11:45 25.08.2020

China’s Coronavirus Lockdowns In February Decreased Some Air Pollution But Not All

Source: Forbes
China’s Coronavirus Lockdowns In February Decreased Some Air Pollution But Not All

In late March, a popular meme on Twitter posited the Covid-19 shutdowns across the globe were a cure for pollution. “Nature is healing, we are the virus” went the slogan. While the phrase was used satirically — the first viral tweet to use it featured a photo of scooters floating in water and read “the lime scooters are finally returning to the river” — it was born from earnest, viral stories of wildlife appearing in quarantined cities. One such tweet with pictures of swans supposedly in the canals of Venice attributed lockdowns to clearer waters and the return of the birds and other tweets told of dolphins in the canals and tea-drunk elephants in the Yunnan province. 

However, most of the claims were misleading or flat out false (in the first case, the swans were not in Venice, but another Italian town, Burano). Still, is there a scientific basis for the idea that the pandemic has paved the way for nature to “heal”? A recent study published in Geophysical Research Letters provides new insight on the environmental effects of lockdowns. The researchers from the University of Washington analyzed the effect that China’s quick and strict limits on travel and gatherings in February had on regional air pollution.

“We asked the question: did the lockdown measures China put in place to stop the spread of Covid-19 lead to a decrease in air pollution?” says author Michael Diamond, a doctoral student at the university’s Department of Atmospheric Sciences. “And our answer was yes… and no. It depends on what kind of pollution you’re talking about!”

The team found there was an unprecedented drop in nitrogen oxides, a form of air pollution which disproportionately is produced from passenger transportation, such as from the tailpipes of cars. However, there were no significant changes in aerosol particles in the atmosphere or in cloud properties. 

Diamond studies the interactions between pollution and clouds. Aerosols, tiny particles suspended in the air, play a role in cloud formation and as a major component of air pollution. “Water in the air needs an aerosol ‘seed’ to form around to actually become a cloud droplet,” Diamond explains.

In air with more aerosol, more droplets will form than in cleaner air. Clouds with more droplets are brighter, reflecting sunlight back into space and creating a cooling effect which, according to Diamond, “masks” some of greenhouse gas induced global warming. So, understanding aerosols and cloud droplets is critical to understanding how much the earth has warmed and how much warming there will be in the future.

China’s lockdowns provided a valuable “natural experiment” — a dramatic disruption from the normal through which researchers could gain further knowledge on aerosols and air pollution.

To best understand how China’s lockdowns impacted air pollution, the researchers took into account a variety of outside factors, including environmental policies enacted over the past decade and meteorological anomalies. For example, February 2020 was warmer and wetter than average, which potentially contributed to lower nitrogen dioxide levels, as well as provided higher potential for aerosol production. They even accounted for the atmospheric effects of Chinese New Year, which occurred in late January right before lockdowns, such as lessened traffic emissions and an increase in particles from fireworks. 

These various factors are critical for a full understanding of the data. Air laws in eastern China have contributed to downward trending pollution levels since 2013.

“Even without any effect from the Covid-19 lockdowns, February 2020 would have been expected to have less pollution than the 2013 to 2019 average!” says Diamond. “In the case of aerosols, you would incorrectly conclude that there was a big decrease due to Covid-19, and thus may start looking for a cloud signal that shouldn’t exist in reality.”

After taking all these variables into consideration, the researchers found the lockdowns led to a 50 percent drop in nitrogen dioxide from what would be expected for February 2020. The drop is incredibly striking — it’s more than twice as great as anything seen on the record over the last decade and a half. 

The reason for the striking drop in nitrogen dioxide but not aerosols is that in lockdown, traffic can disappear virtually overnight and effectively curtail the emissions of nitrogen oxides. But, while transportation halted quickly, heavy industry remained more or less constant during the course of shutdowns in China. If power plants adjusted over a longer period of time, it could lead to lower aerosol levels in the future.

“The air pollution changes we saw during the February 2020 shutdown in China does perhaps offer a glimpse of a possible future in which transportation emissions decrease dramatically, perhaps because of widespread electrification of cars and trucks,” Diamond says. However, “if we want to improve all aspects of air pollution, we’re going to need a comprehensive portfolio of policies to tackle emissions in many different economic sectors at the same time.”

Tackling air pollution is also a matter of public health, especially during a pandemic of a disease which targets the lungs. Researchers are still looking into connections between air quality and vulnerability to Covid-19. Some evidence from the 2003 SARS epidemic suggested short-term exposure to air pollution led to higher fatality rates in China. If change in pollution has an impact on Covid-19 fatality, Diamond suggests taking reduction measures into account may help reopening strategies.

As for the idea on Twitter that nature is healing itself and we are the virus, Diamond urges we center care for other humans in discussions of environmental change going forward, and cautions the drop in pollution from lockdowns is “incredibly short-lived.” 

“Lasting change is going to have to come from a more deliberate societal response — I don’t think anyone would seriously argue that life under quarantine is a good model for a more sustainable future.”

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