fuels and can make asthma worse and increase the risk of respiratory infections.

Gupta’s colleague Christoph Keller, a senior scientist at the same NASA research association, is also monitoring urban air pollution. For Keller’s study, Posted in Atmospheric chemistry and physics in March, he created a basic computer model for what the global NO2 emissions would have been in 2020 without any lockdowns. Then it used area measurements to track actual emissions in cities around the world, including Melbourne, Taipei and Rio de Janeiro. Its results showed a global NO2 down nearly 20 percent, and 50 of the 61 cities analyzed showed reductions of between 20 and 50 percent. Notably, Wuhan, China showed a 60 percent reduction; for New York it was 45%.

“One of the lessons we can learn from the pandemic is that there is still great potential to reduce NO2 concentrations, ”says Keller. “What we clearly see in urban environments is that there are still a lot of NOs2 it’s an artificial product that we can really reduce a little bit. “

Other recent studies have echoed the same findings. Marco Carnevale Miino, doctoral student in engineering at the University of Pavia in Italy, 22examined NO2 concentrations in three European cities. It found it was down 80.8% in London, 79.8% in Paris and 42.4% in Milan between March and May this year, correlating with the drop in traffic caused by travel restrictions. In Santiago, Chile, researchers studied urban air pollution during those same three months and compared them to the same period over the previous three years. They also found that the average particulate matter and NO2 concentrations were decreasing. 22In Portugal, researchers found that NO2 dropped by 41% and particles by 18% during the period from March to May compared to the last five years. Researchers from the UK have studied NO2 data from January to June 2020, and again found that concentrations decreased by 32-50% during the lockdown and gradually increased as road traffic returned.

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