During COVID-19 locks, the Internet was flooded with images from Delhi to Los Angeles, showing mountains usually hidden behind a smog or clear blue sky that was once gray.
People speculated that as fewer people traveled, industry slowed down and many airports closed functionally, pollution levels dropped everywhere.
They had, depending on your vantage point.
Researchers at the University of Washington in St. Louis have developed a method using satellite measurements that allowed them to determine nitrogen dioxide levels – NO2 – On a scale that has not been accessible so far – even in areas where there is no field monitoring capabilities. No2 It is a major contributor to smog associated with poor traffic or areas of intensive industry.
The method, developed in the laboratory of Randall Martin, the distinguished professor Raymond R. Tucker in the Department of Energy, Environment and Chemical Engineering, allows researchers to infer NO levels2 In small areas like a neighborhood.
When they used it to compare NO levels2 Before and during COVID-19-related locks worldwide, they found that although there was a significant decrease in NO2 Around the world in areas under closure, there were also significant gaps on a smaller scale.
The results were published January 19 in the journal nature.
“We can determine differences, not only from city to city, but within cities we have seen interesting differences in NO levels2“, Said Matt Cooper, the first author of the study.” The changes within the cities were not uniform; “In some areas, there has been a greater decline than in others.”
Prior to the COVID-19-related lock, Cooper worked on ways to improve NO detection2 In the atmosphere using new satellite technology. Then the plague struck.
“Interesting test case”
“It was an interesting test case for the new method,” Cooper said. “And there was a lot of interest in air quality, which seemed to have improved.”
Cooper has been able to improve methods that use modeling, satellites and ground-based monitoring data to deduce amounts of NO at the surface level2 At any point across the globe. This new method makes better use of satellite data at a finer resolution, allowing researchers to determine NO levels2 On a scale of about one kilometer.
Understanding NO levels2 It is important for a better understanding of human health. The chemical is one of the major air pollutants, and is a precursor to the formation of a fine particulate matter. High exposure to NO2 Related to a variety of health problems, most notably respiratory problems in nature, as well as a higher risk of mortality, in general.
Because it is formed primarily by burning fuel, researchers have suggested that COVID-related locking may lead to a decrease in NO2. They did. Significantly.
Given the changes expected by weather trends, and the fact that emissions have generally been declining in recent years due to technological improvements, the researchers were able to conclude a decrease in the NO level at the surface level2 Were almost 30% larger in countries with strict closures compared to those without.
Overall, Martin said, “the global decline during the lockout was similar to 15 years of annual reductions in emissions control.”
However, on closer inspection, the researchers found that the declines were not evenly distributed. “We see a very noticeable spatial variation,” Cooper said. “Find any city and you will see a signal.”
Take Atlanta, for example. Population Accounting, NO Concentration2 Decreased by 28% across the metro area between April 2019 and April 2020. But there is a lot of variance represented within this average rate.
For example, more than 1.2 million people in the region saw a decrease of more than 40% in NO2 Levels. However, nearly a million people experienced a decline of only 10% or less. The changes were generally greater for those living near coal or airport plants than in the heart of the city center.
Or Paris. More than a million people in the metropolitan area of ​​Paris have seen a decline in NO2 Of 75% or more, while other metro areas saw a decrease in NO2 Of 23% or less.
The benefits of this more subtle resolution go beyond identifying the unequal burden of pollution among neighbors. It can also help researchers better infer pollution levels in areas where there is no other way to determine NO levels.2. Much of the world does not have enough – or no – ground monitoring of pollutants.
Of the 215 cities the researchers surveyed, 68 had no previous land monitoring data. Most of these cities, the researchers noted, were in lower-income countries in Africa and Southeast Asia. The average gross national income per capita for these unsupervised cities was $ 7,000. This is compared to $ 25,000 for cities in countries with reliable land monitoring.
“Although lower-income countries are less likely to monitor local air quality,” Cooper said, “large changes prevent lock-in exposure to NO2 It happened regardless. “
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