On Monday, November 15, India’s Supreme Court proposed a lockdown in New Delhi. Their proposal called for the suspension of all nonessential travel and for tens of millions to work from home. Two days later schools were closed, construction work was halted, and coal-fired power plants were shut down.
Wait, what? Those last two may have thrown you for a loop—both are pretty odd twists to COVID lockdowns, aren’t they? Well, the lockdowns last month in New Delhi weren’t because of COVID, but rather because of fine particulate matter levels measured at 10 times the World Health Organization’s daily PM2.5 limit of 15 µg/m3.
I must admit when I first saw headlines about lockdowns in New Delhi my mind immediately went to COVID—I guess that’s the world we live in now. But then I got to thinking about how the pandemic has given us a unique opportunity to compare air quality before and after various reactions to COVID.
The World Meteorological Organization (WMO) has found that the vast majority of the world experienced a reduction in air pollution levels in 2020, thanks in large part to changes in traffic and energy production. An interesting chart from the WMO of pollution reduction by continent and some countries can be found here: https://twitter.com/WMO/status/1433790577615806467/photo/1
If you look carefully at the WMO chart, you’ll notice that pollutants decreased just about everywhere during lockdowns—with the exception of ozone which was either basically the same or even a bit higher during the lockdown. That’s because nitrogen oxides destroy ozone in the atmosphere, so in some locations when nitrogen oxide levels dropped, ozone was able to thrive.
It’s also interesting to note that there were natural events that in some locations overwhelmed COVID-related pollution reductions. For instance, the largest African dust storm ever observed—dubbed the “Godzilla Storm”—occurred in late June 2020, sending 24 million tons of dust across the Atlantic Ocean toward the Caribbean
(https://www.science.org/content/article/godzilla-dust-storm-traced-shaky-northern-jet-stream); I can remember some gorgeous sunsets where I live in Maryland thanks to the “Godzilla Storm.”
There also are some locations where local customs/practices ensured that air pollution levels remained very high despite COVID lockdowns. While you likely think of cities in India and China as consistently having some of the worst air quality in the world (and you’d be right), it may come as a surprise that some of the world's highest levels of air pollution are measured in Belgrade, the capital of Serbia. Belgrade’s air pollution is primarily driven by coal-fired industry nearby but there’s also another component that is somewhat unique to Belgrade—many of its 1.4 million residents burn lignite in their homes for heat in the winter, which leads to very high pollution levels throughout the city in the colder months. So even as traffic has been greatly reduced in Belgrade thanks to people working from home, businesses and schools being closed, etc., residents have continued to burn very dirty fossil fuel in their homes for heat. As a result, pollution levels in Belgrade have remained very high, despite all the measures taken during the pandemic.
All of this supports a central theme I try to get across to students when I speak about air pollution at local schools (at least when I did before the pandemic!). That theme is that air pollution, like most things, is far more complicated than many people give it credit for. Reducing one pollutant’s emissions (nitrogen oxide) can actually lead to higher levels of another pollutant (ozone). New Delhi can shut down its local industry and prevent its citizens from driving their cars, but that won’t keep pollution from the nearby state of Punjab (for example) from blowing into New Delhi. Puerto Rico can force people to work from home and take cars off the streets, but they got hammered in the summer of 2020 with the highest levels of Sahara Dust ever seen. Belgrade can lock its people down and keep them in their homes, but that doesn’t stop them from burning lignite in their fireplaces when they’re there.
Certainly, the pandemic has been a dreadful thing for the world to endure. Not that it comes close to a silver lining, but it has afforded us an unprecedented opportunity to compare air quality between two very different emissions scenarios. And while air quality has improved overall, be careful to speak in absolutes—in some places the air quality has remained the same, and in some places it has actually gotten worse.