Lockdown drove pollution changes between -- even within -- cities

Date:
January 19, 2022
Source:
Washington University in St. Louis
Summary:
A new modelling method allows researchers to measure levels
of nitrogen dioxide on a finer scale, revealing disparities in
exposure during COVID.



FULL STORY ========================================================================== During COVID-19 lockdowns, the internet was flooded with images from
Delhi to Los Angeles, showing mountains typically hidden behind smog or
clear blue skies where they were once gray.


========================================================================== People speculated that, because fewer people were driving, industry
slowed and many airports were functionally closed, levels of pollution
had dropped everywhere.

They had, depending on your vantage point.

Researchers from Washington University in St. Louis developed a method
using satellite measurements that allowed them to determine levels of
nitrogen dioxide -- NO2 -- on a scale never before accessible -- even
in areas where there are no monitoring capabilities on the ground. NO2
is a key contributor to the smog associated with bad traffic or areas
of intense industry.

Developed in the lab of Randall Martin, the Raymond R. Tucker
Distinguished Professor in the Department of Energy, Environmental &
Chemical Engineering, the method allows researchers to infer levels of
NO2 in regions as small as a neighborhood.

When they used it to compare levels of NO2 before and during
COVID-19-related lockdowns across the globe, they found that, although
there was a significant decrease in NO2 worldwide in areas under lockdown, there were also striking discrepancies on smaller scales.



==========================================================================
The results were published Jan. 19 in the journal Nature.

"We can determine differences, not just from city to city, but within
cities we were seeing interesting differences in levels of NO2," said
Matt Cooper, first author of the study. "Changes within cities weren't
uniform; some areas saw a larger decrease than others." Prior to the COVID-19-related lockdowns, Cooper had been working on ways to improve the detection of NO2 in the atmosphere using a new satellite technology. Then
the pandemic hit.

'Interesting test case' "It was an interesting test case for the new
method," Cooper said. "And there was plenty of interest in air quality,
which seemed to be improving." Cooper was able to improve on methods
that use modeling, satellites and ground- monitoring data to infer surface-level amounts of NO2 on any point on the globe. This new method
makes better use of the finer-resolution satellite data, enabling
researchers to determine levels of NO2 on a scale of about one kilometer.



========================================================================== Understanding levels of NO2 is important for a better understanding
of human health. The chemical is one of the primary air pollutants,
and it is a precursor to the creation of fine particulate matter. High
exposure to NO2 is associated with a variety of health problems, mainly respiratory in nature, as well as a higher risk of mortality, overall.

Because it is primarily formed by burning fuel, researchers suggested
the COVID-related lockdowns might lead to decreases in NO2. They did.

Significantly.

Taking into account the variations expected by weather trends, and the
fact that emissions have been generally decreasing over the past several
years due to technological improvements, the researchers were able to
infer decreases in surface-level NO2 were almost 30% larger in countries
with strict lockdowns versus those without.

Overall, Martin said, "The global decrease during lockdowns was comparable
to 15 years of annual reductions from emission controls." When they
took a closer look, however, researchers found that the decreases
were not evenly distributed. "We see very striking spatial variation,"
Cooper said. "Find any city and you'll see a signal." Take Atlanta,
for one. Accounting for population, the concentration of NO2 decreased
by 28% across the metro area between April 2019 and April 2020. But
there is a lot of variation represented within that average rate.

For example, more than 1.2 million people in the region saw a more than
40% decrease in NO2 levels. However, nearly 1 million people experienced decreases of only 10% or less. Changes were generally larger for those
living near coal- powered plants or the airport than in the downtown core.

Or Paris. More than 1 million people in the Paris metropolitan area saw
a decrease in NO2 of 75% or more, while other metro areas saw a decrease
in NO2 of 23% or less.

The benefits to this finer resolution go beyond identifying the unequal
burden of pollution between neighbors. It also can help researchers
better infer pollution levels in areas where there is no other way to
determine levels of NO2. A significant part of the world does not have sufficient -- or any - - ground monitoring of pollutants.

Of the 215 cities the researchers investigated, 68 had no previous
ground- monitoring data. Most of those cities, the researchers noted,
were in lower- income countries in Africa and Southeast Asia. The
average gross national income per capita for these unmonitored cities
was $7,000. That's in comparison with $25,000 for cities in countries
with reliable ground monitoring.

"Although lower-income countries are less likely to have local air
quality monitoring," Cooper said, "large lockdown-driven changes
in exposure to NO2 occurred regardless." special promotion
Explore the latest scientific research on sleep and dreams in
this free online course from New Scientist -- Sign_up_now_>>> academy.newscientist.com/courses/science-of-sleep-and-dreams ========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Brandie
Jefferson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Matthew J. Cooper, Randall V. Martin, Melanie S. Hammer,
Pieternel F.

Levelt, Pepijn Veefkind, Lok N. Lamsal, Nickolay A. Krotkov,
Jeffrey R.

Brook, Chris A. McLinden. Global fine-scale changes in ambient
NO2 during COVID-19 lockdowns. Nature, 2022; 601 (7893): 380 DOI:
10.1038/s41586- 021-04229-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220119121422.htm

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