The coronavirus pandemic has put much of the world into lockdown, with factories going idle and city streets turning into eerily empty walkways. With the case count and death toll still climbing, it’s unlikely that countries will be able to flick a switch and rapidly return to pre-pandemic economic activity.
But one unintended upside to this crisis has been improved air quality, particularly in the hardest-hit areas where the most draconian measures have gone into force. This has been evident in Asia, including China’s Hubei province, where this virus began spreading among humans. It’s also a trend observed in Italy, another devastated region with several thousand deaths.
Now, given that all but a handful of states have implemented stay-at-home orders, the air-quality shifts are also being seen in the United States. This offers a rare — and unintended — large-scale experiment for scientists to see how human emissions contribute to hazardous air quality and analyze the effectiveness of particular policy ideas.
These maps show the amounts of nitrogen dioxide in the atmosphere, a key ingredient in smog, between March 1 and April 5, 2019, when compared to the same period this year. They show the subtle decreases in NO2 in much of the country, including the Mid-Atlantic, Northeast, Ohio Valley and Southwest.
According to Yifang Zhu, a professor at UCLA’s Fielding School of Public Health, the Los Angeles region, long notorious for its traffic and smog, has seen improvements in air quality in recent weeks that can be partly tied to the coronavirus response.
Before stay-at-home orders were issued March 16, Zhu said, the EPA’s Air Quality Index, which incorporates multiple air pollutants, including NO2 and PM2.5 (fine particulate matter), was about 60, or in the “moderate” category. Since then, it has improved by about 20 percent and recorded the longest stretch of “good” air quality in March seen since at least 1995.
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